Workshop on Surfaces, INterfaces and
Functionalization Processes in Organic
Compounds and Applications
IMEM – CNR Institute (Parma, Italy)
June 20th-22nd, 2012
Book of AbstractV
Cari amici e colleghi,
il Workshop SINFO nasce dalla volontà dei Direttori di alcuni Istituti del CNR, afferenti al
Dipartimento Materiali e Dispositivi, ora denominato Dipartimento Scienze Fisiche e Tecnologie
della Materia, di favorire il confronto a livello nazionale di ricercatori attivi nell’area dei composti
organici conduttivi, e dei dispositivi e delle interfacce ad essi correlate. L’iniziativa, che
auspichiamo possa non rimanere isolata in ambito dipartimentale, vuole essere innanzitutto una
“riunione di lavoro” e un vero e proprio “incontro culturale” a carattere interdisciplinare.
Essa deve essere inquadrata nell’interesse che la Fisica della Materia mostra oggi,
comunemente ad altre discipline scientifiche e tecnologiche, verso la ricerca di nuovi materiali e
funzionalità, in grado di favorire la maturazione di applicazioni tecnologiche innovative, nonché
costituire il punto di partenza per l’indagine di aspetti scientifici di base ancora inesplorati. In questi
termini, i composti organici, grazie alle loro ridotte proprietà di simmetria e alla molteplici
possibilità di funzionalizzazione, offrono un panorama vastissimo di potenzialità di sviluppo e
applicative che potranno essere pienamente sviluppate soprattutto in contesti di ricerca dove
competenze e tecniche provenienti da diversi settori scientifici siano messi a fattore comune.
Come “Programme Committe”, esprimiamo viva soddisfazione per l’ampia partecipazione
che SINFO ha saputo raccogliere presso varie istituzioni sia interne al CNR, con il coinvolgimento
di diversi Dipartimenti, sia legate al mondo Universitario. Va osservato che il criterio di
attribuzione delle presentazioni orali ha voluto garantire, oltre l’elevato valore scientifico dei
contributi proposti, anche un’adeguata rappresentanza di tutte le istituzioni intervenute. Ci sembra
doveroso anche sottolineare la qualità dei contributi poster che, nella quasi totalità dei casi, non è
inferiore a quelli selezionati per gli interventi orali.
Partendo dalla consapevolezza che per molti partecipanti, compreso gli organizzatori, questa
è la prima occasione di incontro e conoscenza, e che le tematiche proposte sono da considerarsi del
tutto innovative potremmo considerare SINFO come un opera di “teatro sperimentale”. In tal
senso, il successo dell’iniziativa non dovrà essere misurata dalla “prima rappresentazione”, dove la
curiosità della novità sa motivare più facilmente le persone, ma dalla partecipazione alla “seconda
serata” e dalle iniziative che i gruppi interessati saranno capaci di sviluppare grazie anche a questo
primo incontro di Parma. Non possiamo che augurarci che questa iniziativa di “teatro sperimentale”
possa evolvere in un “teatro stabile di innovazione”.
Buon lavoro,
Aldo Amore Bonapasta
Arrigo Calzolari
Antonio Cassinese
Luca Floreano
Tullio Toccoli
1
2
Surfaces, INterfaces and Functionalization Processes
in Organic Compounds and Applications (SINFO)
The workshop aims at providing scientists from the CNR - Department of Materials and Devices
with a forum to share the latest information and ideas on the fundamental properties of organic
semiconductor and small molecule overlayers as well as their future applications and
implementation into working devices.
It is expected to identify emerging routes for control and analysis of the electronic, magnetic, and
optical properties of organic compounds and systems, by joining the chemical and physical
investigation of fundamental properties with the new interdisciplinary routes of nanoscale device
design, synthesis of novel materials, and engineering of innovative functions in organic devices.
The workshop intends improving the communication among CNR research units, academia, and
research centers in order to develop a large coordination capability and to single out the research
directions to be implemented within the next European calls of FP7 and the forthcoming Horizon
2020 Program.
The technical sessions will focus mainly on:
Supported organic overlayers: Self-assembled monolayers, Oriented molecular growth, Molecular
anchoring, Organics on Transition Metal Oxides, Magnetic organic overlayers
Complex organic architectures: Organo-metallic hybrid junctions, Organic film templating,
Organic heterostructures, Charge transfer at hybrid interfaces
Applications of Organics for Electronics, Light Emission/Conversion and Sensing: Charge
transport and non equilibrium processes in hybrid architectures, Donor-acceptor molecular dyads,
Single molecule devices, Molecular recognition
Programme Committee
Aldo Amore Bonapasta (ISM)
Arrigo Calzolari (NANO)
Antonio Cassinese (SPIN)
Luca Floreano (IOM)
Tullio Toccoli (IMEM)
Steering Committee
Salvatore Iannotta (IMEM)
Alberto Morgante (IOM)
Dino Fiorani (ISM)
Lucia Sorba (NANO)
Ruggero Vaglio (SPIN)
3
Organizing Secretary
Rosella Magno (IMEM)
Isabella Rinaldi (IMEM)
Antonella Secondulfo (IMEM)
Paolo Marmiroli (IMEM)
Roberta De Donatis (SPIN)
Elisabetta Narducci (DMD)
4
PROGRAM
June 20th
Parma, June 20th-22nd 2012
Chairman Aldo Amore Bonapasta
13:00-14:30
Registration
14:30-15:00
Opening
15:00-15:40
Invited
Leonhard Grill
Fritz Haber
Institut Berlin,
Germany
Covalent linking of functional molecules on surfaces: Wires and networks
15:40-16:00
Talk
Giuseppe Maruccio
NANO
Molecule-nanoparticle hybrids for electronic and sensing applications
16:00-16:20
Talk
Paola Alippi
ISM
Molecule-surface coupling in ruthenium phthalocyanine dimers deposited on Ag(111):
a combined experimental and theoretical investigation
16:20-16:40
Talk
Gregor Kladnik
Ljubljana Univ.
Slovenia
Through-Space Charge Transfer in π-Coupled Molecular Systems Studied with
Resonant Photoemission and the Core-Hole Clock Method
16:40-17:10
Coffe break
17:10-17:30
Talk
Luca Beverina
UniMIB
Luminescent Heteroaromatics: efficient light guiding and concentration for electrical
power conversion
17:30-17:50
Talk
Carmine Antonio
Perroni
SPIN
Charge transport in single-crystal organic semiconductors
17:50-18:10
Talk
Vincenzo Palermo
ISOF
Graphene-organic composites for microelectronics and materials science
18:10-19:30
Poster
Chairman Antonio Cassinese
PROGRAM
June 21st
the morning
Parma, June 20th-22nd 2012
Chairman Arrigo Calzolari
9:00-9:40
Invited
Antonio Facchetti
Northwestern
Univ. USA
Organic Semiconductors and Interfaces Optimized for N-, P-, and Ambipolar
Transport
9:40-10:00
Talk
Valentina Tozzini
NANO
Reversible Hydrogen Storage by Controlled Buckling of Graphene Layers
10:00-10.20
Talk
Giorgio Contini
ISM
Long range ordered phenylene polymers by Ullmann’s reaction on Cu(110) from 1,4dibromobenzene precursors
10:20-10.40
Talk
Franco Bloisi
SPIN
Characterization of MAPLE (Matrix Assisted Pulsed Laser Evaporation)
deposited eumelanin thin films
10:40-11.10
Coffe break
11:10-11:30
Talk
Alessandro Mattoni
IOM
Atomistic investigation of self-assembled interlayers for efficient
photoconversion at polymer/metaloxide interfaces
11:30-11:50
Talk
Alice Ruini
NANO
Ab initio study of ZnO-based hybrid interfaces for photovoltaic application
11:50-12:10
Talk
Stefano Lettieri
SPIN
Probing electronic distribution at organic/oxide interface by optical second harmonic
generation: the case of PDI8-CN2 as “proper” n-type semiconductor
12:10-12:30
Talk
Valeria Lanzilotto
IOM
Charge transfer at the interface with the TiO2(110) surface: a comparative study
between perylene and PTCDI.
12:30-15:00
Lunch
6
PROGRAM
June 21st
the afternoon
Parma, June 20th-22nd 2012
Chairman Luca Floreano
15:00-15:40
Invited
Claudia Draxl
Humboldt Univ.
Berlin, Germany
Organic molecules inside carbon nanotubes:
From structural arrangements to their photo-physics
15:40-16:00
Talk
Emilia Annese
IOM
The role of the interface in the magnetic interaction between M-Phthalocyanine and
ferromagnetic film
16:00-16:20
Talk
Victor Erhokin
IMEM
Organic memristor as a thin film synapse-mimicking device
16:20-16:40
Talk
Mauro Sambi
UniPD
Fullerene/porphyrin supramolecular and covalent networks
on silver single crystal surfaces
16:40-17:10
Coffe break
17:10-17:30
Talk
Giancarlo Salviati
IMEM
Charge transfer in SiC/SiO2 core/shell NWs functionalized by SuMBD with fluorinated
porphyrins
17:30-17:50
Talk
Tobias Cramer
ISMN
Organic field effect transistors as transducers for neuronal network activity
17:50-18:10
Talk
Flavia Viola Di
Girolamo
SPIN
Ambipolar transport and charge transfer at the interface between Sexithiophene (T6)
and N,N’-bis (n-octyl)- dicyanoperylenediimide (PDI-8CN2) films
7
PROGRAM
June 22nd
Parma, June 20th-22nd 2012
Chairman Tullio Toccoli
9:00-9:40
Invited
Frank Schreiber
Tübingen Univ.
Germany
Organic-Organic Heterostructures
9:40-10:00
Talk
Antonio Valletta
IMM
Analysis of contact effects in high performance fully printed
p-channel Organic Thin Film Transistors
10:00-10.20
Talk
Yoshihiro Kubozono
Okayama, Japan
Interface control of phenacene field-effect transistors and excellent FET
characteristics
10:20-10.40
Talk
Michele Muccini
ISMN
Organic Light-Emitting Transistor technology based on Organic Heterostructures
10:40-11.10
Coffe break
11:10-11:30
Talk
Caterina Cocchi
NANO
Electronic and Optics of Short Graphene Ribbons: Field Enhancement and Edge
Functionalization
11:30-11:50
Talk
Letizia Savio
IMEM
Glutamic Acid at Ag surfaces: Self-Assembly in the Non-Zwitterionic Form
11:50-12:10
Talk
Aurora Rizzo
NANO
Organic Photovoltaic Devices with Colloidal TiO2 Nanorods as Key Functional
Components
12:10-12:30
Talk
Giovanni Di Santo
ELETTRA
Porphyrins and Metallo-Porphyrins on Ag(111): molecule-substrate adaptation and
interaction via induced chemical modication and metal inclusion
12:30-13:00
Closing
Remarks
8
Abstracts
(Oral)
9
Covalent linking of functional molecules on surfaces: Wires and networks
Leonhard Grill
Fritz-Haber-Institute of the Max-Planck-Society
Department of Physical Chemistry
Faradayweg 4-6
14195 Berlin, Germany
The construction of assemblies from individual functional molecules is not only of fundamental
interest for a better understanding of molecular interaction and reactivity, but also for potential
applications in novel materials, molecular machines and molecular electronics. Covalent bonding,
which provides high stability and the possibility of efficient charge transfer, is the desired
intermolecular interaction and it could be shown recently that this can be achieved on a surface [1].
In particular, the dehalogenation-based “on-surface-synthesis” process [2] turned out to be very
successful and was used by different research groups to create a variety of well defined molecular
nanostructures [3]. Its strength lies in its feasibility and the control over the final architectures,
because their shape and size is directly controlled via the composition of the initial molecular
building blocks as will be discussed in this talk. In addition to the growth on metal surfaces, also the
combination with inorganic crystallites is possible, thus creating an organic/inorganic hybrid system
[4]. In the next step, a novel strategy for the covalent connection in a hierarchical manner was
developed [5], thereby generating molecular species with a programmed reactivity. This is achieved
by using different halogen substituents, which allow the selective and sequential activation of
specific sites within each individual molecule. Such a hierarchical growth (Fig.1) is demonstrated
for homogeneous and heterogeneous structures with high selectivity.
Figure 1: Concept of hierarchical covalent growth by sequential activation of different sites within
each molecule (indicated in red and blue).
By using an anisotropic surface, the catalytically active sites of the surface can be identified in real
space [6] and substrate-directed growth and a preferred orientation of the molecular nanostructures
are achieved [5,6]. Finally, by pulling a polymer from a metallic surface, the conductance can be
measured for a single molecular wire as a continuous function of the electrode-electrode distance
[7].
References: [1] D. F. Perepichka et al., Science 323, 216 (2009), [2] L. Grill et al., Nature Nanotech. 2 687
(2007), [3] M. Lackinger et al., J. Phys. D : Appl. Phys. 44, 464011 (2011), [4] C. Bombis et al., Ang. Chem.
Int. Ed. 48, 9966 (2009), [5] L. Lafferentz et al., Nature Chem. 4, 215 (2012), [6] A. Saywell et al., Angew.
Chem. Int. Ed., DOI : 10.1002/anie.201200543 (2012), [7] L. Lafferentz et al., Science 323, 1193 (2009)
10
Molecule-nanoparticle hybrids for electronic and sensing applications
Shilpi Karmakar1, Elisabetta Primiceri1, Valentina Arima1, Ross Rinaldi1, Alessandro Paolo
Bramanti2 and Giuseppe Maruccio1
1
NNL Istituto Nanoscienze - CNR and Dipartimento di Matematica e Fisica "Ennio De Giorgi",
Scuola Superiore ISUFI, Università del Salento, Via per Arnesano, I-73100 Lecce, Italy.
2
STMicroelectronics Srl, Distretto Tecnologico, Via per Arnesano, I-73100, Lecce, Italy
Self assembled monolayers are at the basis of many modern prototype devices and sensors. More
recently, assembly of organic molecules on nanomaterials was targeted as a route toward increased
functionality in hybrid electronic devices or improved sensitivity in nanotech-based sensors. Here
applications of molecule-nanoparticle hybrids are described in both fields using an economical method
for the fabrication of large arrays of nanojunctions by only optical lithography and chemical etching [1].
First, we report on single electron tunnelling behaviour of nanogap electrodes bridged by bisferrocenegold nanoparticles hybrids (BFc-AuNP) [2]. A smart approach to probe molecular conduction is to use
metal nanoparticles (NPs) as a bridge between organic monolayers formed on metallic electrodes or to
bridge two nanoparticles with single molecules in order to achieve control on the interface [3-5].
Moreover, nanoparticles with functional organic shells are particularly interesting because single
electron tunneling in the NP can be exploited for reading the molecular information. In our work,
depending on the tunneling rates and regime, symmetric and asymmetric double barrier tunneling
junctions were obtained with the later exhibiting clear Coulomb staircase. No magnetoresistance effects
were observed as a result of an external magnetic field, pointing out that the BFc molecule remains
diamagnetic even after immobilization on NP.
As second proof of concept, we report on the fabrication of a nanobiosensor based on ssDNA-NP
hybrids and able to detect single hybridization events [6]. Specifically, targets are oligonucleotides
conjugated to gold nanoparticles and electrodes are functionalized with complementary ssDNA. As a
consequence of target-probe binding events, a conductive bridge forms between the two electrodes,
resulting in a quantized change in conductivity. This enables a robust detection of few (down to single)
hybridization events and can be potentially applied also to other binding events (like specific
interactions between proteins, antibodies, ligands and receptors). Moreover, target amplification
techniques (such as PCR) are no longer necessary.
[1] G. Maruccio et al., Small 3, 1184 (2007).
[2] S. Karmakar et al., Nanoscale 4, 2311 (2012).
[3] G. Maruccio, Nature Nanotechnology 7, 147 (2012).
[4] T. Dadosh et al., Nature 436, 677 (2005).
[5] Y.-S. Chen, M.-Y. Hong, and G. S. Huang, Nat Nano 7, 197 (2012).
[6] G. Maruccio et al., Analyst 134, 2458 (2009).
Corresponding author: Giuseppe Maruccio, NNL Istituto Nanoscienze - CNR and Dipartimento di Matematica e Fisica
"Ennio De Giorgi", Scuola Superiore ISUFI, Università del Salento, Via per Arnesano, I-73100 Lecce, Italy. e-mail:
[email protected]
11
Molecule-surface coupling in ruthenium phthalocyanine dimers deposited on
Ag(111): a combined experimental and theoretical investigation
Paola Alippi1, A.M. Paoletti1, G. Pennesi1, G. Rossi1, G. Mattioli1, F. Filippone1, A. Verdini2,
V.Lanzilotto2, A. Morgante2, and A. Amore Bonapasta1
1
CNR- Istituto di Struttura della Materia, via Salaria Km 29.3, I-00016 Monterotondo Stazione,
Rome(Italy)
2
CNR - Istituto Officina dei Materiali, Area Science Park – Basovizza, Ed.MM, Strada Statale 14
Km 163,5 I-34149 Trieste (Italy)
The ruthenium phthalocyanine molecule, (RuPc) 2 , presents a dimeric molecular structure, unique
among similar Pcs complexes and characterized by a Ru=Ru double bond connecting two parallel
Pc macrocycles. [1] Conduction properties are also different from those of other Pcs, since (RuPc) 2
is a good intrinsic semiconductor (σRT=1x10-5 Ω-1cm-1) even in absence of intentional doping, thus
suggesting the existence of distinctive Ru-ligand intramolecular interactions. In this work, we have
investigated the electronic properties of sub-monolayer, single-layer and multi-layers of (RuPc) 2 on
Ag(111) surface, with the aim of clarifying the peculiar properties of this molecule and their
modifications (if any) when it interacts with a metal substrate. The properties of the
(RuPc) 2 /Ag(111) systems have been extensively investigated by core level (XPS) and valence band
(UPS) photoelectron spectroscopy, near-edge X-ray absorption (NEXAFS) and resonant
photoemission (ResPES) measurements at the ALOISA beamline of the Elettra synchrotron
radiation facililty. On the side of the theory, the electronic structure of the isolated molecule has
been obtained by spin-polarized Density Functional Theory calculations with the hybrid HSE [2]
functional.
Combining experimental and theoretical results, a coherent picture of the (RuPc) 2 /Ag electronic
properties can be achieved, characterized by the existence of a doubly degenerate level located in
the (RuPc) 2 HOMO-LUMO gap, that is empty in the isolated molecule. This level, involving Ru-d
orbitals, is close to the Fermi level of the Ag substrate, as shown by a comparison of the calculated
densities of states of the isolated (RuPc) 2 with the UPS spectrum measured for the multilayer
(RuPc) 2 /Ag(111). It may play a key role in the (RuPc) 2 –substrate interaction by allowing surfaceto-molecule electron transfer: a remarkable shift (~1.5 eV) of Ru-3d 5/2 binding energy towards
lower values is indeed observed at submonolayer coverage with respect to the (RuPc) 2 multilayer
deposition. These results point out to strong molecule-surface coupling, possibly related also to the
a priori unexpected absence of ResPES signals at C-, N- and Ru-edges at any coverage.
[1] A. Capobianchi, A.M. Paoletti, G. Pennesi, G. Rossi, R. Caminiti, C. Ercolani, Inorganic
Chemistry, 33, 4635 (1994)
[2] J. Heyd, G. E. Scuseria, M. Ernzerhof, J. Chem. Phys. 124, 219906E (2006)
Corresponding author : Paola Alippi, CNR-ISM, via Salaria km 29,300 I-00015 Monterotondo
Stazione, Rome (Italy) ; Tel: (+39) 06 9067 2360 ; e-mail : [email protected]
12
Through-Space Charge Transfer in π-Coupled Molecular Systems Studied with
Resonant Photoemission and the Core-Hole Clock Method
Gregor Kladnik*1,2, Arunabh Batra3, Hector Vazquez3, Jeffrey S. Meisner4, Luca Floreano2, Colin
Nuckolls4, Dean Cvetko1,2, Latha Venkataraman3, Alberto Morgante2,5
1
Department of Physics, University of Ljubljana, Ljubljana, Slovenia
2
CNR-IOM Laboratorio Nazionale TASC, Basovizza SS-14, km 163.4, I-34012 Trieste, Italy
3
Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY
4
Department of Chemistry, Columbia University, New York, NY
5
Department of Physics, University of Trieste, Trieste, Italy
Understanding the role of inter-molecular interaction on through-space charge transfer
characteristics in π-stacked molecular systems is central to the rational design of electronic
materials. However, a quantitative study of charge transfer in such systems is often difficult due to
rather poor control over molecular morphology. Here, we use the core-hole clock implementation of
resonant photoemission spectroscopy to study the femtosecond charge-transfer dynamics in
cyclophanes, which consist of two precisely stacked π-systems held together by aliphatic chains.
We study two systems, [2,2]paracyclophane (22PCP) and [4,4]paracyclophane (44PCP), with
interring separations of 3.0 A and 4.0 A respectively. We find that charge transfer across the πcoupled system of 44PCP is about 20 times slower than in 22PCP. We attribute this difference to
the decreased inter-ring electronic coupling in 44PCP due to the larger inter-ring distance. These
measurements illustrate the use of core-hole clock spectroscopy as a general tool for quantifying
through-space coupling in π-stacked systems. All measurements were performed at the ALOISA
beamline at the Elettra synchrotron in Trieste, Italy.
Charge transfer from the top ring to the substrate is fast for 22PCP (left) but
slow for 44PCP (right) due to stronger localization of the LUMO in 44PCP.
* Corresponding author: Gregor Kladnik, Department of Physics, University of Ljubljana, Jadranska 19,
1000 Ljubljana, Slovenia, email: [email protected]
13
Luminescent Heteroaromatics: efficient light guiding and concentration for
electrical power conversion
A. Sanguineti, M. Sassi, G. Vaccaro, A. Monguzzi, F. Meinardi, R. Tubino, Giorgio A. Pagani and
L. Beverina*
University of Milano-Bicocca, Department of Materials Science, 53 Via Cozzi, Milano, 20125, Italy
[email protected]
The potential of solar power is enormous, yet still largely unexploited because of the high cost of
efficient silicon-based solar cells. Moreover, the efficiency of standard photovoltaic devices
strongly depends on the light incidence angle and intensity.
Luminescent Solar Concentrators (LSCs) could provide cost
reduction, while ensuring operational capabilities under diffuse
illumination conditions.1 LSCs are slabs of transparent, high optical
quality materials doped with luminescent molecules. The molecules
absorb sunlight and emit inside the slab. Since the refractive index of
the slab is higher than that of air, most of emitted light is guided to
edges and there collected by small area solar cells. However, device
dimensions are usually limited by re-absorption of the emitted light.2
Highly efficient plastic based single layer LSCs, requires the design of
luminophores having complete spectral separation between absorption
and emission spectra (large Stokes-shift).
We show how the careful combination of π-excessive and π-deficient
heteroaromatics in highly conjugated Figure 1. LSCs under
structures enables the preparation of UV irradiation
highly
efficient
fluorophores
possessing almost no re-absorption. We will also show how it is
possible to prepare LSCs prototypes by bulk polymerization of a
fluorofore solution in acrylate monomers directly in a mold
possessing the required thickness. Alongside with such completely
organic LSCs, we will shows how it is possible to exploit the
unique emitting properties of lanthanides for the synthesis of
colorless chelates exibiting strong visible or NIR emission upon
UV excitation.
Such lanthanide chelates enable the preparation of colorless LSCs,
Figure 2. LSCs under capable to replace the window panels of large buildings without
diffuse ambient illumination
colour distortion.
References.
(1)
(2)
(3)
Hernandez-Noyola, H.; Potterveld, D.; Holt, R.; Darling, S. B. Energy Environ. Sci. 2012, 5,
5798–5802.
Fattori, V.; Melucci, M.; Ferrante, L.; Zambianchi, M.; Manet, I.; Oberhauser, W.;
Giambastiani, G.; Frediani, M.; Giachi, G.; Camaioni, N. Energy Environ. Sci. 2011, 4,
2849–2853.
Sanguineti, A.; Monguzzi, A.; Vaccaro, G.; Meinardi, F.; Ronchi, E.; Moret, M.; Cosentino,
U.; Moro, G.; Simonutti, R.; Mauri, M.; Tubino, R.; Beverina, L. Chem. Phys. Phys. Chem.
2012, Advance Article DOI: 10.1039/C2CP40791D
14
Charge transport in single-crystal organic semiconductors
C.A. Perroni, A. Nocera*, V. Marigliano Ramaglia, and V. Cataudella
Università “Federico II” Napol and CNR-SPIN
*Università Roma Tre
Spectral, optical, and transport properties of organic semiconductors are analyzed in single-crystalbased field-effect transistors. Different approaches have been used for models with electron
coupling to low frequency inter-molecular modes [1,2]: the self-consistent Born approximation
valid for weak electron-phonon coupling, the coherent potential approximation exact for infinite
dimensions, and numerical diagonalization for finite lattices. With increasing temperature, the width
of the spectral functions gets larger and larger, making the approximation of a quasiparticle less
accurate. On the contrary, their peak positions are never strongly renormalized in comparison with
the bare ones. As expected, the density of states is characterized by an exponential tail
corresponding to localized states at low temperature. For weak electron-lattice coupling, the optical
conductivity follows a Drude behavior, while for intermediate electron-lattice coupling, a
temperature-dependent peak is present at low frequency. For high temperatures and low particle
densities, the mobility always exhibits a power-law behavior as a function of temperature. With
decreasing particle density, at low temperature, the mobility shows a transition from metallic to
insulating behavior. Results are discussed in connection with available experimental data in
oligoacenes.
In particular, the effects of dimensionality [3] and the interplay between low frequency
intermolecular and high-frequency intra-molecular modes [4] have been investigated. Finally, the
interplay between electron-phonon coupling and disorder strength have been analyzed in organic
semiconductors grown on polarizable gates [5].
[1] V. Cataudella, G. De Filippis and C.A. Perroni, Phys. Rev. B 83, 165203 (2011).
[2] C.A. Perroni, A. Nocera, V. Marigliano Ramaglia, and V. Cataudella, Phys. Rev. B 83, 245107
(2011).
[3] F. Gargiulo, C.A. Perroni, V. Marigliano Ramaglia, and V. Cataudella, Phys. Rev. B 84, 245204
(2011).
[4] C.A. Perroni, V. Marigliano Ramaglia, and V. Cataudella, Phys. Rev. B 84, 014303 (2011).
[5] C.A. Perroni and V. Cataudella, arXiv:1109.6342.
Corresponding author: C.A. Perroni, Dipartimento Scienze Fisiche, Via Cinthia I-80126 Napoli, [email protected] , tel.
+39081676855
15
Graphene-organic composites
for microelectronics and materials science
Emanuele Treossi,1 Andrea Liscio, 2 Manuela Melucci, 3 Andrea Schlierf, 2 Zhen-Yuan Xia,2
Vincenzo Palermo2
Laboratorio MISTE-R , Via Gobetti 101, Bologna
CNR-ISOF, Bologna, Italy.
CNR-ICCOM, Sesto Fiorentino, Italy.
[email protected]
The term “graphene” refers to a single layer of carbon atoms, arranged in a honeycomb, highly
conjugated lattice. The sheets have a thickness of few angstroms, and can have a lateral size of
hundreds of microns. Until few years ago it was thought that single layer graphene could not be
isolated given that, at any finite temperature, thermal fluctuations would have destroyed the 2D
structure.
This common belief was shattered in 2004, when a group of researchers from Manchester
demonstrated that it was not only possible but even relatively easy to obtain single sheets of
graphene by repeated exfoliation of graphite with scotch tape.
The outstanding optical, electronic and structural properties of graphene have attracted a huge
amount of research activity. In more recent times, the research expanded to the study of even more
complex, composites materials, in which graphene is blended with organic materials to obtain new
properties or improve the existing ones.
We will describe some recent results obtained at ISOF on the production and study of grapheneorganic composites, and in particular on:
 Covalent functionalization of graphene sheets with optically active oligothiophenes.
 Charge transport in graphene-polythiophene transistors.
 Local current mapping and patterning of reduced graphene oxide.
References
1.
Journal of the American Chemical Society, (2011) 133, 14320.
2.
Journal of Materials Chemistry, (2011) 21, 2924.
3.
Journal of Materials Chemistry, (2010) 20, 9052.
4.
Journal of the American Chemical Society, (2010) 132, 14130.
5.
Journal of the American Chemical Society, (2009) 131, 15576.
16
Organic Semiconductors and Interfaces Optimized for N-, P-, and
Ambipolar Transport
Antonio Facchetti*
Polyera Corporation 8045 Lamon Avenue, Skokie, IL 60077and
2
Northwestern University, 2145 Sheriran Road, Evanston IL 60208 (USA)
1
1. N-type
2. Ambipolar
3. P-type
Current Density / mA/cm2
Organic thin-film transistors (OTFTs) are candidates for several new display and electronic circuit
applications.1 However, to enable OTFT-based technologies, certain issues must be addressed
starting with: 1. Enhance organic semiconductor performance, especially for n-channel. 2. Enable
solution-processability with environmentally-acceptable solvents. 3. Demonstrate bias and thermal
stress stable devices. 4. Furthermore, it would be desirable to enable robust top-gate architectures
with reproducible performance. In this paper we report for the first time on the TFT performance of
organic n-channel semiconductors exhibiting very large carrier mobilities (2-3 cm2/Vs for injketprinted TFTs, >10 cm2/Vs for single crystals), exceptional bias tress and thermal stress stability.
Furthermore, we demonstrate for the first time that top-gate TFT performance on glass can be
controlled by the chemistry of the glass substrate. Finally, we report recent results on materials for
ambipolar transport and solar cells.
15
OPV10:C70PCBM, AM1.5G 100mW/cm2
10
5
0
-5
-10
-15
-0.8 -0.4 0.0
0.4
0.8
Voltage / V
Figure 1. Building blocks used to synthesized several semiconducting materials for TFTs and OPVs.
References
1. A. Facchetti Chem Mater., 23, 733 (2011).
2. (a) H. Yan, Z. Chen, Y. Zheng, C. E. Newman, J. Quinn, F. Dolz, M. Kastler, A. Facchetti
Nature 457, 679 (2009). b) H. Yan, Y. Zheng, R. Blache, C. Newman, S.F. Lu, J. Woerle, A.
Facchetti Adv. Mater., 20, 3393 (2008).
3. D. Boudinet, M. Benwadih, S. Altazin, J.-M. Verilhac, E. De Vito, C. Serbutoviez, G. Horowitz,
A. Facchetti J. Am. Chem. Soc. 133, 9968 (2011).
[email protected]
Corresponding author: afacchetti@polyera. com [email protected]
17
Reversible Hydrogen Storage by Controlled Buckling of Graphene Layers
V. Tozzini, S. Goler, T. Mashoff, V. Pellegrini, C. Coletti, F. Beltram, and S. Heun
Graphene is an intriguing material that shows promises for hydrogen storage. We shall present in
this talk theoretical and experimental evidence that by changing in a controlled fashion the
curvature of graphene, the energy barrier for adsorbing and desorbing atomic hydrogen attached to
the pi-bonds of graphene can be removed thereby making it possible to attach and release hydrogen
at room temperature, a mechanism that can be exploited for room temperature hydrogen storage
applications.
By means of calculations based on density-functional theory, we demonstrate a tunability of the
binding energies of more than 2 eV by changing the sheet out-of-plane deformation up to +-0.2Å,
with the convex regions allocating the energetically favored hydrogen binding sites. We simulate
the process of hydrogen chemisorption on corrugated graphene and release under the application of
time-dependent mechanical deformations. Our results show that the corrugation of the graphene
sheet and the controlled inversion of its curvature yield fast and efficient storage and release of
hydrogen [1]. Our corrugated graphene device can potentially reach gravimetric capacities up to
8%wt and reversibly store and release hydrogen by external control of the local curvature at
ambient conditions and with fast kinetics.
Initial experimental tests of the capacity of corrugated graphene to bind hydrogen are carried out on
epitaxial graphene grown on SiC(0001). The initial carbon layer (also known as the interface,
zerolayer or buffer layer) below the monolayer graphene has been theoretically predicted to have a
high curvature with an amplitude of 1.2Å over a length of ~2nm making it an optimal laboratory for
testing the interaction between hydrogen and graphene as a function of curvature [2]. To this end
we shall discuss scanning tunneling microscopy experiments of hydrogenated graphene sheets
grown on the silicon face of silicon carbide. In these experiments we were able to atomically
resolve, for the first time, the hexagonal lattice of the zerolayer verifying that it is topologically
identical to monolayer graphene [3]. Upon obtaining atomic resolution, we hydrogenated the
sample in situ and studied the position of hydrogen atoms on the graphene lattice as a function of
curvature [4]. We found that atomic hydrogen binds to the carbon atoms in the convexly curved
areas, in agreement with our theoretical evaluations based on DFT calculations [1], which indicates
an increase of ~0.15eV in binding energy with respect to flat graphene (0.7eV). We finally
measured the carbon hydrogen bond height to be ~1Å, in agreement with the expected bond length
of 1.1Å [1].
[1] V. Tozzini and V. Pellegrini. J. Phys. Chem. C115, 25523 (2011).
[2] F. Varchon et al. Phys. Rev. B 77, 235412 (2008).
[3] S. Goler et al. submitted; arXiv:1111.4918
[4] S. Goler et al. in preparation.
Corresponding author: Valentina Tozzini. CNR- Istituto NANO - e-mail: [email protected]
18
Long range ordered phenylene polymers by Ullmann’s reaction on Cu(110)
from 1,4-dibromobenzene precursors
G. Contini, M. Di Giovannantonio, M. El Garah*, J. A. Lipton-Duffin*, F. Rosei*
Istituto di Struttura della Materia, CNR, Via Fosso del Cavaliere 100, 00133 Rome, Italy
*INRS-EMT, Université du Québec, 1650 Boulevard Lionel-Boulet, Varennes, QC J3X 1S2,
Canada
Confined surface polymerization reaction in ultra-high vacuum (UHV) conditions has recently
gained much attention. Ullmann reaction [1], one of the oldest known ways to couple aromatic
units, is a mechanism that has been introduced to link two organic molecules through C-C bond
using catalytic surface and build one- and two-dimensional covalent organic network [2, 3].
Here we present the successful formation of a complete monolayer of ordered poly(para-phenylene)
(PPP) polymers on Cu(110) using 1,4-dibromobenzene as precursor molecules by Ullmann’s
reaction; polymers result to be aligned along a crystal direction of copper substrate. A copper
surface completely covered by polymers is obtained using bromine-based precursors.
The polymer formation was investigated, as a function of the substrate temperature, using scanning
tunneling microscope (STM), low energy electron diffraction (LEED) and X-ray photoelectron
spectroscopy (XPS). The 1,4-dibromobenzene monomer dosed at room temperature on Cu(110),
dissociate into phenyl biradicals and assemble into the so-called ‘‘protopolymer’’ chains at the
surface, which are not linked by covalent C–C bonds. The conjugated PPP polymer was formed
eating the Cu(110) surface to 200°C.
This catalytic method opens the possibility of producing individual conjugated aromatic polymers
with complex structure and tailored functionality. The method can be extended to the synthesis of
more complex architectures (including 2D polymers), to be used, for example, in nanoelectronic
circuits.
[1] Ullmann F., Bielecki J., Ber. Deutsch. Chem. Ges. 1901, 34, 2174.
[2] Lipton-Duffin J. A., Ivasenko O., Perepichka D. F., Rosei F., Small, 2009, 5, 592.
[3] Bieri M., Nguyen M.-T., Groning O., Cai J., Treier M., Aït-Mansour K., Ruffeux P., Pignedoli
C. A., Passerone D., Kastler M., Moullen K., Fasel R., J. Am. Chem. Soc. 2010, 132, 16669.
Corresponding author: Giorgio Contini, Istituto di Struttura della Materia, CNR, Via Fosso del Cavaliere 100, 00133
Rome, Italy. [email protected]
19
Characterization of MAPLE (Matrix Assisted Pulsed Laser Evaporation)
deposited eumelanin thin films
F. Bloisia,b, A. Pezzellac, M. Barrab, M. Alfèd, F. Chiarellab, A. Cassinesea,b, L. Vicaria,b
a
: CNR-SPIN
b
: Physics Science Department / University of Naples “Federico II”
c
: Department of Organic Chemistry and Biochemistry
d
: CNR-IRC Istituto di Ricerche sulla Combustione
Melanins1 (mainly eumelanin, and pheomelanin) constitute an important class of (brown-black or
red-brown, respectively) organic pigments almost ubiquitous in animals, plants, and
microorganisms.
Eumelanins originate, in vivo, by oxidative polymerization of the indolic monomer precursor 5, 6dihydroxyindole-(DHI) and the 5, 6-dihydroxyindole-2-carboxylic acid (DHICA). Syntetic
eumelanin is obtained, mimicking this procedure, by in vitro oxidation of DHI and DHICA2.
Eumelanins (either natural or synthetic) are organized in characteristic supramolecular structures3
and are characterized by a featureless optical absorption with a monotonic decrease across the
whole visible light spectrum from short (400 nm, UV) to long (800 nm, IR) wavelengths. Due to
this feature, eumelanins behave as very efficient photoreceptors4 and show other interesting
physical properties such as the charge transport capabilities both under light5 and in darkness6,7,
with a high dependence on the hydration state8.
Eumelanin poor solubility in common solvents represents a severe limitation for preparing thin
films. We experimentally demonstrate9,10 that eumelanin films can be successfully deposited taking
advantage from the peculiar characteristics of the MAPLE (Matrix Assisted Pulsed Laser
Evaporation) thin film deposition technique, using as target a frozen water suspension ablated by IR
(1064nm) laser radiation from a Q-switched Nd:YAG pulsed laser source. The low laser absorption
of ice together with the high absorption of eumelanin suggests that the target ablation is due to laser
energy absorbed by the eumelanin molecules, followed by thermal energy transfer, and ejection of
ice/water/vapor containing undamaged eumelanin molecules and supramolecular structures.
Structural characterization (UV-VIS, FTIR, AP-MALDI) confirms that the deposited films maintain
the characteristics of the eumelanin biopolymer. Morphological characterization (AFM) shows that
the film surface features are highly depending on the deposition parameters and slightly on the
substrate temperature during MAPLE deposition and is almost uninfluenced by post-annealing.
Preliminary electrical characterization shows that eumelanin films seem to obey Ohm’s law without
evidence that charge injection from gold electrodes is affected by the presence of significant energy
barriers. Moreover, charge transport is drastically reduced in vacuum, even if the phenomenon is at
least partially reversible.
1 G.Prota: Melanins and Melanogenesis (Academic Press, San Diego, 1992). ISBN:9780125659703
2 A.Napolitano, A.Pezzella, M.d’Ischia, G.Prota: Tetrahedron 52:8775-8780 (1996)
3 A.A.R.Watt, J.P.Bothma, P.Meredith: Soft Matter 5:3754-3760 (2009)
4 P.Meredith, B.J.Powell, J.Riesz, S.P.Nighswander-Rempel, M.R.Pederson, E.G.Moore: Soft Matter 2:37-44 (2006)
5 M.Abbas, F.D’Amico, L.Morresi, N.Pinto, M.Ficcadenti, R.Natali, L.Ottaviano, M.Passacantando, M.Cuccioloni,
M.Angeletti, R.Gunnella: Eur. Phys. J. E 28:285-291 (2009)
6 J.McGinness, P.Corry, P.Proctor: Science 183:853-855 (1974)
7 M.M.Jastrzebska, S.Jussila, H.Isotalo: J. Mater. Sci. 33:4023-4028 (1998)
8 M.M.Jastrzebska, H.Isotalo, J.Paloheimo, H.Stubb: J. Biomater. Sci. Polym. Ed. 7:577-586 (1996)
9 F.Bloisi, A.Pezzella, M.Barra, F.Chiarella, A.Cassinese, L.Vicari: J. Appl. Phys. 110:026105 (2011)
10 F.Bloisi, A.Pezzella, M.Barra, M.Alfè, F.Chiarella, A.Cassinese, L.Vicari:Appl. Phys. A 105:619-627 (2011)
Corresponding author: Francesco Bloisi e-mail: [email protected]
Dip. Scienze Fisiche / Fac. Ingegneria, Piazzale V. Tecchio, 80 - 80125 Napoli (Italy)
20
Atomistic investigation of self-assembled interlayers for efficient
photoconversion at polymer/metaloxide interfaces
C. Melis (1,2), G. Malloci (2), C. Caddeo(1,2), M.I. Saba(1,2), L. Colombo (1,2), A. Mattoni (2)*
(1)Department of Physics, University of Cagliari I-09042 Monserrato (Cagliari)
(2)Istituto Officina dei Materiali del Consiglio Nazionale delle Ricerche (CNR-IOM), Unita' SLACS
Cagliari I-09042 Monserrato (Cagliari), Italy
Polymer metaloxide hybrids have emerged as promising systems for future solid-state
photovoltaics. The actual microstructure of the polymer/metaloxide interface critically controls the
photoconversion efficiency that is still too low[1]. Here we adopt molecular dynamics to generate
models of polymer/metaloxide interfaces (e.g. P3HT/ZnO[1,2]) and we study the effect of
molecules that can self-organize at the interface. We consider both the cases of optically active
metal-organic macrocyclic complexes (e.g. zinc phthalocyanines ZnPc’s[3]) and small organic
heterocyclic compounds. As for the first case, we provide evidence that ZnPc’s lie parallel to the
ZnO surface and self-assemble into elongated stripes[3] that are able to red-shift the optical
absorption and are beneficial for charge injection. As for the second case, we consider ordered
interlayers formed by heterocyclic molecules covalently bonded to the metaloxide. By suitable
choices of the molecules, the corresponding interlayer is able to improve the polymer organization
at the interface, and eventually the photoconversion efficiency[4]. This work is funded by the Italian
Institute of Technology (IIT) Seed Project “POLYPHEMO” and Regione Autonoma della
Sardegna under L.R. 2007.
References
[1] M. I. Saba, et al. J. Phys. Chem. C 115, 9651–9655 (2011)
[2] C Caddeo, et al. J. Phys. Chem. C, 115, 16833-16837 (2011)
[3] C. Melis et al. ACS Nano 5 9639 (2011)
[4] E. Canesi et al., submitted for publication
Corresponding author:
Alessandro Mattoni, CNR-IOM SLACS Cagliari
c/o Dipartimento di Fisica, Cittadella Universitaria 09042 Monserrato (CA)
tel. +39 070 6754868 fax: +39 070 6754892
email: [email protected], web: www.dsf.unica.it/~mattoni
21
AB INITIO STUDY OF ZnO-BASED HYBRID INTERFACES FOR
PHOTOVOLTAIC APPLICATIONS
Arrigo Calzolari1, Alice Ruini1,2,*, Alessandra Catellani3
CNR-NANO Istituto Nanoscienze, Centro S3, Modena Italy
2
Dipartimento di Fisica, Università di Modena e Reggio Emilia, Modena Italy
3
CNR-IMEM Parco Area della Scienza, Parma Italy
1
Metal-oxide nanoparticles may be sensitized to harvest visible radiation in working solar cells, upon
proper functionalization. However, the principles regulating interactions between the oxide layer
and the rest of the photovoltaic cell are poorly understood. Indeed, upon sensitization with organic
layers, the semiconductor surface faces a wide range of possible scenarios, driving the formation of
interfaces with specific spatial arrangements and novel electronic properties, affecting both light
harvesting and the generation of the photovoltaic current.
In order to provide hints for the design of efficient interfaces and control the different contributions
at an atomistic level, we characterize the optoelectronic and transport properties of the main
subsystems that form the active layer of a prototypical ZnO-based solar cell, by means of ab initio
DFT calculations.
We report on the functionalization of the non-polar ZnO(10-10) surface upon the adsorption of
prototypical chromophore linkers [1], such as catechol cyanin dyes [2], by also considering the
presence of water solvent [3]. The resulting type-II staggered interface is recovered in agreement
with experiments: its origin is traced back to the presence of molecular-related states in the gap of
the metal-oxide electronic structure and its tunability is demonstrated as a function of molecule
dipole moment and aromaticity. We extend this analysis [4] also to other hexagonal semiconductor
substrates (e.g. SiC, GaN, InN, CdS, CdSe), appealing for optoelectronic applications. The
comparison with different substrates allows us to draw relevant conclusions in a unified frame, also
in terms of surface states and superficial stress.
References
[1] A. Calzolari, A. Ruini, A. Catellani, J. Am Chem. Soc. 133, 5893 (2011).
[2] A. Calzolari, et al, J. Phys. Chem. A 113, 8801 (2009).
[3] A. Calzolari, et al, J. Chem. Phys. 132, 114304 (2010).
[4] A. Calzolari, A. Ruini, A. Catellani, preprint (2012).
Corresponding author:
Alice Ruini
Dip di Fisica, Univ. di Modena e Reggio E. and CNR-NANO, Centro S3
Via Campi 213/A,
I-41125 Modena
22
Probing electronic distribution at organic/oxide interface by optical second
harmonic generation: the case of PDI8-CN2 as “proper” n-type semiconductor
S. Lettieri1,2*, F. Ciccullo2, L. Mazzei2, A. Cassinese1,2, P. Maddalena1,2
1
2
CNR-SPIN, I-80126 Napoli (Italy)
Dipartimento di Scienze Fisiche, Università di Napoli “Federico II”, I-80126 Napoli (Italy)
Knowledge of electronic properties at semiconductor interfaces is of fundamental interest for a
number of applications, such as in organic FETs (OFETs), ruled by formation of conductive
channel between the source-drain electrodes. Specific studies on charge layers at organic/oxide
interfaces are often based on electrical characterization analysis (both ex-situ [2] of in situ [3]),
while approaches based on laser spectroscopy seem to represent an interesting novelty in the field.
Among the various optical spectroscopy techniques utilized to probe surfaces and interfaces, second
harmonic generation (SHG) have gained wide recognition for its ability to determine the electronic
structure and dynamics of surfaces. It offers significant advantages over conventional surface
spectroscopies for study of buried interfaces (e.g. elimination of material damage associated with
charged particle beams, absence of charging effects, probing of solid/solid interfaces thanks to the
large optical penetration depth). Furthermore, being SHG an electronic phenomenon, it allows to
probe all interfacial charge and not the mobile charge only, as well allowing to probe built-in
electric fields associated to charge accumulation/depletion at interfaces [4] even in absence of
charge transport.
Here we discuss about how polarization-resolved SHG analysis allows to probe electronic
redistribution and charge accumulation at organic/oxide interface where OFET channel is formed.
In particular, an ad-hoc developed model based on superposition of 2D and 3D effective
polarization P2ω (originating from organic surface and organic/SiO2 interface, respectively) is used
to describe recently obtained results for PDI8-CN2 films as well as α-6T/ PDI8-CN2 double layers
deposited on Si/SiO2 substrates. The obtained behavior of effective susceptibility as function of film
thickness suggests a way to probe the charge accumulation layer and local built-in field at
heterojunction without recurring to in-situ electrical characterization.
The results suggest the presence of accumulation layer extending up to 6-7 molecular layers in
PDI8-CN2 even in absence of gate field, thus strengthening the picture in which such materials acts
as a “proper” n-type semiconductor. Finally, we will point out why SHG analysis, as sensitive to
net charge, is expected to be less influenced by spatial correlation than charge transport analysis:
this underlines novel possibilities offered by combination of SHG and in-situ electrical analysis.
[1] A. Dodalabapur, L. Torsi, and H. E. Katz, Science 268, 270 (1995)
[2] F. Dinelli, M. Murgia, P. Levy, M. Cavallini, F. Biscarini, D.M. De Leeuw, Phys. Rev. Lett. 92, 116802 (2004)
[3] A. Shehu, S.D. Quiroga, P. D’Angelo, C. Albonetti, F. Borgatti, M. Murgia, A. Scorzoni, P. Stoliar, F. Biscarini,
Phys. Rev. Lett. 104, 246602 (2010)
[4] O.A. Aktsipetrov, A.A. Fedyanin, E.D. Mishina, A.N. Rubtsov, C.W. Van Hasselt, M.A.C. Devillers, T. Rasing,
Phys. Rev. B 54 (1996) 1825.
*
Corresponding author. E-mail: [email protected]
23
Charge transfer at the interface with the TiO2(110) surface:
a comparative study between perylene and PTCDI.
Valeria Lanzilotto1,2, Gregor Bavdek1,3, and Luca Floreano1
CNR-IOM, Laboratorio TASC, Basovizza SS14, Km. 163.5, 34149 Trieste, Italy
2
Department of Physics, University of Trieste, via Valerio 2, 34100 Trieste, Italy
3
Faculty of Education, University of Ljubljana, Ljubljana, Slovenia
1
Thanks to its strong structural anisotropy, the TiO2(110) surface has become the most diffuse
playground among dielectrics to attempt the oriented growth of optically active organic layers
[1][2]. This substrate is made even more attractive since the surface can become conductive upon
charge injection, that is associated with the emergence of a new defect state in the band gap. We
have recently shown that the excess of charge is transferred to a few specific subsurface Ti sites
irrespective of the nature of the charge source (either by surface reduction [3] or alkaly metal
deposition [4]). Perylene and its derivatives are known to be used in organic photovoltaic cells
thanks to their capability to donate or accept electrons.
By coupling the TiO 2 (110) surface with this kind of molecules we have tried to control the excess
of charge present on the surface. In particular, we have performed a comparative study on the
interaction of perylene (donor) and PTCDI (acceptor) with the defect state of TiO 2 . The molecules
have shown a common self‐assembly mechanism driven by the good match between the molecular
structure and the substrate lattice parameters. However we have found that only PTCDI effectively
interacts with the defect state of TiO 2 , as observed by Synchrotron radiation spectroscopy.
The films growth was followed by He diffraction and RHEED. A polarization dependent NEXAFS
study allowed us to determine the molecular orientation and the eventual modification of the
LUMOs structure. The chemical discrimination among the electronic states in the valence band was
obtained through resonant photoemission.
[1] V. Lanzilotto, C. Sanchez‐Sanchez, G. Bavdek, D. Cvetko, M. F. Lopez, J.A. Martin‐Gago and
L. Floreano “Planar growth of pentacene on the dielectric TiO 2 (110) surface” J. Phys. Chem. C 115
(2011) 4664.
[2] C. Sanchez‐Sanchez, V. Lanzilotto, C. Gonzalez, A. Verdini, P. de Andres, L. Floreano, M.F.
Lopez, and J.A. Martin‐Gago, “Floating molecular layer of Spinning C60 molecules on TiO 2 (110)
surfaces” Chem. Eur. J. in press.
[3] P. Krueger, S. Bourgeois, B. Domenichini, H. Magnan, D. Chandesris, P. Le Fevre, A.M. Flank,
J. Jupille, L. Floreano, A. Cossaro, A. Verdini and A. Morgante “Defect states at the TiO 2 (110)
surface probed by resonant photoelectron diffraction” Phys. Rev. Lett. 100 (2008) 055501.
[4] P. Krueger, J. Jupille, S. Bourgeois, B. Domenichini, A. Verdini, L. Floreano, A. Morgante
“Intrinsic nature of the excess electron distribution at the TiO 2 (110) surface” Phys. Rev. Lett. 108
(2012) 126803.
24
Organic molecules inside carbon nanotubes:
From structural arrangements to their photo-physics
Claudia Draxl
Humboldt-Universität zu Berlin, Newtonstraße 15, D-12489 Berlin
Nano-hybrid materials consisting of single-wall carbon nanotubes (SWNT) with endohedrally
bound organic molecules combine the unique mechanical and electronic properties of nanotubes
with the optical characteristics of π-conjugated molecules. Hence they are considered as promising
candidates for nano-devices in opto-electronic applications. Only recently it could be shown [1] that
such peapods can be synthesized, and indeed emit light in the visible range of the spectrum.
Here we investigate in more detail structural, electronic and optical properties of oligo-thiophenes
as well as polymers embedded in zig-zag nano-tubes with various diameters. We find the systems to
be exclusively bound through van der Waals forces [2]. This observation is confirmed by the
electronic structure as it appears as a mere superposition of the bands coming from the two
components. Nevertheless, the electronic states are not purely aligned with respect to the vacuum
level, but corrections arising from the tube curvature and corresponding charge rearrangements
have to be taken into account. Our analysis allows for a prediction of the level alignment, which in
turn could be used for the design of such materials yielding particular optical properties. In the
latter, excitonic effects govern the low-energy emission in the isolated molecules. These are
substantially altered by the interaction of the pea and the pod in the excited state as revealed by
solving the Bethe-Salpeter equation in the framework of many-body perturbation theory. This, in
turn, can explain reduced exciton lifetimes as measured by time-resolved photo-luminescense [3].
[1]
[2]
[3]
M. A. Loi, J. Gao, F. Cordella, P. Blondeau, E. Menna, B. Bártová, C. Hébert, S. Lazard, G.
A. Bottone, M. Milko, and C. Ambrosch-Draxl, Adv. Mater. 22, 1635 (2010).
Matus Milko and Claudia Ambrosch-Draxl, Phys. Rev. B 84, 085437 (2011).
Jia Gao, Pascal Blondeau, Patrizio Salice, Enzo Menna, Barbora Bártová, Cécile Hébert,
Jens Leschner, Matus Milko, Claudia Ambrosch-Draxl, and Maria Antonietta Loi,
Small 7, 1721 (2011).
25
The role of the interface in the magnetic interaction between M-Phthalocyanine
and ferromagnetic film
Emilia Annese1,2, Francesco Casolari2, Jun Fujii1, Ivana Vobornik1,G. Panaccione1, Giorgio
Rossi1,3
1
IOM CNR, Laboratorio TASC, Area Science Park- Basovizza, 34149 Trieste
Università di Modena e Reggio Emilia, via Campi 213/A, 41100 Modena
3
Dipartimento di fisica, Università di Milano, Via Celoria 16, 20133 Milano
2
The control of organic nanostructures suitable for nano-electronics, spintronics and sensor
applications can be achieved by tuning their electronic, optical, catalytic and magnetic properties at
organic/inorganic interfaces. The feasibility of incorporating organic materials into spintronics
devices requires the comprehension of the electronic and magnetic interaction at
organic/ferromagnetic interface [3-5]. Several open aspects still need to be explored at the
organic/ferromagnetic interfaces: i) the type of magnetic coupling; ii) the role of the organic
molecules and iii) the role of substrate surface magnetism.
With this respect, the choice of the molecules and the substrates are primary parameters. Metalphthalocyanines (C32H16N8-M, MPc) are large planar molecules showing a high level of
flexibility that makes them ideal building blocks for functionalized organic systems [1]. Fe and Co
films, epitaxially grown on Cu substrate, show magnetic anisotropy from perpendicular to in plane
directly related to the film thickness [2].
In this work, we have investigated the behaviour of MPc films deposited on ferromagnetic Fe (Co)
film by X-ray absorption Spectroscopy and X-ray Magnetic Circular Dichroism. We have observed
and monitored the magnetic coupling between 3d atoms within MPc and the substrate at room and
low (80 K) temperatures. We have analyzed the evolution of the magnetic coupling as a function of
MPc thickness. We have found that only MPc molecules at the interface are mainly involved in the
coupling with Co film.
[1] S.R. Forrest, Nature 428, 911 (2004)
[2] J.Shen et al, Phys. Rev. B. 56, 11134 (1997)
[3]A. L. Rizzini et al, Phys. Rev. Lett. 107, 177205 (2011)
[4]H. Wende et al, Nat. Mat., 6, 516 (2007)
[5]A. Scheybal et al, Chem. Phys. Lett. 411, 214 (2005)
Corresponding author: Emilia Annese, [email protected]
26
Organic memristor as a thin film synapse-mimicking device
Victor Erokhin1 and Tatiana Berzina1
1
CNR-IMEM, Parco Area delle Scienze 37/A - 43124 Parma, 43100 Italy
Main task of the present work was the realization of the element that can be a key node of
networks allowing Hebbian or synaptic learning [1]. In terms of electrical connections, this element
must increase its conductivity as a function of its involvement into the process of signal transfer.
The element has been realized [2] basing on the property of polyaniline (PANI) to be highly
conducting in the oxidized state and insulating in the reduced one. The active zone of the element is
composed by the heterojunction of PANI with solid electrolyte (lithium salt doped polyethylene
oxide (PEO)). Silver wire is attached to the PEO and is used as a reference electrode. This reference
electrode is connected to one of the terminal electrodes. Thus, considering its attachment to the
external circuit, the present element can be considered as a memristive device or memristor [3],
while its function is very similar to the memistor [4], where the electronic conductivity is a function
of the transferred ionic charge. Cyclic voltage-current characteristics of the device for electronic (a)
and ionic (b) currents are shown in Fig. 1. More details on the construction and properties of the
organic memristive device can be found in [5].
The system has revealed the possibility of the generation of current auto-oscillations when the
charge-accumulation element is in the system.
Finally, a part of the nervous system of the pond snail Lymnaea stagnalis, responsible for the
learning during feeding, has been realized basing on 2 memristive devices.
The obtained results can form a basis of the new computational paradigms, where the same
elements will perform storage and processing of the information allowing learning and decision
making.
a
b
Fig. 1. Cyclic dependences of the electronic (a) and ionic (b) current of the organic
memristor upon the applied voltage. Empty rhombs correspond to the voltage
increase, while filled squares correspond to the voltage decrease.
References
1
D.O. Hebb, The origin of behavior. A Neurophsychological theory, New York: Wiley and
Sons, 1961.
2
V. Erokhin, T. Berzina, M.P. Fontana, J. Appl. Phys., 97, 2005, 064501 .
3
L. Chua, IEEE Trans. Circuit Theory, 18, 1971, 507-519.
4
B. Widrow, W.H. Pierce, J.B. Angell, Office of Naval Research, Technical Report, 15522/1851-1, 1961.
5
V. Erokhin, M.P. Fontana, J. Computational Theor. Nanosci., 8, 313-330 (2011).
Corresponding author:
Tel. (0521) 90 52 35; e-mail:
27
[email protected]
Fullerene/porphyrin supramolecular and covalent networks
on silver single crystal surfaces
F. Sedona, M. Di Marino, T. Carofiglio, E. Lubian, M. Casarin and M. Sambi
Dipartimento di Scienze Chimiche, Università di Padova and Consorzio INSTM;
Via Marzolo 1, 35131 Padova, Italy.
A large number of 2D nano-networks has been obtained in recent years on different single crystal
substrates by deposition of organic molecules whose self‑assembly is driven by subtle equilibria
between non-covalent intermolecular and vertical (molecule-substrate) weak and reversible
interactions. Such non-covalent interactions ultimately lead to long-range ordered surface
nanostructures, which are however intrinsically fragile and do not resist to aggressive conditions
such as high temperature thermal annealing or air exposure, have little mechanical stability and do
not provide efficient intermolecular charge transport. Covalent bonding between the molecular
building units (MBU) can overcome these limitations, but –as recently remarked1 – the issue in this
case becomes the low degree of long-range order which is usually attained, mainly due to the low
activation temperature for covalent bonds formation between the MBU that leads to the rapid
growth of larger polimolecular fragments with low mobility, in turn hindering the attainment of an
ordered structure.
In this contribution we first show that multi-component supramolecular self-assemblies of
exceptional long-range order and low defectivity are obtained if C60 and either pristine or variously
aminated tetraphenylphenylporphyrins (i. e. TPP, TPP-NH2, TPP-(NH2)2 and TPP-(NH2)4) are
assembled on Ag low-index surfaces by sequential evaporation of the MBU on the substrate surface
in the sub-monolayer range, followed by annealing2. Subsequently, we introduce a two step bottomup approach to construct 2D long range ordered, covalently bonded fullerene/porphyrin binary
nanostructures3. In the first place, reversible supramolecular interactions between C60 and either
TPP-(NH2)2 or TPP-(NH2)4 are exploited to obtain very large domains of an ordered binary
network; subsequently an addition reaction between fullerene molecules and the amino-groups on
porphyrin units, triggered by thermal treatments, is used to freeze the supramolecular nanostructure
with covalent bonds. In this approach, the preorganization step produces a supramolecular network
wherein the MBU are linked to each other in a such a way that the subsequent covalent bondformation implies minimal rearrangements in the superstructure, since substantial repositioning
inevitably leads to a high level of disorder. These results show promising potential for the synthesis
of highly ordered networks of surface-supported functional copolymers.
1. Perepichka, D. F.; Rosei, F. Science 2009, 323, 216.
2. Di Marino, M.; Sedona, F.; Sambi, M.; Carofiglio, T.; Lubian, E.; Casarin, M.; Tondello E.
Langmuir 2010, 26, 2466.
3. Sedona, F.; Di Marino, M.; Sambi, M.; Carofiglio, T. ; Lubian, E.; Casarin, M.; Tondello, E.
ACS Nano 2010, 4, 5147.
Corresponding author: Mauro Sambi, phone: +390498275189; e-mail: [email protected]
28
Charge transfer in SiC/SiO 2 core/shell NWs functionalized by SuMBD with
fluorinated porphyrins
Giancarlo Salviati1, Filippo Fabbri1, Francesca Rossi1, Lucia Nasi1, Giovanni Attolini1, Salvatore
Iannotta1, Lucrezia Aversa2, Roberto Verucchi2, Marco Nardi2, Flavio Mariani3, Tiziano Rimoldi3,
Luigi Cristofolini3
1
IMEM-CNR Institute, Parco Area delle Scienze 37/A, 43124 Parma (Italy)
2
IMEM-CNR Institute, Via alla Cascata 56/C – Povo, 38123 Trento (Italy)
3
Physics Department, University of Parma, 43124 Parma (Italy)
Novel functionalizations of nanostructured materials have attracted the attention for the possible
application in the field of sensing and biomedical applications. SiO 2 /SiC coaxial nanowires (NWs)
are of interest because of the unique physical and chemical properties of 3C-SiC, in particular its
biocompatibility, and the presence of a SiO 2 native shell that favours surface functionalization.
Here, we report on preliminary results of the functionalization of 3C-SiC NWs with partiallyfluorinated tetraphenylporphyrins (H2TPP(F)). The morphological, structural and optical properties
of the nanostructures are analyzed by means of Field Emission Scanning Electron Microscopy,
Atomic Force Microscopy (AFM), High Resolution Transmission Electron Microscopy,
Fluorescence and Cathodoluminescence (CL) Spectroscopy and imaging and X-ray Photoelectron
Spectroscopy (XPS), before and after the functionalization..
The surface functionalization is performed by means of Supersonic Molecular Beam Deposition in
order to kinetically activate bonding formation between the molecules and the nanostructure
surface. The kinetic energy of the molecules, deposited by helium carrier gas, is evaluated to be
around fifteen eV, a value about three orders of magnitude higher than the thermal evaporation
kinetic energy of a conventional MBE. The functionalization of the NWs has been demonstrated by
comparing XPS analyses of molecules deposited on SiO 2 /Si layer and on SiC/SiO 2 core/shell NWs.
The chemical shifts of the carbon 1s and of the fluorine lines shapes at the surface interface with
respect to the corresponding molecular bulk material have been evidenced as the proof of the
functionalization. On the other hand the optical response of the molecules at the surface shows a
noticeable effect due to the interaction which is another strong indication of molecule-surface stable
bonding. The fluorescence monitored as a function of the kinetics of the growth is in fact strongly
depending on the kinetic energy of the molecular precursors of the beam. In particular the first
monolayer shows specific features in the emission spectrum, not present in the bulk porphyrin,
when the kinetic energy of the molecules is around 25 eV, which are tentatively ascribed to a lower
symmetry, surface-bound porphyrin specie.
The optical investigation carried out by CL spectroscopy and imaging, reveals that the
functionalized NWs have three order of magnitude higher integrated intensity in comparison with
the molecules deposited on bulk substrates. This effect is related to an efficient energy transfer
between the NWs and the molecules. Analytical electron microscopy elemental mapping confirms
an homogeneous 20 nm thick H2TPP(F) shell around each single NW. This value coincides with
the maximum thickness achieved by the molecules layer on bulk substrates, as shown by AFM
studies. Those findings are encouraging in the prospective to employ this functionalized system for
different nano-medical applications.
29
ORGANIC FIELD EFFECT TRANSISTORS AS TRANSDUCERS FOR
NEURONAL NETWORK ACTIVITY
T. Cramer1(a), B. Chelli(a), M. Murgia(a), F. Biscarini(a)
(a)
ISMN-CNR Bologna, Via Gobetti 101, 40129 Bologna, Italy
In neurology and neuroscience there is a need for new approaches to interface neuronal cellular
activity with electronics transducers. Organic field effect transistors offer tailored surface
properties, flexibility and high sensitivity to electronic potential changes at the liquid interface.
These properties make them interesting candidate for extracellular recordings and stimulation of
neuronal network activity.
In the talk we present pentacene bottom contact ultra thin film transistors operated by a liquid gate
as a new test bed for transduction and stimulation of neuronal network activity. The devices are
highly sensitive to small changes of the electrochemical potential of the solution and show
sufficient stability towards the harsh conditions needed for cell culturing. We show that neural stem
cells can be differentiated into neuronal networks on top of functional devices without any
additional layer of cell adhesive molecules (figure 1B).[1] In order to investigate the coupling
between the neuronal network and the transistor we analyze the noise in current transients after
electrical stimulation. By comparison to reference devices we prove that the transient patterns can
be attributed to the activity of the neuronal network (figure 1C). Our results are in agreement with a
capacitive coupling between cell induced ionic currents and carrier currents in the semiconductor as
established for CMOS transistors (figure 1A).[2]
Figure 1. (A) Model for the electronic coupling between cellular membrane potential and transistor channel; (B)
fluorescent micrograph of differentiated neurons on top of a transistor with interdigitated electrodes; (C) Averaged
change in the cells cleft potential as a function of stimulation potential.
[1] I. Tonazzini, E. Bystrenova, B. Chelli, P. Greco, P. Stoliar, A. Calo, A.Lazar, F. Borgatti, P.
D'Angelo, C. Martini, F. Biscarini, Biophys. J. 98, 2804 (2010).
[2] P. Fromherz, Eur. Biophys. J. 28, 254-258 (1999).
1
[email protected]
30
Ambipolar transport and charge transfer at the interface between Sexithiophene
(T6) and N,N’-bis (n-octyl)- dicyanoperylenediimide (PDI-8CN2) films
F.V. Di Girolamo*, M.Barra, F. Chiarella, S.Lettieri, M.Salluzzo, A. Cassinese
CNR-SPIN and Department of Physics Science, University of Naples Federico II, Piazzale Tecchio
80125, Naples, Italy
(*e-mail address : [email protected] ; phone: +390817682548)
DRAIN-SOURCE CURRENT [A]
Since the beginning, the research in the field of organic semiconductors has been focused on the
investigation of materials and devices with improved optical and electrical properties. Considerable
efforts have been recently devoted to the synthesis of n-type semiconductors able to effectively
transport the charge even in ambient conditions. Among these, perylene diimides core
functionalized with electron withdrawing cyano groups (CN2) display very high performances in
terms of charge carrier mobility and air-stability. This achievement has consequently opened the
way to the fabrication of a large variety of devices requiring the combination of both p- and n-type
semiconductors. In particular, Organic Heterostructure Field Effect Transistors. Heterostructures
obtained by combining 'p-type' and 'n-type' organic semiconductors are attracting considerable
attention for the interesting physical phenomena arising at organic/organic interfaces, as well as for
their potential application in ambipolar field-effect transistors [1] [2]. Here we report on the
observation of an interfacial charge transfer effect in high quality Sexithiophene (T6)/ N,N’-bis (n
octyl)-dicyanoperylenediimide (PDI-8CN2) heterostructures, fabricated in-situ by a controlled
sequential evaporation of T6 and PDI-8CN2 thin films on Si/SiO2 substrates [3]. The electrical
characterization of several heterostructures as a function of the thickness of each film shows that the
hole and electron transport cannot be explained by invoking only the properties of the individual
layers. Electrical characterization and non-linear optical spectroscopy give clear indications of
charge transfer between T6 and PDI-8CN2 layers, accompanied by band offset and interfacial
charge accumulation (heterojunction effect) at the organic/organic interface. Signatures of such
effect were the enhancement of drain-source current at zero gate voltage, a shift of gate threshold
voltage in transfer-curves and an enhanced second harmonic generation related to a built-in
interfacial electric field. Gate voltage-tunable negative transconductance has been also observed in
heterostructures composed by thin T6 layers and explained in terms of gate voltage tunable
recombination phenomena occurring in the hole/electron accumulation layer.
3x10
-5
2x10
-5
2x10
-5
1x10
-5
1x10
-6
5x10
0
-5
4x10
F
-5
-5
6x10
E
-40
0
40
A
D
-5
2x10
b)
C
G
B
0
-40
0
40
GATE VOLTAGE [V]
Fig.1. (a) The double-layered configuration device; (b) Measured for heterostructure devices (configuration A) with different T6 thicknesses (T6 1 nm
open brown circles, A, T6 2nm open orange diamonds, B, T6 4.5 nm green circles, C, T6 7.5 nm open black triangles, D, T6 15 nm filled violet
triangles, E) compared with the ones of unipolar transistors based on PDI-8CN2 (filled blue squares) and T6 (filled red circles ) single layers. In the
inset of (b), the transfer-curves of three of the devices realized in the configuration A, evidencing the NTC effect..
[1] T.Jung, B. Yoo, L. Wang, A.Dodabalapur, B. A. Jones, A. Facchetti, M. R. Wasielewski, and T. J. Marks Appl.Phys.Lett 88, 183102 (2006).
[2] F. Zhu, K. Lou, L. Huang, J. Yang, J. Zhang, H. Wang, Y. Geng, and D. Yan Appl. Phys. Lett. 95, 203106 (2009).
[3] F. V. Di Girolamo, M. Barra, F. Chiarella, S. Lettieri, M. Salluzzo and A. Cassinese, Ambipolar transport and charge transfer at the interface
between Sexithiophene (T6) and N,N’-bis (n-octyl)- dicyanoperylenediimide (PDI-8CN2) films, accepted in Phys. Rev. B.
31
Organic-Organic Heterostructures
Frank Schreiber
Institut für Angewandte Physik, Universität Tübingen, 72076 Tübingen, Germany
[email protected]
http://www.soft-matter.uni-tuebingen.de/
Functional organic materials and devices are becoming increasingly complex. Their preparation and
growth is, not surprisingly, similarly complex, and the resulting structure will be determined by a
competition between kinetics and thermodynamics, which is not trivial to predict in particular for
multi-component systems. We discuss general concepts [1] and recent examples [2,3] of organicsbased heterostructure growth in the context of kinetic effects compared to thermodynamic
(equilibrium) structure. We also discuss the associated optical properties and the question of
coupling between donor and acceptor components [4,5]. Finally, we comment on the implications
for the optical and electronic properties as well as possible device applications with focus on
organic photovoltaics [6]. Contributions by a number of collaborators, including A. Hinderhofer, C.
Frank, K. Broch, J. Novak, R. Banerjee, A. Gerlach, and S. Kowarik, are gratefully acknowledged.
Schematic of structure formation of A:B mixtures (left) and a possible coupling scheme (right) [1].
[1] A. Hinderhofer and F. Schreiber. Organic-organic heterostructures: Concepts and applications,
Chem. Phys. Chem. 13 (2012) 628
[2] A. Hinderhofer et al., Templating effect for organic heterostructure film growth: Perfluoropentacene on
diindenoperylene, J. Phys. Chem. C 115 (2011) 16155
[3] A. Hinderhofer et al., Structure and morphology of co-evaporated pentacene-perfluoropentacene thin films, J. Chem.
Phys. 134 (2011) 104702
[4] K. Broch et al., Optical evidence for intermolecular coupling in mixed films of pentacene and perfluoropentacene,
Phys. Rev. B 83 (2011) 245307
[5] F. Anger et al., Photoluminescence spectroscopy of pure pentacene, perfluoropentacene and mixed thin films, J.
Chem. Phys. 136 (2012) 054701
[8] J. Wagner et al., High fill factor and open circuit voltage in organic photovoltaic cells with diindenoperylene as
donor material, Adv. Funct. Mater. 20 (2010) 4295
32
Analysis of contact effects in high performance fully printed
p-channel Organic Thin Film Transistors
A. Valletta, M. Rapisarda, A. Daami*, S. Jacob*, M. Benwadih*, R. Coppard*,
G. Fortunato and L. Mariucci
CNR – IMM, via del fosso del Cavaliere 100, Roma, Italy
*CEA/Liten/DTNM/LCEI, 17 rue des Martyrs, Grenoble, 38054 cedex 9, France
Contact effects have been analyzed in fully printed p-channel OTFTs based on a pentacene
derivative as organic semiconductor and with Au source/drain contacts. In these devices, contact
effects lead to an apparent decrease of the field effect mobility with decreasing L and to a failure of
the gradual channel approximation (GCA) in reproducing the output characteristics. In particular,
the GCA is able to reproduce almost quantitatively the output characteristics only in the case of the
long channel OTFTs. As the channel length is reduced below 100 µm, GCA progressively fails in
the reproduction of the experimental data at high Vds, severely overestimating the saturation current
and allowing to reproduce only the output conductance at Vds as low as 2 – 3 V.
We have taken the contact effects into account by introducing an OTFT model in which the
metal-organic semiconductor interface is schematized as a parasitic element that induces a voltage
drop (Vc) mainly at the source contact. The potential Vc can be calculated by solving a modified
GCA equation
Vgs −Vc
W
Id =
G (V )dV
L Vgs ∫−Vds
where G(V) is the channel conductance calculated from the transfer characteristics, measured at
very low Vds, of a long channel OTFT, for which the influence of the contact is negligible. The
calculated Id-Vc curves, show the typical behavior of the electrical characteristics of a diode in the
reverse operation regime, with an appropriate reverse current and ideality factor.
Hence, the experimental data have been reproduced by two-dimensional numerical simulations
that included a Schottky barrier (Φb = 0.46 eV) at both source and drain contacts and the effects of
field-induced barrier lowering. The barrier lowering was found to be controlled by the Schottky
effect for an electric field E < 105 V/cm, while for higher electric fields we found a stronger barrier
lowering presumably due to other field-enhanced mechanisms. The analysis of numerical
simulation results showed that three different operating regimes of the device can be identified:
1) low |Vds|, where the channel and the Schottky diodes at both source and drain behave as gate
voltage dependent resistors and the partition between channel resistance and contact resistance
depends upon the gate bias;
2) intermediate Vds, where the device characteristics are dominated by the reverse biased diode at
the source contact;
3) high |Vds|, where pinch-off of the channel occurs at the drain end and the transistor takes
control of the current. We show that these three regimes are a general feature of the device
characteristics when Schottky source/drain contacts are present, and therefore the same analysis
could be extended to TFTs with different semiconductor active layers.
Corresponding author: Antonio Valletta ( e-mail: [email protected] )
33
Interface control of phenacene field-effect transistors and excellent FET
characteristics
Y. Kubozono, X. He, N. Kawai, N. Komura, S. Hamao, R. Eguchi, H. Goto, T. Kambea
Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan
a) Department of Physics, Okayama University, Okayama 700-8530, Japan
We fabricated field-effect transistors (FETs) with thin films and single crystals of phenacene
molecules, picene, [6]phenacene and [7]phenacene. These FETs showed p-channel FET
characteristics and clear O2 sensing properties. The highest field-effect mobility, , in these thin
film FETs was 3.5 cm2 V-1 s-1 after storing the FETs in O2. The high  values and O2 sensing
properties found in these FETs may lead to the future application toward practical electronics.
Contrary to high values in phenacene thin film FETs, the value was still lower by two orders of
magnitude in picene single crystal FET.
Recently, we fabricated the picene single crystal FETs with hydrophobic parylene-coated high-k
gate dielectrics, which showed the low-voltage operation (threshold voltage of 30 V) and higher 
value (0.45 cm2 V-1 s-1) than that (~10-2 cm2 V-1 s-1) in the picene single crystal FETs fabricated
previously. Furthermore, we inserted electron-acceptor molecule, tetracyanoquinodimethane
(TCNQ), between source/drain electrodes and picene single crystals, which reduced clearly contact
resistance in the FET transports. The highest  value reached 1.3 cm2 V-1 s-1 in picene single crystal
FET, which was higher by two orders of magnitude than the  value in the previous one. Thus, the
interface control between gate dielectrics and picene single crystals or between source/drain
electrodes and picene single crystals improved the FET characteristics of picene single crystal FET.
We further investigated temperature dependence and anisotropy of FET characteristics in picene
single crystal FET. The transfer integral of picene single crystals is large along b-axis and the
anisotropy in the single crystal FET directly reflects the transfer integrals between picene molecules.
We measured transport characteristics of picene single crystal FET by use of four-terminal
measurement to remove the affect of contact resistance. The band transport properties shown in
temperature dependence of  in picene single crystal FET are discussed based on the relation
between carrier densities estimated from Hall effect and capacitance.
We also fabricated [6]phenacene and [7]phenacene single crystal FETs and measured their FET
characteristics in a wide temperature region. The anisotropy of transport properties is also
investigated as in picene single crystal FET. In this presentation, I will show the FET characteristics
of phenacene thin film and single crystal FETs. The improvement of the FET characteristics
realized through the interface control is discussed based on their energy diagram and interface
dipole induced at interface. The high-density carrier-accumulation into the phenacene thin films and
single crystals realized by use of electric double layer (EDL) capacitor will also be reported. The
high-density carrier-accumulation is of significance for electrostatic control (tuning) of physical
properties in solid phenacenes. Finally, I will talk on superconductivity of metal-doped phenacene
solids.
Corresponding author: Yoshihiro Kubozono ([email protected])
34
Organic Light-Emitting Transistor technology
based on Organic Heterostructures
RAFFAELLA CAPELLI1, STEFANO TOFFANIN1, ROBERTO ZAMBONI2, ANTONIO
FACCHETTI3, AND MICHELE MUCCINI1,4
1
Consiglio Nazionale delle Ricerche (CNR), Istituto per lo Studio dei Materiali Nanostrutturati
(ISMN), via P. Gobetti 101, I-40129 Bologna, Italy
2
Consiglio Nazionale delle Ricerche (CNR), Istituto per la Sintesi Organica e la Fotoreattività
(ISOF), via Gobetti, 101, 40129, Bologna, Italy
3
Polyera Corporation,
SKOKIE, IL 60077 -5318
USA
4
E.T.C. s.r.l., via P. Gobetti 101, 40129 Bologna
The organic light-emitting transistor (OLET) is an emerging optoelectronic device having the
structure of a thin-film transistor and the capability of light generation [1]. Bright/multicolor OLETs
may allow electroluminescent display fabrication with simpler driving circuits. Furthermore, the
most advanced OLETs encompass a huge technological potential for the realization of intense
nanoscale light sources for a variety of applications, including miniaturized disposable photonic
bio-sensing devices and highly integrated optoelectronic systems.
In terms of performance and reliability, OLED technology is by far the most developed and active
matrix OLED displays have been introduced into the market. However, detrimental device-related
processes affecting OLED operation under high injection conditions are the exciton-charge
interactions and the photon losses at the electrodes. At the base of the OLET development there is
the possibility to enable new display/light source technologies, and exploit a transport geometry to
suppress deleterious photon losses and exciton quenching mechanisms inherent in the OLED
architecture. Here, recent advances and future prospects of light-emitting field-effect transistors
will be discussed, with particular emphasis on organic semiconductors and the role played by the
material properties, device features and the active layer structure in determining the device
performances. In particular, we introduce the concept of using a p-channel/emitter/n-channel
trilayer semiconducting heterostructure in OLETs, providing a new approach to markedly improve
OLET performance. In this architecture, exciton–charge annihilation and electrode photon losses
are prevented. Our devices are >100 times more efficient than the equivalent OLED, >2X more
efficient than the optimized OLED with the same emitting layer and >10 times more efficient than
any other reported OLETs.
[1] M. Muccini, A bright future for organic field-effect transistors. Nature Mater. 5, (2006) 605-613.
[2] R. Capelli, S. Toffanin, G. Generali, H. Husta, A. Facchetti and M. Muccini, Organic light-emitting
transistors with an efficiency that out-performs the equivalent light-emitting diodes. Nature Mater. 9 (2010)
496-503.
35
Electronic and Optics of Short Graphene Ribbons: Field Enhancement and
Edge Functionalization
Caterina Cocchi, Deborah Prezzi, Alice Ruini, Marilia J. Caldas* and Elisa Molinari
S3 Center, CNR - Nanoscience Institute, Modena, IT
Physics Department, University of Modena and Reggio Emilia, IT
*Institute of Physics, University of San Paulo, BR
The fabrication of nanoscale graphene ribbons of finite length is now reaching atomic scale
accuracy and extreme edge control [1]. Here we present a theoretical investigation of the optical
excitations of elongated nano-flakes and short ribbons, carried out by means of quantum chemistry
semi-empirical methods [2]. We focus both on intrinsic field enhancement effects and on
modifications of the optical properties induced by edge covalent functionalization.
We find that the optical spectra of H-passivated short graphene ribbons are dominated at low energy
by excitations with strong intensity, comprised of characteristic coherent combinations of a few
single-particle transitions with comparable weight. They give rise to stationary collective
oscillations of the photoexcited carrier density extending throughout the flake, and to a strong field
enhancement. These effects are robust and tunable with respect to width and length variations and
can be exploited to design nanoantennas and other nanoplasmonic applications [3].
We show that edge covalent functionalization is an efficient strategy to modulate the electronic and
optical properties of graphene nano-flakes and ribbons. By tuning electron affinity and ionization
potential, all-graphene optoelectronic applications can be designed [4], including type-II (staggered)
nano-junctions which allow for photoinduced charge separation [5]. We finally discuss the effects
of functionalization-induced distortions on the optical properties of these graphene nanostructures
[6].
References:
[1] J. Cai et al,. Nature 466, 470–473 (2010); S. Blankenburg et al., ACS Nano 6, 2020-2025
(2012);
[2] AM1 model: M. Dewar et al,. J. Am. Chem. Soc. 107, 3902–3909 (1985); ZINDO model: J.
Ridley and M. Zerner, Theor. Chem. Acta 32, 111–134 (1973);
[3] C. Cocchi et al. J. Phys. Chem. Lett. 3, 924-929 (2012);
[4] C. Cocchi et al,. J. Phys. Chem. C 115, 2969-2973 (2011);
[5] C. Cocchi et al. J. Phys. Chem. Lett. 2, 1315–1319 (2011);
[6] C. Cocchi et al. submitted (2012)
Corresponding author:
Caterina Cocchi, S3 Center – CNR Nano, Modena, IT - [email protected]
36
Glutamic Acid at Ag surfaces: Self-Assembly in the Non-Zwitterionic Form
L. Savio1*, M. Smerieri12, L. Vattuone12, M. Rocca12 I. Tranca3, D. Costa4, F. Tielens3
1
2
3
IMEM-CNR, Via Dodecaneso 33, 16146 Genova, Italy
Dipartimento di Fisica, Via Dodecaneso 33, 16146 Genova, Italy
UPMC Univ Paris 06, UMR 7197, and CNRS, UMR 7609, Laboratoire de Réactivité de Surface,
8 rue Galilée, F-94200 Ivry-Sur-Seine, France
4
Laboratoire de Physico-Chimie des Surfaces, ENSCP, ParisTech,
11 rue P. et M. Curie, F-75005 Paris, France
The understanding of the interactions between biomolecules and inorganic surfaces is mandatory
for all those applications in which this interaction wants to be either exploited (biomaterials,
nanoelectronics, hybrid material design) or avoided (fouling, hygiene). The complexity of bioinorganic interfaces, however, caused their characterisation at the molecular level to be still in its
infancy. Amino acids are protagonists of this kind of fundamental studies, since they are the basic
constituents of peptides and proteins and are small enough to be assumed as a prototype for the
adsorption of bio-molecules at surfaces. In most cases they adsorb in the zwitterionic form, while
anionic adsorption was sometimes detected.
We have recently investigated the interaction of (S)-Glutamic Acid (Glu) with LMI Ag surfaces in
the temperature range 250 K<T<400 K by experimental and theoretical methods. Our study shows
that Glu molecules adsorb always in the non-zwittterionic form [1,2,3], at variance with the
majority of cases reported in literature. Moreover, they self-assemble in different geometries
depending on the substrate and on the deposition temperature.
On Ag(100) four different structures have been identified. For two of them (namely the “square”
and the “flower” structures, both forming at 350 K) a careful combination of STM, HREELS and
XPS results and of ab-initio Density Functional Theory (DFT) calculations allowed to unravel the
details of the self-assembled layer and to understand the driving mechanisms of the self-assembly
process. In particular the “square” geometry is formed by Glu molecules in the neutral form; their
interaction with the poorly reactive Ag substrate is only due to weak van der Waals forces, while Hbonds between carboxyl groups and the formation of a OCOH—OCOH—OCOH—OCOH— cycle
at the vertex of the squares are the main responsible for self-assembling. The “flower” structure
contains both molecules in the neutral and in the anionic form, the relative position of which has
been accurately determined. An empirical model based on statistical analysis of high resolution
STM images is proposed for the other layers.
[1] M. Smerieri, L. Vattuone, D. Costa, F. Tielens, L. Savio, Langmuir 26, 7208 (2010).
[2] M. Smerieri, L. Vattuone, T. Kravchuk, D. Costa, L. Savio, Langmuir 27, 2393 (2011).
[3] I. Tranca, M. Smerieri, L. Vattuone, D. Costa, F. Tielens, L. Savio, in preparation.
* Corresponding author:
Letizia Savio, IMEM-CNR, Via Dodecaneso 33, 16146 Genova. E-mail: [email protected]
37
Organic Photovoltaic Devices with Colloidal TiO2 Nanorods as Key Functional
Components
Aurora Rizzo1*, Anna Loiudice2,3, Davide Cozzoli1,2, Giuseppe Gigli1,2,3
NNL CNR-Istituto di Nanoscienze, c/o Distretto Tecnologico, Via per Arnesano Km 5, 73100
Lecce, Italy.
2
Dipartimento di Fisica, Universita` del Salento, via Arnesano 16, I-73100 Lecce, Italy
3
CBN - Center for Biomolecular Nanotechnologies, IIT, Via Barsanti, 73010 Arnesano, Lecce, Italy
1
We report on a novel approach to integrate colloidal anatase TiO2 nanorods as key functional
components into polymer and fully inorganic photovoltaic devices by means of mild, all-solutionbased processing techniques. Recently, solution-processed of nonstoichimetric titanium oxide has
been exploited as an optical spacer, oxygen barrier and electron-transporting/hole-blocking layer in
the fabrication of conventional and inverted organic solar cell geometries [1,2]. In the inverted
geometry the preparation of such TiO2 electrodes relies on annealing at temperatures of 500°C or
greater. High-temperature fabrication steps add to manufacturing cost and energy payback time.
Steps requiring temperature treatments greater than 200°C generally rule out the use of transparent
flexible substrates desired for conformable photovoltaics. Therefore, a simple coating process of
TiO2 without the requirement of the additional annealing step is deemed necessary.
In this frame, we explore a novel strategy that enables straightforward utilization of crystalline
colloidal anatase TiO2 nanorods into both inverted and conventional solar cell geometries with
improved performances [3]. The successful integration of colloidal nanoparticles in organic solar
cells relies on the ability to remove the long chain insulating ligands, which indeed severely reduces
the charge transport. To this aim we exploit the concomitant mechanisms of UV-light-driven
photocatalytic removal of adsorbed capping ligands and hydrophylicization of TiO2 surfaces in
both solid-state and liquid-phase conditions. The inverted devices show a power conversion
efficiency of 2.3% that is ca. three times improvement over their corresponding cell counterpart
incorporating untreated TiO2, demonstrating the excellent electron-collecting property of the UVirradiated TiO2 films. The integration of UV-treated TiO2 solutions in conventional devices results
in doubled power conversion efficiency for the thinner active layer and in maximum power
conversion efficiency of 2.8% for 110 nm thick device. Moreover we demonstrated a high power
conversion efficiency of 2.5% for fully inorganic nanocrystal based solar cells on flexible
substrates, which is the highest reported for inorganic devices on plastic support.
[1] J.Y. Kim, K. Lee, N.E. Coates, D. Moses, T.Q. Nguyen, M. Dante, A.J. Heeger, Efficient
Tandem Polymer Solar Cells Fabricated by All-Solution Processing, Science, 317, 2007.
[2] L.M. Chen, Z. Hong, G. Li, Y. Yang, Recent Progress in Polymer Solar Cells: Manipulation of
Polymer:Fullerene Morphology and the Formation of Efficient Inverted Polymer Solar Cells, Adv.
Mater., 21, 2009.
[3] A. Loiudice, A. Rizzo, L. De Marco, M.R. Belviso, G. Caputo, P.D. Cozzoli, G. Gigli, Organic
Photovoltaic Devices with Colloidal TiO2 Nanorods as Key Functional Components, Phys. Chem.
Chem. Phys., DOI: 10.1039/c2cp23971j, 2012.
Corresponding author: Aurora Rizzo, NNL CNR-Istituto di Nanoscienze, c/o Distretto Tecnologico,
Via per Arnesano Km 5, 73100 Lecce, Italy. E-mail: [email protected]
38
Porphyrins and Metallo-Porphyrins on Ag(111): molecule-substrate adaptation
and interaction via induced chemical modification and metal inclusion
G. Di Santo1, 2, C. Sfligoj2, S. Blankenburg3, C. Castellarin-Cudia1, M. Fanetti1, C. A. Pignedoli3,
F. Bondino4, E.
Magnano4, A. Verdini4, A. Cossaro4, A. Morgante2, 4, D. Passerone3, L. Floreano4, and A.
Goldoni1
1Sincrotrone Trieste S.C.p.A. s.s.14 Km. 163.5, 34149 - Trieste, Italy
2Dipartimento di Fisica - Università di Trieste - via Valerio - 2, 34127 Trieste, Italy
3EMPA - Theory and atomistic simulation group, Ueberlandstr. 129, CH-8600 Dübendorf, CH
4Istituto Officina dei Materiali-CNR, Lab. TASC, s.s. 14 km 163.5, 34149 Trieste, Italy
Forming a monolayer of 2H-Tetra-Phenyl-Porphyrins on Ag(111) either by sublimation of a
multilayer at 550 K, or by annealing at the same temperature a monolayer deposited at room
temperature, we induce a chemical modification of the molecules. We observe a rotation of the
phenyl rings in a at conformation.[1] X-ray photoemission and absorption spectroscopies were used
to determine the molecular interaction and adaptation of tetraphenylporphyrins (TPP) on Ag(111)
depending on the presence or absence of a metal ion within the macrocycle. By comparing the
behavior of 2H-TPP and Co-TPP with the metalated Co-TPP obtained by evaporating Co atoms in
Ultra High Vacuum on the monolayer of 2H-TPP, it is observed that the presence of the metal ion
in the macrocycle before annealing at T > 550 K influences the adaptation of the molecules. 2HTPP molecules tend to increase as much as possible the π bonds interaction with the substrate and
therefore they subdue a temperature induced irreversible de-hydrogenation reaction in order to
rotate the phenyls parallel to the macrocycle and the substrate surface, so reducing the bond
distance. The presence of Co, instead, creates a strong bond between Co-d z states and the Ag-sp
states, that leaves the porphyrins to a greater distance from the surface with the phenyl rings rotated
by about 50° even after the annealing at T > 550 K.
[1] G. Di Santo, S. Blankenburg, C. Castellarin-Cudia, M. Fanetti, P. Borghetti, L. Sangaletti, L. Floreano,
A. Verdini, E. Magnano, F. Bondino, C. A. Pignedoli, M.-T. Nguyen, R. Gaspari, D. Passerone and A.
Goldoni. “Supramolecular engineering through temperature-induced chemical modification of 2Htetraphenylporphyrin on Ag(111): at phenyl conformation and possible dehydrogenation reactions.”
Chemistry - A European Journal, 17, no. 51, 14354 (December 2011). ISSN 1521-3765.
doi:10.1002/chem.201102268.
39
Chairman Antonio Cassinese
Parma, June 20th-22nd 2012
Poster #
Author
Affiliation
Title
Elettra
Organic-inorganic interfaces at the Materials Science
beamline, Elettra
1
Acres Robert
2
Arnaud Gaëlle
NANO
Electronic Properties Of Dye/ZnO Interfaces For
Photovoltaic Applications
3
Barra Mario
SPIN
Bias Stress effects in n-type Perylene Diimide transistors
4
Berzina Tatiana
IMEM
5
Bisti Federico
SPIN
6
Bobba Fabrizio
SPIN
Piezoreponse Force Microscopy on ferroelectric cocrystalline polymers
7
Bondino Federica
IOM
The beamline BACH: a multi-technique approach for the
study of molecular organic layers
8
Borga Elisa
IMEM
Detection of PAA covered nanoparticles by OECTs
sensors.
9
Buzio Renato
SPIN
Superconducting FeSe0.5Te0.5 thin films: a
morphological and structural investigation with scanning
tunnelling microscopy and X-ray diraction
10
Catellani Alessandra
IMEM
Functionalization of SiC(110) Surfaces via Porphyrin
Adsorption: Ab Initio Results
11
Ciccullo Francesca
SPIN
Ambipolar organic transistors based on 6T / PDI8-CN2
blend
12
Colle Renato
UniBO
Theoretical study of crystalline PDIF-CN2
13
Colonna Stefano
ISM
Tytanil-phthalocyanine self assembly on Ag(100) studied
by scanning tunneling microscopy and low energy
electron diffraction
14
Corni Stefano
NANO
Simulating charge-transfer proteins on gold surfaces
15
Cossaro Albano
IOM
Tailoring SAM on SAM formation.
Organic memristor based on the composite materials:
conducting and ionic polymers, gold nanoparticles and
graphenes
Electronic structure of AlQ3 and ErQ3 revisited using the
Heyd-Scuseria- Ernzerhof hybrid functional: theory and
experiments
40
Parma, June 20th-22nd 2012
Poster #
Author
Affiliation
Title
16
De Stefano Luca
IMM
Hydrophobin functionalized organic materials
17
Tahereh Ghane
NANO
Multi-Scale Modeling of the Optical Properties of Triplex
DNA
18
FuJii Jun
NANO
Structure and electron states of Co-Phthalocyanine
interacting with the Cu(111) surface
19
Gerbi Andrea
SPIN
Investigation of resistive switching behavior and
nanoscale electronic transport of Au/Nb-doped SrTiO3
junctions
20
Ghirri Alberto
NANO
Self-Assembled Monolayer of Cr7Ni Molecular
Nanomagnets by Sublimation
21
Gottardi Stefano
IMEM
Optimizing Picene molecular assembling by Supersonic
Molecular Beam Deposition
22
Stefano Lettieri
SPIN
Crystal Phase Dependent Photoluminescence of 6,13Pentacenequinone
23
Maglione Maria Grazia
ENEA
Comparison of ageing for different encapsulated OLEDs
on glass substrates.
24
Mattioli Giuseppe
ISM
Dye Sensitization of Zinc Oxide with Zinc
Phthalocyanines: from Isolated Molecules to
Nanostructured Molecular Aggregates
25
Mazzeo Marco
NANO
ITO-free white organic light emitting diodes based on
multi-cavity technology and PIN technology
26
Mukherjee
Subhrangsu
IOM
27
Nacci Christophe
Fritz Haber
Institute of Max
Planck Society
28
Nannarone Stefano
IOM
29
Nardi Marco Vittorio
IMEM
30
Nocera Alberto
UniRoma3
31
Olivieri Giorgia
IOM
Soft X-ray reflectivity studies of 1,4
Benzenedimethanethiol ultrathin films on Au at the C Kedge
Manipulation and spectroscopy of single phthalocyanine
molecules on InAs(111)A with a low-temperature scanning
tunneling microscope
The BEAR beamline at Elettra in the VIS-Soft X-ray region
– a tool to investigate ultra-thin organic films
Electronic properties of tetraphenylporphyrins: the role of
fluorine
Stochastic dynamics for a single vibrational mode in
molecular junctions
Investigation of 4HCB molecule by synchrotron based
techniques and theoretical DFT methods
41
Parma, June 20th-22nd 2012
Poster #
Author
Affiliation
Title
32
Pedio Maddalena
IOM
Electronic Properties of Metal Octaethylporphyrins
ordered layers mediated by Au(111) substrates
33
Pedio Maddalena
IOM
Electronic properties of Transition-Metals Porphyrins
34
Pellegrino Giovanna
IMM
TCPP anchoring process on porous nano-crystalline TiO2
layers deposited by sputtering at ~150°C on transparent
ZnO:Al substrates: effects of annealing the substrate
(500°C) before the sensitization.
35
Persano Luana
NANO
Light-emitting polymer nanofibers: next-generation
organic semiconductor nanostructures for
nanoelectronics and nanophotonics
36
Petrangolini Paolo
NANO
Metal-ion mediated surface functionalization of HOPG:
Dense SAMs assembly and soft electronic coupling
37
Pezzella Alessandro
UniNA
Efficient Visible Light-Induced Photocurrent in a Novel
Bioinspired Hybrid Bulk Heterojunction: Eumelanin-Psi
38
Pipolo Silvio
NANO
Simulating azobenzene self assembling monolayers on
gold surfaces
39
Ricciotti Laura
UniNA
Perylene derivatives functionalized with thiadiazole rings:
synthesis and electronic properties in OFET devices
40
Rosa Marta
NANO
Towards the docking of DNA on surfaces: electronic
structure of guanine and cytosine on Au(111)
41
Radivo Andrea
IOM
Nanostructured pentacene/PCBM interface for organic
solar cell
42
Terentjevs Aleksandrs
NANO
Interface electronic structures of large dipolar organic
molecules on metal substrates: computational methods
for the high- and the low-coverage regimes
42
Parma, June 20th-22nd 2012
Poster #
43
Author
Tonezzer Matteo
Affiliation
Title
IMEM
Supersonic Molecular Beam Deposition of αSexithiophene:because energy matters!
44
Verrucchi Roberto
NANO
Charge transfer at the interface between Sexithiophene
(T6) and N,N’-bis (n-octyl)- dicyanoperylenediimide (PDI8CN2) Heterostructures investigated by UPS
measurements
45
Viggiano Davide
UniMOL
Cell Biocompatibility and electrical operation in cellular
culture medium of n-type organic transistor
46
Romeo Agostino
IMEM
Monitoring drug induced cellular stress by organic
electrochemical transistors
47
Ambrosio Antonio
SPIN
Large scale micro- and nano- structuring of azobenzeneconatining polymer films
48
Coppede' Nicola
IMEM
ZnO nanostructure Functionalization for electronic, gas
sensing and photovoltaic application
49
Fortuna Sara
IOM
Structure and electronic properties of self-assembled
transition metal phthalocyanines (M=Fe,Co,Ni,Cu,Zn) on
the Au(110) surface
50
Toccafondi Chiara
CNISM
Nano-granular Thin Films As Substrates For Protein
Deposition
51
Casalini Stefano
ISMN
Organic Field-Effect Transistors as Organic Gauge for the
study of the charge injection across Self-Assembled
Monolayers
52
Bergenti Ilaria
ISMN
Magnetically Enhanced Memristor
53
Di Girolamo
Flavia Viola
SPIN /
Univ. Geneve
Organic Schottky gated heterostructures
54
Muccioli Luca
UniBO
Atomistic simulations of sexithiophene-fullerene
heterojunction
43
Parma, June 20th-22nd 2012
Poster #
Author
Affiliation
Title
55
D'Avino Gabriele
UniBO
Thin film growth of pentacene on C60 (001) from vapor
deposition simulations
56
Caporali Stefano
UniFI
Interaction of adenine with nanostructured silver surfaces
57
Liscio Fabiola
IMM
Real-time structural and electrical investigation of PDI8CN2 based OFET
58
Malloci Giuliano
IOM
Modelling morphology and electronic properties of hybrid
ZnO - oligothiophene nanostructures
59
Forrer Daniel
ISTM
Role and treatment of Van der Waals forces at the
C6H6/Ag(111) interface
60
Fratesi Guido
UniMIB
NEXAFS spectra of aromatic molecules by plane-wave
calculations
61
Roscioni Otello Maria
UniBO
Predicting the alignment of liquid crystals at a solid
surface: 5-cyanobiphenyl on cristobalite and glassy silica
surfaces of various roughness
62
Fraboni Beatrice
UniBO
Organic semiconducting single crystals as next generation
of low cost, room temperature electrical X-ray detectors
63
Fraleoni-Morgera
Alessandro
Sincrotrone
Trieste
Investigations on the response of organic semiconducting
single crystals to polarized IR spectroscopy under charge
polarization and flow
44
Abstracts
(Poster)
45
Organic-inorganic interfaces at the Materials Science beamline, Elettra
R. G. Acres1, K. C. Prince1,2, *, V. Feyer3, O. Plekan4, M. Iakhnenko1, N. Tsud5, V. Matolín5, T.
Skála1, V. Cháb6,
1
Sincrotrone Trieste S.C.p.A., Basovizza, (Trieste), Italy,
2
CNR-IOM Laboratorio TASC, Basovizza (Trieste), Italy,
3
Electronic Properties (PGI-6), Peter Grünberg Institute, Forschungszentrum Jülich GmbH,
Jülich, Germany,
4
Aarhus University, Department of Physics and Astronomy, Aarhus, Denmark,
5
Charles University, Faculty of Mathematics and Physics, Prague 8, Czech Republic,
6
Institute of Physics, Academy of Sciences of the Czech Republic, Prague 6, Czech Republic.
*
Corresponding author: [email protected]
The Materials Science beamline at the Italian synchrotron light source Elettra has been used
to investigate a series of organic interfaces with metals, oxides and semiconductors [1-9]. The main
focus has been on biomolecules adsorbed on gold single crystals, but there have also been
investigations employing other substrates such as copper, oxides, nanoparticles and semiconductors.
Samples have been prepared by evaporation in vacuum and by wet chemical methods. The main
techniques applied are valence and core level photoemission, and x-ray absorption at the carbon,
nitrogen and oxygen edges. Using these techniques, it is possible to gain information about the
orientation and chemical bonding of organic molecules to surfaces.
As an example, small peptides of the amino acids histidine and glycine adsorbed on Au(111)
were studied in the work reported in reference 3, and it was possible to develop the schematic
model shown in the figure. The molecules are bound to the surface via the carboxylic acid and
imidazole side chains. The peptide bond and amino group of the glycine residue do not interact
significantly with the surface.
The Materials Science beamline is a user facility with open access to the scientific
community [10]. Some of the experimental possibilities available to users will be illustrated.
Figure 1, from ref. 3. Schematic bonding of histidine (His) and glycine (Gly) peptides with a
Au(111) single crystal.
[1] V. Feyer et al, J. Phys. Chem. B 112 (2008) 13655-13660.
[2] V. Feyer et al, Phys. Rev. B 79 (2009) 155432.
[3] V. Feyer et al, Langmuir 26 (2010) 8606.
[4] V. Feyer et al, J. Phys. C 114 (2010) 10922
[5] V. Feyer et al, Surf. Sci. 605 (2011) 361
[6] O. Plekan et al, Surf. Sci. 601 (2007) 1973-1980.
[7] O. Plekan et al, J. Phys. Chem. C 114 (2010) 15036
[8] O. Plekan et al, Surf. Sci. 606 (2011) 435.
[9] Z. Majzik et al, J. Phys. Chem. C 115 (2011) 21791.
[10] http://www.elettra.trieste.it/UserOffice/
46
Electronic Properties Of Dye/ZnO Interfaces For Photovoltaic Applications
G. F. Arnaud*, V. de Renzi*, U. del Pennino*
University of Modena and Reggio Emilia - Physics Department , Modena, Italy
*Centro S3, CNR-Istituto di Nanoscienze, I-41125 Modena, Italy
Dye-sensitized solar cells (DSSCs) represent a particularly promising approach to the direct
conversion of light into electrical energy at low cost and with high efficiency. Indeed adsorption of
molecular dyes is used to tailor the optical response of metal-oxide materials (ZnO, TiO2), making
them photoactive in visible range and thus useful as photoanodes in dye-sensitized solar cells.
Catechol adsorbed on metal oxides has received considerable attention as a model dye-sensitizer
and as a possible stable anchoring group to bind larger metal-based organic dyes. 1,2,3
Key issues to be investigated in this context are both the microscopic picture of the interface
structure and the detailed mechanisms of energy level alignment. In this work we focus on the
interface of two catechol-like molecules (1,2-dihydroxybenzene, 4-nitrocatechol) with a ZnO(1010) non-polar single crystal surface.
The adsorption mechanism is investigated with XPS and HREELS (High Resolution Electron
Energy Loss Spectroscopy) techniques showing that a full monolayer of intact molecules is
obtained for both moieties. The interfacial electronic properties4 has studied by XPS and UPS:
Energy level alignment of molecular filled states, adsorption induced work function variation and
band bending at the interface has been measured. The band bending is evaluated taking XPS spectra
at different emission angle, in this way it has been possible to study the depth profile of band
bending. UPS valence band measurements clearly show that in both systems the HOMO lies at the
same energy position relative to Valence Band, within the ZnO gap.
Corresponding author: Gaelle Arnaud
Università degli Studi di Modena e Reggio Emilia
Dipartimento di Fisica Via Campi, 213/A 41125 Modena
Tel.: 0592055038 e-mail: [email protected]
1 A. Hagfeldt et al., Chem. Rev., 110 (2010) 6595. 2 U. Diebold et al., Appl. Surf. Sci., 237 (2004) 336. 3 Li et al. J. Am. Chem. Soc. 131 (2009) 980. 4 P. Zurcher et al. Vac. ScI. Technol. 1 (1983) 695. 47
Bias Stress effects in n-type Perylene Diimide transistors
M. Barra1*, F. V. Di Girolamo1, F. Ciccullo1, N. A. Minder2, I. Gutierrez-Lezama2, Z. Chen,3 A.
Facchetti,3 A. Morpurgo2, A. Cassinese1
1
CNR-SPIN and Dep. of Physics Science, University of Naples, Piazzale Tecchio 80, Naples Italy
DPMC and GAP, University of Geneva, 24 Quai Ernest-Ansermet, CH-1211 Geneva, Switzerland
3
Polyera Corporation, 8045 Lamon Avenue, Skokie, IL 60077 (USA)
The bias stress (BS) phenomenon is the main source of operational instability in the organic fieldeffect transistors (OFET) and represents the most serious obstacle to their commercial introduction
[1]. This effect, which basically consists in a continuous time decay of the drain-source (IDS) current
when the transistors are driven in the accumulation regime for a prolonged time, has been widely
investigated for p-channel OFET. Conversely, in n-channel transistors, it has so far received little
attention and few experimental data are currently available.
In this contribution, we report on the BS effects occurring in both thin-film and single-crystal
transistors based on Perylene Diimide molecules, being today among the most interesting n-type
semiconducting compounds thanks to their highly robust charge transport properties also in air [2].
Firstly, we discuss the BS phenomenon in thin-film devices fabricated by evaporating PDI8-CN2
and PDIF-CN2 molecules on both bare and hexamethyldisyloxane (HMDS)-treated SiO2 gate
dielectrics. Our results indicate that, in these devices, the chemical properties of the interface
between dielectric barrier and semiconductor play a major role in the BS effect, suggesting also the
possibility that its physical origin can be related to a diffusion process in the dielectric barrier by
negatively charged ionic species, electrochemically generated through reactions involving water
and oxygen. When the BS effect was analyzed in PDIF-CN2 single-crystal transistors with Cytop
gate dielectric, we found that the amount of stress is very small as compared to all (p-channel)
organic transistors studied in the past [3]. The IDS(t) decrease in these OFET is of only 10% in air
even when they are driven in the
accumulation regime for an entire week
(Fig.1). By fitting the experimental IDS(t)
VDS=10V, VGS=80V
1.00
curves with the stretched exponential model,
the characteristic time constants τ are found to
0.98
be higher than 109 sec, being two orders of
1.00
magnitude larger than the best values reported
0.96
0.98
previously for p-channel OFET. Moreover,
0.96
we observe that, for both thin-film and single0.94
0.94
crystal transistors, the BS effect tends to
0.92
0.92
saturate in vacuum for stressing periods larger
0.90
0 1 2 3 4 5 6 7 8
Days
than 1-2 days. Although, n-type OFET have
0.90 -1
0
1
2
3
4
5
6
been traditionally considered to be more
10
10
10
10
10
10
10
10
sensitive on charge trapping process, our
TIME (S)
results highlight that a right combination of
Fig.1 Single-crystal PDIF-CN2 transistors: IDS(t)/I0
materials allows almost completely cancelling
measured in air for about 1 week. The dashed lines
the BS effect in these devices.
are the best fits to the stretched exponential model.
IDS/I0
IDS/I0
2
Corresponding author: Mario Barra ([email protected]) - CNR-SPIN and Dep. of Physics Science, University
of Naples, Piazzale Tecchio 80, Naples Italy
References: [1] H. Sirringhaus, Reliability of Organic Field-Effect Transistors, Adv. Mater. 21, (2009) 3859. [2] B. A.
Jones, A. Facchetti, M. R. Wasielewski, T. J. Marks, J. Am. Chem. Soc. 129, (2007) 15259. [3] M. Barra, F. V. Di
Girolamo, N. A. Minder, I. Gutierrez-Lezama, Z. Chen, A. Facchetti, A. F. Morpurgo, A. Cassinese,, Appl. Phys. Lett.
100, 133301 (2012)
48
Organic memristor based on the composite materials: conducting and ionic
polymers, gold nanoparticles and graphenes
1
Tatiana Berzina1 and Victor Erokhin1
CNR-IMEM, Parco Area delle Scienze 37/A - 43124 Parma, 43100 Italy
Organic memristor [1] is a solid state device with electronic conductivity depending on the
ionic charge that has passed through it. This property is rather similar to the feature of biological
synapses and allows to consider the device as a key element for the circuits capable of Hebbian type
of learning [2].
Thin polyaniline (PANI) layer is deposited onto insulating support with 2 metal (Cr) electrodes.
Lithium salt doped polyethylene oxide, used as solid electrolyte, is deposited in the central part of
the PANI layer and a silver wire is attached to it. Working principle of the device is based on the
strong variation of PANI conductivity in the reduced and oxidized state. Application of the positive
voltage higher than the oxidation potential results in the increase of the memristor conductivity,
while the application of any negative potential (reduction potential of PANI is about +0.1 V) results
in the increase of its resistance.
The aim of the present study was the fabrication of polyaniline (PANI) – AuNPs composite
material, resulting in the formation of Schottky barriers acting as thershold element. This task is
connected to the more general task – realization of bio-inspired adaptive networks.
Characterization of the synthesized complex materials and the structures with particular reference to
their morphology and electrical properties were done.
The best results were obtained with the use of 2-Mercaptoethanesulfonic acid stabilized gold
nanoparticles.
The electrical characterization has clearly shown a nonlinear electrical behavior of the formed
composite. The suppression of the conductivity in the low voltage range is connected to the
presence of gold nanoparticles in the sample, sparsely embedded in the matrix of PANI.
We have prepared and checked also memristive devices containing graphenes in active zone.
Electrical characterization of such devices has demonstrated a pronounced hysteresis in the positive
voltage range that can be associated with charge trapping by graphene sheets similarly to the case of
gold nanoparticles.
[1]
[2]
Erokhin, V., Berzina, T., and Fontana, M.P. 2005. Hybrid electronic device based on
polyaniline-polyethylene oxide junction. J. Appl. Phys. 97, 064501.
Hebb, D.O. 1949. The organization of Behavior: a neuropsychological theory. Wiley and Sons,
New York.
Corresponding author:
Tel. (0521) 90 52 51; e-mail:
49
[email protected]
Electronic structure of AlQ3 and ErQ3 revisited using the Heyd-ScuseriaErnzerhof hybrid functional: theory and experiments
F. Bisti1 *, A. Stroppa2, M. Donarelli1, S. Picozzi2 and L. Ottaviano1,2
1
Dipartimento di Fisica, Università dell'Aquila,Via Vetoio 10, 67100, L'Aquila, Italy
2
CNR-SPIN L'Aquila,Via Vetoio 10, 67100, L'Aquila, Italy
Tris(8-hydroxyquinolinato)aluminium(III) (AlQ3) is one of the most studied organic molecules, due
to its application as an active layer in OLED systems and, recently, as a nonmagnetic conducting
layer in spin valves. Tris(8-hydroxyquinolinato)erbium(III) (ErQ3) is important for possible
applications in the field of optical silica fiber amplifiers and OLED devices due to the ability to
emit in the IR range of optical telecommunication interest.
In this work, the electronic structure of these two molecules, grown by vacuum thermal evaporation
on inert substrates, have been studied by core level and valence band photoemission spectroscopy
using laboratory sources. Experimental data have been compared with Density Functional Theory
calculations, using the screened hybrid Heyd-Scuseria-Ernzerhof functional (HSE) [1].
For AlQ3, calculations were also used for the interpretation of x-ray absorption and emission
spectra reported in the literature.
The agreement between experiment and theory is very good and this work can be considered an
important benchmark of the HSE functional for the interpretation of the electronic structure of
organic molecules [1]. Furthermore, by means of a detailed comparison between the two valence
bands, we have been able to disentangle the role played by the central metal atom in the molecular
electronic properties. Finally, improvements of hybrid functional treatment for Erbium 4f orbitals
have been discussed.
[1] F. Bisti, A. Stroppa, M. Donarelli, S. Picozzi and L. Ottaviano Phys. Rev. B 84 (2011) 195112
*Corresponding author: [email protected]
50
Piezoreponse Force Microscopy on ferroelectric co-crystalline polymers
F. Bobba (1), A. Scarfato (1), A.M. Cucolo (1), C. Daniel (2), C. Rufolo (2), G. Guerra (2)
1: SPIN-CNR and Dipartimento di Fisica E. R. Caianiello, Università degli Studi di Salerno, Italy
2: Dipartimento di Chimica e Biologia, Università degli Studi di Salerno, Italy
In the last years, a new class of ferroelectric hybrid materials based on syndiotactic polystyrene (sPS) promises to be of great interest for future developments of plastic electronics. Recently, it has
been demostrated that the ε and δ co-crystalline phases of s-PS, although apolar, are able to absorb
high-polarity guests from solutions in suitable carrier-solvents, leading to highly stable apolarhost/polar-guest clathrates. In this study, the ferrolelectric response of ε-clathrate and δ-clathrate
with 4-nitroanilin (NA), a small guest of high polarity (6.2 D), has be investigated by Piezoresponse
Force Microscopy (PFM) and then compared with the well known ferroelectric response of
poly(vinylidene-fluoride-trifluoroethylene) P(VDF-TrFE)-copolymer film. Indeed, the imaging and
dynamics of the piezoelectric response is perhaps the most direct method of probing polarization at
the nanoscale. In our experiments, we were able to observe a local hysteretic behavior at different
points in both the ε and δ (NA) s-PS film surfaces, by measuring the piezoresponse while sweeping
a continuous voltage bias. The measured coercive bias of the hysteresis loops resulted highly
variable in the range 0.7-0.2 V from point to point of the film surface possibly related to local
variations in the s-PS film thickness of nominal 0.1 μm value and/or to different polarization
anisotropy within the sample. In addition to this, on large areas of the order of 100 nm2, different
polarization states have been imposed by applying a dc voltage between the AFM tip and a
conductive bottom layer while scanning in contact mode. This writing procedure was clearly
observed through the PFM image contrast. Evidence for memory behavior of the co-crystalline sPS samples was confirmed by the ability to re-write the films, simply by reversing the polarity of
the external field and by imposing opposite polarities in different film regions. For the δ clathrate
phase, in absence of external fields, the written images are lost through an exponential intensity
decay with characteristic time costant of about 60 min. We remark here that such ferroelectric
behavior was never observed for the γ s-PS amorphous phase containing a similar amount of NA
molecules randomly dispersed inside the polymer. In summary, our study confirms that
ferroelectric hybrid polymer materials can be obtained by crystalline phases whose polarity is given
by low-molecular-mass guest molecules rather than by polymer chain polarity as in P(VDF-TrFE)copolymer films.
51
The beamline BACH: a multi-technique approach for the study of molecular
organic layers
F. Bondino* and E. Magnano*
IOM­CNR,
TASC
laboratory,
S.S.
14
km
163.5,
Area
Science
Park,
34149
Basovizza
(Ts),
Italy
M. Yabloskikh, L. Stebel
Sincrotrone
Trieste,
S.S.
14
km
163.5,
Area
Science
Park,
34149
Basovizza
(Ts),
Italy
M. Malvestuto, V. Capogrosso, F. Parmigiani
Sincrotrone
Trieste,
S.S.
14
km
163.5,
Area
Science
Park,
34149
Basovizza
(Ts),
Italy,
Department
of
Physics,
University
of
Trieste,
via
A.
Valerio
2,
34127,
Trieste,
Italy
IOM­CNR,
TASC
laboratory,
S.S.
14
km
163.5,
Area
Science
Park,
34149
Basovizza
(Ts),
Italy
The BACH beamline (Beamline for Advanced diCHroism) is an undulator beamline of the Istituto
Officina dei Materiali-Consiglio Nazionale delle Ricerche, which operates at Elettra, in close
collaboration with Sincrotrone Trieste S.C.p.A.
The beamline offers a multi-technique approach for the investigation of the electronic, chemical,
structural, magnetic and dynamical properties of solid surfaces, interfaces, thin films and solid
samples, including molecular organic compounds, in the UV-soft x-ray photon energy range (351600 eV) with selectable light polarization (linear horizontal and vertical, circular), high resolving
power (20000-6000) and also time resolution (70 psec).
During its operation, the BACH beamline has found many applications in the study of selfassembled molecular layers, oriented molecular growth, molecular anchoring, organics on transition
metal oxides, magnetic organic overlayers, and complex metallo-organic architectures.
The number of techniques and spectroscopy methods available at this beamline is unique. Angleresolved and fast (<350 msec/specrum) high-resolution photoemission can be performed from UV
to soft X-rays. X-ray absorption spectroscopy can be performed in total and partial fluorescence
yield and total and partial electron yield with different detectors (drain current, photodiode,
channeltron, MCP, electron analyser, fluorescence grating spectrometer), different environments (in
UHV and liquid cells, under very high magnetic fields and very low temperatures) and different
time scales down to subnssec. The samples (thin metallic and oxide films, molecular layers,
metallo-organic architectures) can be prepared and grown in situ.
A brief overview of the recent upgrades of the beamline will be presented, focusing in particular on
the installation and first results of the a new VG-Scienta R3000 analyser for fast UPS/XPS/ARPES
and XPD, the installation of the new UHV 6.5 Tesla 1.5 K cryomagnet endstation for x-ray
magnetic circular dichroism and time-resolved XMCD and the first results of the new sub nsec
time-resolved laser pump-synchrotron probe x-ray absorption endstation which has been recently
open to users.
52
Detection of PAA covered nanoparticles by OECTs sensors.
T. Toccolia, E. Borgaa, H. Blonda, D. Maniglioc, L. Minatib, C. Fasolia, M. Polaa, C. Corradia and S.
Iannottaa
a
IMEM-CNR Trento, Istituto Materiali per Elettronica e Magnetismo Via Alla Cascata 56/C, 38123
Povo di Trento, Italy
b
Plasma, Advanced Materials and Surface Engineering PAM-SE FBK, Via Sommarive 18, 38123
Povo di Trento, Italy
c
University of Trento, Department of Materials Engineering and Industrial Technologies and
Biotech Research Center, 38123 Trento, Italy
Normalized Response (%)
The use of organic materials has great importance for several topics such as photonics [1],
photovoltaics [2] and in particular for sensors [3]; such materials in fact are biocompatible with
organic systems and permit the realization of low cost devices [3]. The idea is trying to discriminate
different functionalizations on NPs and the quantity of polymer loaded on them. This gives
information about the quantity of drugs that could be loaded on the polymeric shells and to follow
dynamic processes such as the stability of the NPs at different conditions and the release of the
loaded drug. The devices are realized on a glass substrate with ink-jet printing methods, using a
micro-syringe and micro-positioning system. The working principle of the OECTs is based on the
doping and dedoping of the drain-source channels due to
the ions dissolved in the solution in relation to the gate and
drain-source potentials applied. The current modulation
(the ratio between the current difference when the gate is
off and on) describes the current variation [4]. Adding to
the solution the organic polymer PAA or the nanoparticles
covered with the same polymer, the current modulation
changes. We have defined the normalized response (NR) in
c (mg/ml)
order to evaluate this modulation variation. At different
Fig. 1: a) NR at different PAA concentration. The
concentrations
correnspond different NR values with a
detection limit and sensitivity in the case of PAA
-4
linear trend (Fig.1). Fitting the data we calculate the
was respectively (7.6 ± 0.8) 10 mg/ml and 4.0 ±
0.4 NR/(mg/ml) with 0.4V at the gate and (2.7 ±
detection
limit and the sensitivity of the system. The
0.3)10-3 NR/(mg/ml) and 3.8 ± 0.2 mg/ml with 0.5
realized OECTs show a good reproducibility and stability
V. b) The same plot in the case of using Gold NPs
covered with a PAA shell. The detection limit and
which permitted to use them as sensors in the analysis of
the sensitivity in this case are: (1.8 ± 0.2) 10-4
the charged polymer PAA and of the nanoparticles
mg/ml and 4.0 ± 0.3 NR/(mg/ml) with 0.4V at the
gate, (8.1 ± 0.4) 10-5 mg/ml and 1.93 ± 0.08
concentrations, because we have observed the correlation
NR/(mg/ml) with 0.5 V.
between modulation current and concentration both for
PAA and for PAA covered nanoparticles. This results are at
the basis for further works about the detection of drugs loaded on the polymeric shell and the study
the drug delivery.
10
8
4
2
0
1E-4
10
(a)
1E-3
0.01
0.1
1
8
6
4
2
0
1E-5
[1]
[2]
[3]
[4]
Vg = 0.4V
Vg = 0.5V
6
(b)
1E-4
1E-3
0.01
0.1
1
R. Capelli, S. Toffanin, G. Generali, H. Usta, A. Facchetti and Michele Muccini, N. Mat. 9 (2010) 496-503.
B. P. Rand, J. Genoe, P. Heremans and J. Poortmans, Prog. Photovolt: Res. Appl, 15 (2007) 659-676.
J. T. Mabeck, G. G. Malliaras, Anal. Bioanal. Chem., 384 (2006) 343-353.
D. J. Macaya, M. Nikolou, S. Takamatsu, J. T. Mabeck, R. M. Owens, G. G. Malliaras, , Sens. Actuators B, 123
(2007) 374-378.

Corresponding author: Address: IMEM-CNR-FBK Trento, Instituto Materiali per l’Elettronica e Magnetismo, via alla
Cascata 56/C, 38123 Povo di Trento, Italy; Tel: +390461314830; Fax: +390461314875;
E-mail address: [email protected] (E. Borga)
53
Superconducting FeSe0.5Te0.5 thin films: a morphological and structural
investigation with scanning tunnelling microscopy and X-ray diraction
Andrea Gerbi a, Renato Buzio a, Emilio Bellingeri a, Shrikant Kawale a, DanieleMarrè a,b, Antonio
Sergio Siri a,b, Andrea Palenzona c, and Carlo Ferdeghini a
a
CNR-SPIN, Corso Perrone 24, 16152 Genova, Italy
Dipartimento di Fisica, Università degli Studi di Genova, Via Dodecaneso 33 Italy
c
Dipartimento di Chimica, Università degli Studi di Genova, Via Dodecaneso 31 Italy
b
It is so far established that high quality, epitaxial FeSexTe1-x thin films can be grown by pulsed laser
deposition (PLD) and that tensile and compressive stresses build up during thickening of the film
and affect the critical temperature (Tc) in a remarkable way [1-3]. Accordingly, a complex
phenomenology has been reported and Tc values up to 21 K have been observed. It is therefore
interesting to address the mechanisms of stress formation and release during the deposition of such
materials. Similar studies have been challenged for metal and semiconductor thin films, where a
detailed investigation of the growth and surface structure allowed an exploration of the relationship
between morphology, stress and transport properties [4]. In this context it has been shown that the
deposition rate effectively controls the amount of strain accumulated during the growth process [5].
Here we report a low-temperature (4.8K) scanning tunnelling microscopy (STM) and x-ray
diffraction (XRD) investigation of 150 nm thick FeSe0.5Te0.5 superconducting films epitaxially
grown by PLD. We describe surface morphology and discuss its relationship with film structure and
Tc for two deposition rates. Samples with critical temperature Tc above the bulk value (>16 K)
show large atomic terraces, and a square lattice of periodicity 3.8 A associated with the Se/Te
surface termination. Differences in the height coordinate of the chalcogenide atoms are clearly
visible at the atomic level. On the contrary, samples with lower Tc (11 K) show hillocks generated
by a spiral surface growth driven by threading dislocations of screw character. A comparative x-ray
diffraction analysis reveals differences of compressive strain for the two classes of specimens.
Variations in the deposition rate are found to affect film growth and inner strain, which ultimately
tune Tc [6].
[1] Bellingeri E. et al., Appl. Phys. Lett. 96 102512 (2010)
[2] Wang M. J. et al Phys. Rev. Lett. 103 117002 (2009)
[3] Huang S. X. et al Phys. Rev. Lett. 104 217002 (2010)
[4] Springholtz G. and Wiesauer K. 2002 Phys. Rev. Lett. 88 015507 (2002)
[5] Tello J. S. et al Phys. Rev. Lett. 98 216104 (2007)
[6] Gerbi et al. Supercond. Sci. Technol. 25 012001 (2012)
Andrea Gerbi,
CNR-SPIN Corso Perrone 24, 16152 Genova
e-mail: [email protected]
cell: 3406709619
54
Functionalization of SiC(110) Surfaces via Porphyrin Adsorption: Ab Initio
Results
Alessandra Catellani† and Arrigo Calzolari‡
† CNR-IMEM, Parco Area delle Scienze, 37A, I-43100 Parma, Italy
‡ CNR-NANO, Istituto Nanoscienze, Centro S3, I-41125 Modena, Italy
We investigate molecular sensitization of the nonpolar SiC(110) surface by means of density
functional simulations. We focus on aromatic fragments up to a full porphyrin molecule, in view of
potential application in bio- sensors and devices. Our results reveal a relatively low affinity between
aromatic rings and the surface, even when dispersion forces are explicitly taken into account. The
unique important difference is the pyrrole ring: pyrrole is found to experience an exothermic
reaction that leads to stable hybrid interfaces. We propose different experimental techniques to
compare with our theoretical predictions.
55
Ambipolar organic transistors based on 6T / PDI8-CN2 blend
F. Cicculloa*, A.Brunob,c, S.A. Haquec, A. Cassinesea
Dipartimento di Scienze Fisiche, Università degli studi di Napoli “Federico II, Napoli Italy
b
Centro di Ricerca ENEA, Portici,Italy
c
Chemistry Department, Imperial College London, London UK
a
In the past decades great advancements have been made in the development of organic-material
based devices, such as field-effect transistors (FETs), light-emitting diodes, solar cells, organic
memories. These devices are technologically interesting because they could serve as the main
component in low cost, large-are flexible microelectronics and hybrid electronics.
Ambipolar charge transport is a desirable property for organic semiconductors as it enables the
fabrication of complementary logic circuits. Blends of n- and p-channel materials are demonstrated
as a good approach to producing ambipolar organic field effect transistors with tunable electrical
characteristics. This method is easier and faster feasible than the bilayer approach because there is
no need to deposit two layers on top of each other.
We have been working on fabrication and characterization of field-effect transistor based on a
coevaporated film of sexithiophene (6T) and N,N’ –bis(n-ctyl)-x:y, dicyanoperylene- 3,4:9, 10-bis
(dicarboximide), PDI8CN2. 6T is known as a good hole-transporting material, and PDI8CN2
belongs to a class of perylene di-imide derivates, which are considered to be among the most
important n-type organic materials. The two materials were chosen because the positions of the 6T
highest occupied molecular orbital (HOMO) and PDI8CN2 lowest unoccupied molecular orbital
(LUMO) allow a good injection of holes and electrons from the same electrode.
Bilayer FETs based on these two materials have been already studied and they have shown
ambipolar behaviour but blend approach has not been reported before, least to our knowledge.
Our device active layer consisted of a vacuum-sublimed bulk heterojunction composed of
6T/PDI8CN2 ratios of 1:10. Atomic force microscopy and X-ray diffraction analysis indicate that
the morphology of the film is rather inhomogeneous, dominated by large clusters. Then 6T and
PDI8CN2 do not mix on molecular scale in the co-evaporated thin films, but more probably form an
interconnected network of micro- and nano- crystalline mixed clusters. The presence of joint
structures has been confirmed by time resolved and steady state optical spectroscopy measurements.
The transistor exhibited a pronounced ambipolar behaviour in the output and transfer characteristics
and very high conductivity. Despite the very low p-type material percentage in the device, the hole
current is much higher than that shown by 6T single layer transistors with a comparable or higher
amount of material. Then the electron and hole conductivity could be tuned over a wide range by
changing the composition of the thin film, so as to tailor the device functionality.
*Electronic-mail: [email protected]
56
Theoretical study of crystalline PDIF-CN 2
Renato Colle1,2, Giuseppe Grosso2,3, Layla Martin-Samos4
1
DICAM University of Bologna, via Terracini,28 40136 Bologna, Italy
2
DF University of Pisa, Largo Pontecorvo,3 56127 Pisa, Italy
3
NEST-Istituto di Nanoscienze-CNR, Pz. San Silvestro,12 56127 Pisa, Italy
4
CNR-IOM Democritos, via Bonomea,265 34136 Trieste, Italy
We investigate structural, electronic and optical properties of PDI-FCN 2 which has been
demonstrated recently as high-mobility, ambient stable, n-type organic single crystal material for
organic field effect transistors (OFET). Our study is based on DFT with inclusion of van der Waals
interactions for what concerns ground state properties of the system, and on the first-principles
many-body GW-BSE (Bethe Salpeter) theory for the treatment of its excitation properties.
From the optimized geometrical structure obtained for the PDIF-CN 2 single crystal, we evaluate the
X-spectrum which favorably agrees with existing measured spectra on films.
The electronic structure evaluated for the optimized geometry highlights strong anisotropy in the
electronic bands curvature which roots at the molecular packing in the crystal, and is responsible of
the charge mobility anisotropy. The evaluated band structure provides a sound basis for the
interpretation of the optical measured spectra in terms of allowed interband transitions. We
demonstrate that crystalline PDIF-CN 2 is a direct-gap semiconductor with onset of the optical
transitions at the Brillouin zone border. Many-body effects are also included.
57
Tytanil-phthalocyanine self assembly on Ag(100) studied by scanning tunneling
microscopy and low energy electron diffraction
S. Colonna, F. Ronci, A. Cricenti, A. Amore Bonapasta, G. Mattioli, F. Filippone, G. Pennesi,
G. Rossi, A.M. Paoletti
CNR Istituto di Struttura della Materia, Rome, Italy
The interface structure is of paramount importance in tailoring the optical and electronic properties
of the hybrid organic/inorganic heterostructures, such as Phthalocyanine (Pc) film deposited on a
metal [1-3].
Here we present a Scanning Tunneling Microscopy (STM) and Low Energy Electron Diffraction
(LEED) investigation of titanyl-phthalocyanine (TiO-Pc) molecules deposited on Ag(100). The
experimental results combined with Density Functional Theory (DFT) calculations allow a
complete characterization of the TiO-Pc/Ag(100) interface.
The TiO-Pc molecule presents a non-planar structure with the titanyl group pointing outward with
respect to the macrocycle plane. Such molecule is thus expected to interact with the substrate in two
different ways: with the TiO group toward the surface or away from it.
At very low coverage (isolated molecules) two different structures were detected by STM
measurements at low temperature (5 K), attributed to molecules adsorbed with the TiO group
pointing outward or inward with respect to Ag surface. The TiO-Pc molecules adsorbed with the
TiO group toward the surface show two possible orientations (±30°) with respect to the Ag [011]
direction, whereas the molecules pointing upwards tend to align along the [011] direction.
Increasing the TiO-Pc amount deposited on the Ag(100) surface the molecules tend to organize to
form an ordered film. Two distinct domains of the organic overlayer are detected by LEED and
STM on the surface, presenting a square lattice rotated ±8° with respect to the Ag(100) surface
lattice, in agreement with DFT modeling. STM measurements showed that the orientation of the
single molecules in the overlayer changes from ±30° to ±27°, regardless the adsorption side of the
interacting molecule. Two interesting features are observed in the organic layer: i) the domains are
formed by both kind of molecules with an apparent random arrangement; ii) in the two differently
oriented domains the TiO-Pc molecules present opposite chiral structures. At coverage close to the
complete monolayer (≈80%) the regions between the ordered domains present high molecular
mobility even at 80K, the molecules pointing upwards showing higher mobility. When the organic
layer reaches a complete monolayer the surface presents extensive domains limited by the substrate
terraces.
[1] L. Bogani, W. Wernsdorfer, Nature Materials 7 (2008) 179
[2] G. J. Hutchings, Annu. Rev. Mater. Res. 35 (2005) 142
[3] F. Rosei et al., Science 296 (2002) 328
Corresponding author: S. Colonna e-mail: [email protected]; Tel. +39 0645488163; Fax +39 0645488153
58
Simulating charge-transfer proteins on gold surfaces
1
M. E. Siwko,1,2 S. Corni2*
Department of Physics, University of Modena and Reggio Emilia, Modena, Italy;
2
*Center S3, CNR-Institute of Nanoscience, Modena, Italy.
Electron-transfer proteins immobilized on metal surfaces are important in technological fields such
as biosensors, enzymatic biofuel cells and biomolecular electronics. In particular, it has been
demonstrated that the protein functionality is maintained in several cases, although the latter may be
somewhat modified by the interaction with the surface. Our group is developing and applying
computational tools to simulate the interaction between proteins and inorganic surfaces. Within this
framework, we have simulated by classical molecular dynamics entire ET proteins immobilized on
gold surfaces. Thanks to these simulations, we could rationalize experimental ET trends that have
been measured for mutants of cytochrome C on gold electrodes. In particular, we show that
relatively small structural rearrangements taking place for the proteins at the interface can have
profound effects on the protein ET ability, even when the folding of the protein is conserved.
*E-mail: [email protected]
59
Tailoring SAM on SAM formation.
A. Cossaro1*, D. Cvetko1,2, G. Kladnik1,2, A. Verdini1, A. Morgante1,3, L. Floreano1
1
Laboratorio Nazionale TASC, CNR-IOM, S.S. 14 Km 163.5 34012 Trieste, Italy
2
Department of Physics, University of Ljubljana, Ljubljana, Slovenia
3
Department of Physics, University of Trieste, Trieste, Italy
The possibility to control the structural and electronic properties of the first molecular layer of an
organo-metallic interface is a major task of nano-device engineering. A promising route is to
interpose a Self Assembled Monolayer (SAM) between the molecules or the proteins and the
substrate. This allows to tune both the morphology and the electronic properties of the interface and
therefore to better control the characteristics of the device.
We have recently experimented a novel procedure for the growth of a metal-SAM-organic film
architecture, entirely developed under Ultra High Vacuum (UHV) conditions, with the aim to
enhance the control on the hetero-organic interface. The procedure relies on the exploitation of the
amino-carboxylic chemical affinity. A metal surface ( Au(111) ) is first functionalized by a NH2terminated SAM. A monolayer of COOH-terminated molecules is then grown on top. The NH2COOH interaction drives the morphology of the hetero-organic junction. Each carboxylic molecule
is anchored to one amino-termination of the SAM. We have described this process starting with
simple small molecules. The amino-functionalization of the metal surface has been obtained with
the growth of a SAM of cysteamine (CA), which has been characterized by means of X-ray
Photoemission Spectroscopy (XPS)[1]. A monolayer of Benzoic Acid (BA) has been then deposited
on top. By means of XPS it has been shown that the formation of a hydrogen bond between the
COOH and the NH2 groups takes place[2]. The polar orientation of the BA molecules has been
determined by means of absorption spectroscopy (NEXAFS). We have then investigated the role of
the number of carboxylic groups per molecule. We monitored the anchoring process for a 2carboxylic molecule (terephthalic acid, TPA) and showed that a bi-dentate linking is formed. In
general, this indicates how the SAM-molecule interaction can be tailored by selecting the proper
number of functional groups, which determines the molecules adsorption geometry as well.
In conclusion, we present a method for the growth of complex organic structures where each
carboxylic molecule is linked to one molecule of the SAM through a defined and reliable
interaction. Our approach opens to the appealing perspective to describe the electronic transport
properties of the system as the sum of the transport properties of the single aminocarboxylic
molecular junction, which can be in principle determined by means of STM-based spectroscopy.
References
[1] The Journal of Physical Chemistry C 2010, 15011-15014.
[2] The Journal of Physical Chemistry Letters 2011, 2, 3124−3129.
Corresponding Author: Albano Cossaro, CNR-IOM, Basovizza S.S. 14 Km 163.5, 34149 Trieste, Italy
[email protected]
60
Hydrophobin functionalized organic materials
Luca De Stefano, Ilaria Rea, Sara Longobardi*, Paola Giardina*
IMM-CNR, Via P. Castellino 111, 80131, Napoli, Italy
*Dept. of Chemistry, University of Naples “Federico II”, Via Cinthia, 80100, Napoli, Italy
A new family of hybrid organic-biologic devices can be designed and realized by using
biomolecules extracted by natural organisms. DNA single strands, proteins, and enzymes are by far
used in many successful applications, mainly in the diagnostic and monitoring fields. Beyond
biosensors, biomacromolecules can be directly used to change physical and chemical properties of
organic materials. In this comm unications, we re port our newest results about the modification of
organic and inorganic surfaces by using hydrophobins, small and cysteine-rich fungal proteins
produced in the hyphal cell walls.
We have ch aracterized from chemical and optical points of view the self -assembled biofilm of the
class I hydrophobin from the fungus Pleurotus ostreatus casted by solution deposition on flat and
porous surfaces. To his aim, experimental procedures and optical models have been developed in
spectroscopic ellipsometry, water contact angle, infrared spectroscopy, and atomic force
microscopy.
The nanometric biofilm of hydrophobin proteins can protect the surfaces from chemical dissolution,
such those used in the wet etch processes. Due to the amphiphilic nature of the biofilm, the
wettability of surfaces can be turned from hydrophobic to hydrophilic and viceversa. The
hydrophobin biofilm can also act as an active substrate to immobilize other biomolecules such as
proteins, peptides, enzymes and so on.
The results obtained in the bio-modification of such organic based surfaces and structures are very
promising for the utilization of the hybrid organic-biologic interfaces in the realization of a new
class of devices for genomic and proteomic applications.
61
Multi-Scale Modeling of the Optical Properties of Triplex DNA
Tahereh Ghane§* , Giorgia Brancolini§ , Daniele Varsano# , and Rosa Di
Felice§
§Center S3, CNR Institute of Nanoscience, Via Campi 213/A, 41125 Modena,
Italy. * Department of Physics, University of Modena and Reggio Emilia, 41125
Modena, Italy. #Department of Physics, University of Rome "La Sapienza",
Piazzale Aldo Moro 5, 00185 Roma, Italy
E-mail: [email protected]
Modified DNAs are appealing because of their biological implications and for possible exploitation
in nanotechnology. In this work we investigate the optical properties of one such modification,
namely triplex DNA.
The optical properties are a powerful tool for the structural and electronic characterization of
nucleic acids with experimental approaches, and it is crucial to have a theoretical counterpart for
understanding and guidance. Our main interest in this work is to reveal the optical fingerprints of
Hoogsteen and Watson-Crick H-bonding in the C+GC triplet in terms
of electronic transitions. We do so by adopting a computational approach based on time-dependent
density-functional theory (TDDFT) 1 . Specifically, we compare the calculated optical absorption
spectra of the C+GC triplet with those of the C+G Hoogsteen pair, the GC Watson-Crick pair and
the single-base components G, C and C+. Furthermore, we wish to address the issue of structural
fluctuations in such calculations. To this aim, we employ a hybrid multi-step methodology in which
the TDDFT calculations are preceded by classical molecular dynamics simulations and data-mining
techniques to determine relevant structures that embody the dynamics at finite temperature.
Our results1 show that: (i) the effect of Hoogsteen H-bonding alone is quite similar to that known
for Watson-Crick H-bonding, namely shifts in the low-energy peaks2; (ii) the simultaneous
presence of Hoogsteen and Watson-Crick hydrogen bonds modifies the spectra of the C+GC triplet
by inducing a peak splitting in the low-energy region; (iii) molecular fluctuations cannot be
neglected in the investigation of the optical properties of nucleic acids; (iv) our cost-effective
approach yields and average optical signal that incorporate the finite-temperature fluctuations.
References.
1 Tahereh Ghane, Giorgia Brancolini, Daniele Varsano, Rosa Di Felice, "The optical properties of
triples DNA from timne-dependent density functional theory", manuscript in preparation.
2 Daniele Varsano, Rosa Di Felice, Miguel A. L. Marques, Angel Rubio, A TDDFT study of
excited states of DNA bases and base assemblies, J. Phys. Chem. B 110, 7129 (2006).
1
www.tddft.org/programs/octopus
62
Structure and electron states of Co-Phthalocyanine interacting with the Cu(111)
surface
J.Fujii1, E.Annese1,2, I. Vobornik1, G. Rossi1,3
1
Laboratorio TASC, IOM-CNR, Area Science Park- Basovizza, 34149 Trieste
2
Università di Modena e Reggio Emilia, via Campi 213/A, 41100 Modena
3
Dipartimento di fisica, Università di Milano, Via Celoria 16, 20133 Milano
We have studied the growth and the electronic properties of Co-Phthalocyanine (CoPc) molecular
layers on Cu(111) with scanning tunneling microscopy (STM) and electron spectroscopy. The
control of organic nanostructures may lead to tuning of the electronic, optical, catalytic and
magnetic properties of interfaces suitable for nano-electronics and sensor applications. Metal
phthalocyanines (MPc) have been widely used in organic devices and sensors as well as dyeing.
MPcs with different metal atoms do have specific behaviour when interfaced with metal substrates
displaying peculiar characteristics that have prompted several studies aiming at understanding the
electronic properties of the MPc single layer or multilayer 1,2.The CoPc molecular film growth on
Cu(111) was monitored by STM and N 1s X-ray absorption spectroscopy (XAS). The combined
STM and XAS results show the flat orientation of the molecule. C 1s, N 1s, core-level
photoemission and Co L 3 edge XAS indicate selective participation of these atoms to the interface
bonds. Angle resolved photoemission, for submonolayer coverage shows that the Cu(111) surface
states undergo a shift to lower binding energies. This binding energy shift and the increase in the
effective mass indicate a charge confinement and redistribution at CoPc/Cu(111) interface. Our
results contribute to the understanding of the interaction process of the molecule with the substrate.
(1) Gargiani, P. Angelucci, M.; Mariani, C.; Betti M. G. Phys. Rev. B 81, 2010, 085412
(2) Baran, J. D et al Phys. Rev. B 81, 2010, 075413.
Corresponding author: Jun Fujii, [email protected]
63
Investigation of resistive switching behavior and nanoscale electronic transport
of Au/Nb-doped SrTiO3 junctions
R. Buzio a, A. Gerbi a, A. Gadaleta a,b, L. Anghinolfi a, F. Bisio a, E. Bellingeri a,
A.S. Siri a,b, D. Marré a,b
a
CNR-SPIN Institute for Superconductivity, Innovative Materials and Devices, C.so Perrone 24,
16152 Genova, Italy
b
Physics Department, University of Genova, Via Dodecaneso 33, 16146 Genova, Italy
Whenever a Schottky barrier is formed at the junction between large work function metals and
electron-doped SrTiO3 (STO) samples, the macroscopic rectifying transport is accompanied by a
resistance switching (RS) behavior. This is likely due to local, field-induced accumulation or
depletion of oxygen vacancies at the vicinity of the metal/STO interface, that in turn might lead to
redox processes responsible for the appearance of resistance switching [1]. Metal/Nb-doped STO
junctions represent a model system for the elucidation of the physical mechanisms driving RS.
Several investigations recently addressed the RS dependence on few intrinsic and extrinsic physical
parameters. There is no doubt that a deeper insight was gained when the macroscale studies were
complemented by the use of local probes, addressing junctions response at the nanoscale [2].
Here we describe the fabrication and electrical characterization of Au/Nb:STO single-crystal
junctions with nanometer thick metal electrodes. We observe an unexpected phenomenon, namely
the coexistence within the same device of highly rectifying properties - under laboratory air - and
bipolar RS - under reducing vacuum conditions. We explore this phenomenology by systematically
studying the junction response under different oxygen and inert gas atmospheres [3].
Since nanometer-scale alterations of the Schottky barrier represent one of the microscopic
mechanisms proposed to explain RS, we report on novel Scanning Tunnelling Microscopy Ballistic Electron Emission Microscopy (STM-BEEM) experiments aimed to directly visualize and
quantify the local inhomogeneities of the effective Schottky barrier height. This approach represents
an original strategy to attempt a correlation with the macroscopic response of the studied system
[4].
[1] R. Waser et al. Adv. Mater. 21, 2632 (2009).
[2] K. Szot et al. Nat. Materials 5, 312 (2006).
[3] R. Buzio, A. Gerbi, A. Gadaleta et al. “Oxygen dependence of carrier transport and resistive-switching in
Au/Nb:SrTiO3 Schottky junctions” in preparation
[4] A. Gerbi, R. Buzio, A. Gadaleta et al. “Hot electron transport in Au/Nb:SrTiO3 structure studied by ballistic electron
emission spectroscopy” in preparation
Andrea Gerbi,
CNR-SPIN Corso Perrone 24, 16152 Genova
e-mail: [email protected]
cell: 3406709619
64
Self-Assembled Monolayer of Cr7Ni Molecular Nanomagnets by Sublimation
A. Ghirri,1,* V. Corradini,1 V. Bellini,1 U. del Pennino,1,3 G. Timco,2 R. Winpenny2
and M. Affronte.1,3
1,*
S3 Centre, Institute Nanoscience - CNR, via G. Campi 213/A , 41125 Modena (I).
School of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
3
Dipartimento di Fisica, Università di Modena e Reggio Emilia, via G. Campi 213/A , 41125
Modena (I).
2
Molecular nanomagnets have attracted a great interest due to the observation of quantum magnetic
phenomena and the possibility, offered by synthetic chemistry, to change the magnetic interactions
almost at will. Antiferromagnetic Cr7Ni rings, in particular, have emerged as suitable candidates for
encoding qubits for quantum information processing applications.
Here we show, by complementary spectroscopic and STM analysis, that Cr7Ni rings are suitable to
be sublimed in UHV conditions. The pristine derivative, Cr7Ni-bu, bonds to gold surface via Van
der Waals interactions, and can diffuse relatively free on it forming monolayers with hexagonal 2D
packing. In a second derivative, Cr7Ni-thiobu, a covalent bond between the molecule and surface
gold adatoms is promoted by adding a functional thiol group to the central dibutylamine counterion. This, in turn, leads to a firm molecular grafting and the formation of a disordered monolayer.
These two examples demonstrate the possibility to control the assembly of large molecular
complex, as rationalized by DFT calculations that establish different energy scales in the deposition
processes [1].
Low temperature XMCD spectra show that the magnetic features of Cr7Ni rings deposited in UHV
on gold remain unchanged with respect to those of the corresponding bulk sample. We also address
the problem of the experimental and theoretical determination of magnetic anisotropy in isolated
molecular spin clusters. The angular dependence of the XMCD spectra at T=8 K and 5 T reveals an
easy-axis anisotropy for the Ni magnetization along the direction perpendicular to the ring whilst
the magnetization of the whole Cr7Ni molecule results preferentially aligned within the ring plane.
These features are well reproduced by theoretical spin Hamiltonian and DFT simulations [2].
Figure 1: STM image of a monolayer of Cr7Ni-bu/Au(111) with, superimposed, the structure
determined by DFT simulations.
References
[1] A. Ghirri, V. Corradini, V. Bellini, R. Biagi, U. del Pennino, V. de Renzi, J. C. Cezar, C. A.
Muryn, G.A. Timco, R.E.P. Winpenny, M. Affronte, ACS NANO, 5, 7090 (2011).
[2] V. Corradini, A. Ghirri, E. Garlatti, R. Biagi, V. De Renzi, U. del Pennino, V. Bellini, S.
Carretta, P. Santini, G. Timco, R. E. P. Winpenny and M. Affronte, Adv. Funct. Mater., in press.
Corresponding author: Dr. Alberto Ghirri, S3 Centre, Institute Nanoscience - CNR, via G. Campi 213/A , 41125
Modena (I). [email protected]
65
Optimizing Picene molecular assembling by Supersonic Molecular Beam
Deposition
S. Gottardia, T. Toccolia, S. Iannottaa, P. Bettottib, A. Cassinesec, M. Barrac, L. Ricciottid, Y.
Kubozonoe
a
IMEM-CNR Divisione di Trento, Via alla Cascata 56/C, I-38123 Povo Trento (Italy)
b
Laboratorio Nanoscienze, Dipartimento di Fisica, Università di Trento, Via Sommarive 14, I38050 Povo Trento (Italy)
c
CNR-SPIN and Department of Physics Science, University of Naples “Federico II”, P.le tecchio
80, 80125, Naples, (Italy)
d
Department of Chemistry, University of Naples ”Federico II”, Via Cinthia, I-80126 Naples, (Italy)
e
Research Laboratory for Surface Science, Okayama University Okayma 700-8530, (Japan)
Picene revealed recently to be a very interesting molecule for organic electronics, since it was
successfully applied to realize the active channels of field-effect transistors able to work even in
ambient conditions or in oxygen atmosphere.[1] Moreover, when intercalated with alkali metals,[2]
picene was demonstrated to exhibit superconductivity at 18K, becoming the first superconducting
hydrocarbon. This discovery renewed the interest in the field of organic superconductors and the
superconductivity was also found in other alkali metals-intercalated molecular-solids based on
polycyclic aromatic hydrocarbons.[2,3].
The possibility to widely tune the electronic properties of these systems is motivating an intense
research activity on these compounds both from theoretical and experimental point of view. So far,
however, very little is known about the self-assembling properties of picene molecules and no
report is yet available to clarify the deposition conditions able to assure the growth of high quality
films. This is a fundamental step to improve the electronic and optoelectronic properties of these
materials making them ready for future device application. Our work goes in this direction. Here we
report an investigation of the growth of picene by supersonic molecular beam deposition on thermal
silicon oxide on silicon and on a self-assembled monolayer of hexamethyldisiloxane (HMDS). The
films morphology show a structure with well separated islands which dimensions and heights
depend on the deposition conditions. At the same time the surface plays a relevant role in the film
growth. In particular on the hydrophobic HMDS the islands are characterized by large regular
crystallites of several microns with an average height of about 50nm, while on bare silicon oxide
the dimension is of about one microns and the average height is of about 74nm; in both cases we
observe very high and sharp island edges. We describe this particular growth as a balancing
mechanism involving the weak interaction between the molecules and the surface and the strong
picene-picene interaction that lead to a different Schwoebel-Ehrlich barrier in the first layer respect
the successive. We study also the charge transport properties of these films by the fabrication of
field-effect transistors devices in top and bottom contact configuration. A maximum mobility value
of 1.2cm2 volt-1 sec-1 is measured in air in case of top contact devices. We compare the results
achieved by supersonic molecular beam deposition with the literature for evaporated picene thin
films
[1]
H. Okamoto, N. Kawasaki, Y. Kaji, Y. Kubozono, A. Fujiwara, M. Yamaji, J. Am. Chem.
Soc. 2008, 130, 10470.
[2]
R. Mitsuhashi, Y. Suzuki, Y. Yamanari, H. Mitamura, T. Kambe, N. Ikeda, H. Okamoto, A.
Fujiwara, M. Yamaji, N. Kawasaki, Y. Maniwa, Y. Kubozono, Nature 2010, 464, 76.
[3]
Y. Kubozono, H. Mitamura, X. Lee, X. He, Y. Yamanari, Y. Takahashi, Y. Suzuki, Y. Kaji,
R. Eguchi, K. Akaike, T. Kambe, H. Okamoto, A. Fujiwara, T. Kato, T. Kosugi, H. Aoki, Phys.
Chem. Chem. Phys. 2011, 13, 16476.
Corresponding author: Stefano Gottardi, email: [email protected],
66
Crystal Phase Dependent Photoluminescence of 6,13-Pentacenequinone
P. De Marco1,2, S. Lettieri3,4*, A. Ambrosio3,4, F. Bisti1, F. Fioriti1, P. Maddalena3,4, M.
Passacantando1, S. Prezioso1, S. Santucci1 and L. Ottaviano1,2
1 Dipartimento di Fisica, Università dell'Aquila, Via Vetoio 10, 67100 L'Aquila (Italy)
2 SPIN-CNR, UOS L'Aquila, Via Vetoio 10, 67100 L'Aquila, Italy
3 SPIN-CNR, UOS Napoli, Via Cintia 80126 Napoli (Italy)
4 Dipartimento di Scienze Fisiche, Università di Napoli "Federico II", Via Cintia, 80126 Napoli, (Italy)
--
6,13-Pentacenequinone (PQ, C22H12O2) is an organic molecule belonging to the family of linear
para-quinones and has been mainly studied as dominant chemical impurity of commercially
available pentacene, being a product of its oxidation. As molecule, PQ is a strong light emitter
exhibiting an intense photoluminescence (PL) spectrum peaked in green and yellow range (593 and
630 nm). As molecular solid, investigations on its morphology and crystal structure demonstrated
that PQ molecules assemble in two crystal phases referred to as ”bulk” and ”thin-film” both with a
P21/c monoclinic symmetry but having different values for the elementary cell parameters. It has
been recently demonstrated [1] that during growth onto SiO2 the PQ crystal packing undergoes a
transition from “bulk” phase (2D dendritic layer at initial stage of growth) to formation of
rectangular-shaped crystals in the “thin-film” phase beyond a critical thickness of about 3.6 nm.
In a preliminary study on its PL emission, it was claimed that photoluminescence spectra of PQ
crystals were essentially independent on crystalline packing [2], a strong statement that was found
to be somehow inconsistent with subsequent results [3,4].
In this contribution it is evidenced how indeed the differences in the two type of PQ molecular
packing strongly influence the PL spectral response. Such statement results from systematic
thickness dependent investigation through static and time-resolved photoluminescence
spectroscopy analysis, combined with SEM and XRD analysis.
Photoluminescence properties of PQ films (growth onto SiO2) of 5 and 30 nm thickness were
studied, showing a multiplet structure that can be ultimately assigned to the superposition of the
emission spectra from two different crystal phases, namely the above mentioned ”bulk” and the
”thin film” phase, emitting respectively in the 500-600 nm and 600-750 nm spectral ranges. These
assignments, supported by parallel SEM and XRD investigations, are discussed in the light of other
PL analysis of PQ reported in literature. The blue shift of the "bulk” phase PL spectrum is assigned
to its smaller (about 9% less than in “thin film” phase) molecular packing density in the ab-plane,
and accordingly, to a decreased π−π orbital overlap.
[1] P. De Marco, F. Fioriti, F. Bisti, P. Parisse, S. Santucci, and L. Ottaviano, J. Appl. Phys. 109, 063508 (2011)
[2] D. K. Hwang, K. Kim, J. H. Kim, S. Ima, D. Y. Jung, and E. Kim, Appl. Phys. Lett. 85, 5568 (2004)
[3] H. J. Nam, Y. J. Kim, and D. Y. Jung, Bull. Korean Chem. Soc. 31, 2413 (2010)
[4] P. Parisse, D. Luciani, S. Santucci, P. Zuppella, P. Tucceri, A. Reale, and L. Ottaviano, J. Phys. D: Appl. Phys. 41,
112003 (2008)
*
Presenting author. E-mail: [email protected]
67
Comparison of ageing for different encapsulated OLEDs on glass substrates.
P. Tassini, M. G. Maglione, A. Bonucci*, A. De Girolamo Del Mauro, G. Nenna, G. Nobile,
T. Fasolino, G. Pandolfi, and C. Minarini
EEA C. R. Portici; UTTP-AO; P.le E. Fermi, 1; Località Granatello, 80055 Portici (A) Italy
*
SAES Getters S.p.A., Application Engineering and System Analysis department Research &
Innovations; Viale Italia,77; 20020 Lainate (MI) Italy
Starting with primeval work of C.W. Tang and S.A Van Slyke on OLEDs in 1987 [1], these devices
have attracted an increasing attention from research and industries for displays and lighting
applications. But, OLEDs performances degrade if exposed to atmosphere, because moisture and
Oxygen react with materials of the devices very quickly. Protection offered by encapsulation and
sealing only is not sufficient to maintain OLEDs, so it is necessary to insert a desiccant (or getter) in
the architecture of the devices [2] to capture the moisture. Without high performances sealants and
getters, the lifetime of devices is very limited and they could not be proposed for any practical
application.
When glass substrates are used, the permeability of the edge sealant is critical. Without getters, the
ingress of water and Oxygen into the encapsulated volume must be kept below about 10-9 g/day and
10-8 cm3/atm/day, respectively. To achieve these levels, not only the bulk permeability but also the
control of the adhesion of the sealant to the glass seems to be an important factor of the sealing
material. So, desiccants are essential to improve the tolerance for this influx, as well as to soak up
water or oxygen that desorb from the materials inside the device after sealing.
Encapsulated OLEDs have been prepared on glass with a getter inside the enclosed volume.
Electrical and optical performances of the devices have been measured along the time, to evaluate
their lifetime and compare the influence of different materials in the devices’ stack.
In particular, different types of OLEDs have been fabricated, with PEDOT:PSS, PANI and CuPc as
hole injection layer (HIL); the structure is: glass / ITO / HIL / NPD / Alq3 / LiF / Al.
Devices have been encapsulated immediately after fabrication with a glass lid, sealed using the
same epoxy resin as sealant and a getter as desiccants: both these materials are from SAES.
Some of these devices have also been aged for 200 hours in accelerated lifetime conditions,
showing negligible variation of light emission, confirming the efficacy of using encapsulation and
getter in preserving the OLED.
References.
[1] C.W. Tang, S.A. VanSlyke, Appl. Phys. Lett., 51 (1987).
[2] P.E. Burrows, V. Bulovic, S.R. Forrest, L.S. Sapochack, D.M. McCarty, M.E. Thompson,
Appl. Phys. Lett., 65 (1994), p. 2922.
Corresponding author:
Maria Grazia Maglione
ENEA - C.R. Portici
Laboratorio Nanomateriali e Dispositivi (UTTP-NANO)
Piazzale Enrico Fermi, 1
80055 Portici (NA), Italy
tel.: +39 081 7723249
e-mail: [email protected]
68
Dye Sensitization of Zinc Oxide with Zinc Phthalocyanines: from Isolated
Molecules to Nanostructured Molecular Aggregates
Giuseppe Mattioli,1 Claudio Melis,2 Giuliano Malloci,2 Francesco Filippone,1 Paola Alippi,1
Paolo Giannozzi,3 Alessandro Mattoni,2 and Aldo Amore Bonapasta.1
1
Istituto di Struttura della Materia del CNR, v. Salaria Km 29,300 - C.P. 10 I-00016 Monterotondo Stazione (RM) Italy,
2
Istituto Officina dei Materiali del CNR UOS-SLACS, Cittadella Universitaria, I-09042
Monserrato (Ca), Italy,
3
Department of Chemistry, Physics, and Environment, University of Udine, via delle Scienze 208,
33100 Udine, Italy, and DEMOCRITOS IOM-CNR National Simulation Center, 34014 Trieste, Italy
Hybrid photovoltaic (HPV) cells employing organic and inorganic components for light
harvesting and energy production have received enormous research attention. in the last years.[1]
However, some drawbacks for their large-scale application, as a low efficiency and a short
durability, claim for a deepen knowledge of the processes at the core of their functioning. Such
processes are closely related to the properties of the interface formed by the organic (electron
donor) light absorber and the inorganic (electron acceptor ) substrate.
In this context, we have investigated the properties of the hybrid, donor-acceptor interface
formed by zinc phthalocyanine (ZnPc) molecules and the zinc oxide (ZnO) semiconductor by using
a combination of ab initio DFT and TDDFT [2] and model potential [3] theoretical methods. The
attention is focused on the effects of molecular assembling on the hybrid interface by considering
the evolution of the ZnPc-ZnO electronic and optical properties from isolated molecules to
nanostructured molecular aggregates.
As major results, we find that:
(I) ZnPc molecules and their aggregates in contact with the ZnO surface are characterized by a
strong molecule-surface coupling leading to the appearance of novel, strategically located,
electronic levels which can significantly favor the ignition of photogenerated electrons from the
molecule to the substrate.
(ii) in the case of planar nanostripes (referred to as J-type aggregates), inter-molecular interactions
induce a red shift of the ZnPc absorption lines. This result gives a firm theoretical support to the
experimentally observed relationships between such a red shift and the formation of J-type
aggregates as well as to the potential, beneficial effect of molecular aggregation on the light
harvesting properties of the ZnPc/ZnO systems.
All in all, present results indicate that structural, electronic and optical properties can be
achieved in ZnO surfaces sensitized by ZnPc molecules of high interest for improving the
efficiency of different hybrid photovoltaic devices like, e. g., dye-sensitized or bulk-heterojunction
solar cells.
[1] Grätzel, M. Recent Advances in Sensitized Mesoscopic Solar Cells. Acc. Chem. Res. 2009, 42,
1788.
[2] Giannozzi, P. et al., QUANTUM ESPRESSO: J. Phys.: Condens. Matter 2009, 21, 395502.
[3] Melis, C.; Raiteri, P.; Colombo, L.; Mattoni, A. Self-assembling of Zinc Phthalocyanines on
ZnO (10-10) Surface through Multiple Time Scales. ACS Nano 2011, 5, 9639.
Corresponding author: Giuseppe MATTIOLI, Istituto di Struttura della Materia del CNR, v. Salaria
Km 29,300 - C.P. 10 I-00016 - Monterotondo Stazione (RM) Italy, phone 0690672836,
[email protected]
69
ITO-free white organic light emitting diodes based on multi-cavity technology
and PIN technology
1
M. Mazzeo1,2, F. Mariano1, A. Genco1, S. Carallo2, G. Gigli1,2
Dipartimento Ingegneria dell’ Innovazione, Università del Salento, Via Arnesano, Lecce, 73100,
Italy,
2
NNL Istituto Nanoscienze- CNR Via Arnesano 16, Lecce, 73100, Italy
[email protected]
White Organic light-emitting diodes (WOLEDs) are promising light sources which could offer an
important progress in indoor lighting, where luminous efficacy (LE) higher than 60 lm/W and color
rendering index (CRI) larger than 80 are needed. Indeed using different organic stack and photonic
layouts, LE larger than 30 lm/W, CRI near the limit of 100 and possibility to use lightweight
flexible plastic substrates have been separately demonstrated by this class of optoelectronic devices.
Nevertheless the simultaneous achievement of all these targets is still a big challenge. A promising
architecture to increase the Luminous efficacy and simultaneously avoid the use of ITO is based on
the organic/metallic microcavity resonators. However, this technology so far has given
unsatisfactory results because of interface problems between low work function metals and deep
energy level of hole transporting organic layers. In addition high selective properties of cavities is
not compatible with white emission. Here we propose an innovative photonic architecture, named
coupled-microcavity white OLED (CM-WOLED), where two or more cavities are coupled through
thin high reflective metal layers, resulting in the generation of two or more electromagnetic modes
sustained by the whole cavity [1]. By electrically doping the transport layers with electron acceptors
molecules we are able to remove ITO layer, to couple hole transport layers with high work function
metal and to achieve white emission as well. With our approach, the color emission, the outcoupling efficiency, and the CRI can be simultaneously optimized in the same cavity structure. This
opens new pathways to fabricate a novel class of very cheap, high color quality, and ITO-free
devices for the next generation of “plastic-light” sources. In particular using two complementary
color fluorescent materials white color electroluminescence with CRI of 84 and LE of 15lm/W have
been achieved in double cavity configuration. Using Red, Green, and Blue phosphorescent
materials we have exploited three-coupled cavities to achieve an efficiency of 85 and LE of 34
lm/W and 14lm/W (15Cd/A), respectively on rigid glass substrates and flexible plastic (PET) ones.
To our knowledge these results are the best performances so far reported for ITO-free OLEDs and
in absolute the highest values for flexible WOLEDs. . The approach is based on an ITO-free
technology, thus allowing for low cost devices and a really breakthrough towards cheap highly
efficient, high color quality indoor lighting.
[1] Mazzeo, M., et al. Shaping White Light Through Electroluminescent Fully Organic Coupled
Microcavities, Adv. Mater. Vol 22, 4696-4700, 2010.
70
Soft X-ray reflectivity studies of 1,4 Benzenedimethanethiol ultrathin films on
Au at the C K-edge
S. Mukherjee1*, L. Pasquali2,3, F. Terzi4, A. Giglia2, N. Mahne2, V. Esaulov5, M. Canepa6, S.
Nannarone2,3
1
Abdus Salam International Centre for Theoretical Physics, Trieste, Italy
2
IOM-CNR Lab TASC, Basovizza, Trieste, Italy
3
Dipartimento di Ingegneria dei Materiali e dell'Ambiente, Universita' di Modena e Reggio Emilia,
Modena, Italy
4
Dipartimento di Chimica, Universita' di Modena e Reggio Emilia, Modena, Italy
5
Institut de Sciences Moléculaires d'Orsay, Université Paris Sud, Orsay, France
6
Dipartimento di Fisica, Università di Genova, Genova, Italy
Dithiol molecules, in particular, molecules containing aromatic rings, have been the object of much
investigation because of potential use in, for example, molecular electronics thanks to their
conducting properties and the possibility to graft the thiol ends to two metal electrodes. Extended
studies of formation of 1,4 benzenedimethanethiols (BDMT) SAMs on gold substrates exploiting
both in vacuum and in-liquid deposition methods have been carried out. Here we present and
discuss the application of resonant specular soft-X-ray reflectivity technique to study the adsorption
geometry and electronic properties of BDMT monolayer on Au. Resonant reflectivity is an
appropriate technique for studies of systems under applied fields (either magnetic or electric) or in
the presence of controlled environment different from ultra-high vacuum, accessing buried
interfaces as well as to avoid sample-charging effects. Reflectivity spectra at the C K-edge were
taken at BEAR beamline (http://www.elettra.trieste.it/experiments/beamlines/bear/index.html) with
linearly polarized light with different directions of polarization. Dichroism effects were clearly
observed. Experimental evidences have been rationalized by simulating reflectivity using the
indigenous code OPAL (Optical Properties of Anisotropic Layers) that simulates the wave
propagation in anisotropic layered media described by anisotropic dielectric tensor. The dielectric
tensor of the BDMT film was modeled allowing different chemisorption geometries through
rotations about sample axes and calculating the elements of the tensor starting from oscillator
strengths of polarization dependent optical transitions at the C K-edge obtained using a commercial
density functional theory code (StoBe). Comparison of experiment and simulations reveal a tilted
configuration of the molecules on the Au substrate. The above results allow a more quantitative
understanding of the electronic properties of the adsorbed BDMT monolayer. Moreover the
approach is a contribution towards applicability of the soft X-ray reflectivity technique in the
understanding of adsorption geometries of ultrathin films of soft matter.
Corresponding author: Subhrangsu Mukherjee, Abdus Salam International Centre for Theoretical Physics, Strada
Costiera 11, 34151, Trieste, Italy. Email: [email protected]
71
Manipulation and spectroscopy of single phthalocyanine molecules on
InAs(111)A with a low-temperature scanning tunneling microscope
Christophe Nacci1, Kiyoshi Kanisawa2 and Stefan Fölsch1
Paul-Drude-Institut für Festkörperelektronik, Berlin, Germany
2
NTT Basic Research Laboratories, NTT Corporation, Atsugi, Japan
1
Phthalocyanine is a promising class of organic molecules to develop functionality concepts based
on a hybrid molecule-semiconductor scheme.
We report a low-temperature scanning tunneling microscopy (STM) study of individual
naphthalocyanine (NPc) and tin phthalocyanine (SnPc) molecules adsorbed on the InAs(111)A
surface. InAs(111)A is In-terminated and free of partially filled dangling bonds due to its (2×2) Invacancy reconstruction [1].
STM imaging of the frontier molecular orbitals suggests that NPc is physisorbed. The molecular
orbitals are left unperturbed to a large extent upon adsorption, indicating a weak electronic coupling
to the semiconductor template.
The non-planar SnPc adsorbs in two different configurations with the central Sn atom either above
or below the molecular plane (SnPc(up) and SnPc(down)). Reversible switching between the two
conformers has been achieved by means of STM tip-induced excitation [2]. Our experimental
findings reveal that SnPc(down) is characterized by a stronger surface bonding compared to
SnPc(up). This enables to reposition the SnPc(up) molecule by STM-based lateral manipulation,
whereas this is not possible for SnPc(down).
The reversible switching can thus be utilized to either move the molecule or to anchor it to the
surface.
We acknowledge support by the Deutsche Forschungsgemeinschaft (SFB658).
[1] A. Taguchi and K. Kanisawa Appl. Surf. Sci. 252 (2006) 5263
[2] Ch. Nacci, K. Kanisawa, and S. Fölsch, J. Phys. Cond. Matter (accepted)
72
The BEAR beamline at Elettra in the VIS-Soft X-ray region – a tool to
investigate ultra-thin organic films
A,Giglia1, F.Frassetto2, S.Mukherjee3, L.Pasquali1,4, L.Poletto2 and S.Nannarone1,4*
1
IOM-CNR Lab TASC, Basovizza, Trieste, Italy
LUXOR-Institute of Photonics and Nanotechnologies-National Council for Research, Padova,
Italy
3
Abdus Salam International Centre for Theoretical Physics, Trieste, Italy
4
Dipartimento di Ingegneria dei Materiali e dell'Ambiente, Universita' di Modena e Reggio Emilia,
Modena, Italy
2
BEAR beamline at Elettra (http://www.elettra.trieste.it/experiments/beamlines/bear/index.html )
provides photon-in-photon-out investigation tools flanked by electronic spectroscopies with
emphasis on anisotropic low dimensional and layered materials addressing to interplay among
electronic properties (including magnetism), local structure and morphology. BEAR provides UHV
sample environment with in-situ preparation of ultra-thin films and sample and substrate treatments
including annealing , electron and ion bombardment and magnetization (pulsed excitation) in
remanence. Sample temperature in measuring condition ranges from 120 K to 500 K. Light spot
features - on the 2.7-1600 eV energy range - 30x100 m2 spot size (typical), 20x20 (h x v) mrad2
divergence, 3000 (peak 5000) energy resolution, variable (calibrated attenuators) flux 1011 ph/s at
100 eV (peak) and selectable polarization from near linear to right/left elliptical. The experimental
chamber hosts photodiodes, channeltrons, electron analyzer, fluorescence detector (from B K to Mg
K edges) and spectral (Vis-UV) luminescence detector. Incidence and collection geometries are
highly flexible. Light incidence continuously varies from s to p, photon detectors cover the 2 solid
angle and the angle of incidence varies between 0 and 90°. Available spectroscopies include
specular (dichroic) and diffuse reflectivity, (dichroic) absorption (TEY, AEY and Vis-Soft-X
photon yield), fluorescence, luminescence (spectral), photoemission and Auger. Available data
analysis include reflectivity and absorption spectra in anisotropic layered media (see also
S.Mukherjee et al.) and EXAFS/NEXAFS analysis using DFT simulation of optical transitions and
geometry optimization. Activities involving organic materials carried out, both by users groups on
public beamtime and in in-house research dedicated beamtime, primarily at the K edges of light
elements (C, N, O) as well as Vis-UV wavelengths deal with organic electronic materials, organic
semiconductor-metal interfaces, liquid crystal polymers, Langmuir-Blodgett films, organicinorganic nanocomposites and biomaterials. A gallery of the obtained results will be presented.
Beamline can be accessed through proposals for public beamtime (On-line submission using the
Virtual Users Office at the following URL: https://vuo.elettra.trieste.it/), collaboration with
beamline scientists and through commercial agreements (offers must be placed to CNR – IOM,
Trieste).
Corresponding author: Stefano Nannarone, IOM-CNR, S.S. 14 Km 163.5, 34149 Trieste, Italy.
Email: [email protected]
73
Electronic properties of tetraphenylporphyrins: the role of fluorine
M. Nardi*, R. Verucchi, L. Aversa, S. Iannotta
Istituto dei Materiali per l’Elettronica ed il Magnetismo, IMEM–CNR, Via alla Cascata 56/C –
Povo, 38123 Trento, Italy
*Institut fur Physik, Humboldt-Univ. zu Berlin, Newtonstrasse 15, 12489 Berlin, Germany
M. Casarin, A. Vittadini
Dip. di Scienze Chimiche, Univ. degli Studi di Padova, Via Marzolo 1, 35131 Padova, Italy and
Istituto di Scienze e Tecnologie Molecolari ISTM-CNR, Via Marzolo 1, 35131 Padova, Italy
Stefano Nannarone
Dip. di Ingegneria dei Materiali e dell’Ambiente, Univ. degli Studi di Modena e Reggio Emilia,
Strada Vignolese, 905 - 41125 Modena
π-conjugated organic molecules have been often used as semiconducting materials in thin film
devices by exploiting their p-type carrier transport. Among them, porphyrins and related derivatives
have attracted a great deal of interest as a consequence of their electronic and optical properties
which can be additionally tuned and enhanced through molecular engineering. The switch of
electronic transport properties from p- to n-type through the substitution of hydrogen termination
with halogen species such as fluorine is an intriguing opportunity, pushing research activity towards
the synthesis of organic systems showing both electron acceptor and donor characteristics. As a
matter of fact, the possibility of achieving electron based transport properties, typical of inorganics,
could pave the way for the creation of a p-n junction fully based on organic materials.
In this contribution, the results of a combined experimental and theoretical study of the electronic
properties of tetrakis(pentafluorophenyl)porphyrin in the native (C44H30N4, H2TPP) and partially
fluorinated (C44H10F20N4, H2TPP(F)) are presented and discussed. A non conventional synthetic
method, based on the use of supersonic molecular beams seeded by the organic precursor, is the so
called Supersonic Molecular Beam Deposition (SuMBD) technique. Thin films have been deposited
and analyzed in-situ at the BEAR beamline, ELETTRA synchrotron radiation facility (Trieste,
Italy). Surface photoelectron spectroscopy (PES) experiments have been performed to investigate
both the valence band and the core levels of organic thin films. X-ray absorption (XAS) analysis at
the several K edges will be shown. Density Functional Theory (DFT) calculations carried out for
the isolated molecule results to be fundamental in identifying the role of each chemical species,
leading to a reliable interpretation of PES and XAS spectra. Resonant photoemission valence band
spectroscopy has been performed at the several elemental K absorption edges in order to emphasize
the different contribution of the several chemical species and groups in the molecules. XAS analysis
at different photon beam incidence geometries will be shown, in order to study the structural
rearrangement of molecules in thin film. We believe the comparison between H2TPP and
H2TPP(F) electronic properties will a step towards the design of fully organic p-n junctions by
using these macrocycles.
Corresponding author: Marco Nardi, Institut fur Physik, Humboldt-Univ. zu Berlin, Newtonstrasse 15, 12489 Berlin,
Germany, email: [email protected]
74
Stochastic dynamics for a single vibrational mode in molecular Junctions
*1
A. Nocera*1, C.A. Perroni2, V. Marigliano Ramaglia2 and V. Cataudella2
Dipartimento di Fisica E. Amaldi, Università di Roma Tre, Via della Vasca Navale 84,
I-00146 Roma, Italy
2
CNR-SPIN and Università degli Studi di Napoli Federico II
Complesso Universitario Monte Sant’Angelo, Via Cintia, I-80126 Napoli, Italy.
We propose a very accurate computational scheme for the dynamics of a classical oscillator coupled
to a molecular junction driven by a finite bias, including the finite mass effect. We focus on a
minimal model for the molecular junction: the Anderson-Holstein model. As concerns the oscillator
dynamics, we are able to recover a Langevin equation confirming what found by other authors with
different approaches and assessing that quantum effects come from the electronic subsystem only.
Solving numerically the stochastic equation, we study the position and velocity distribution
probabilities of the oscillator and the electronic transport properties at arbitrary values of electronoscillator interaction, gate and bias voltages. The range of validity of the adiabatic approximation is
established in a systematic way by analyzing the behavior of the kinetic energy of the oscillator.
Due to the dynamical fluctuations, at intermediate bias voltages, the velocity distributions deviate
from a gaussian shape and the average kinetic energy shows a non monotonic behavior. In this same
regime of parameters, the dynamical effects favor the conduction far from electronic resonances
where small currents are observed in the infinite mass approximation. Finally, we show that our
model is able to reproduce all the main features observed in recent transport experiments through
suspended carbon nanotubes driven by an external antenna.
75
Investigation of 4HCB molecule by synchrotron based techniques and
theoretical DFT methods
Giorgia Olivieri a, *, Albano Cossaro a, Alessandro Fraleoni Morgera b
a
CNR-IOM, Laboratorio TASC, Basovizza, SS14, Km 163.5, 34012 Trieste, Italy
b
Sincrotrone Trieste SCpA - SS 14, km 163.5, 34149 Basovizza (TS), Italy
Organic semiconducting molecules have gained a lot of attention because of their promising
application in organic electronics. Despite the large number of prototype organic electronic devices
still a lot of effort is needed to understand the main electronic transport properties of the active
organic semicondutor governing the devices operation. In this view, organic semiconducting single
crystals (OSSCs) represent one of the model materials to pursue this goal because of their high
purity, absence of defects and long range structural order.
Recently reported OSSCs based on the dipolar 4-hydroxycyanobenzene (4HCB) molecule (Fig.1)
were shown to have reproducible 3D anisotropic transport properties along the three
crystallographic axes [1-3]. This strong evidence has motivated our synchrotron based
spectroscopic study of the 4HCB molecule. In fact to deeply understand the origin of the observed
electrical properties, we need a picture of the molecular energy levels and how they are modified
when the free molecule is embedded in the crystal and/or interacts with other materials such as
metals.
In order to study both the occupied and unoccupied molecular levels, we performed both
photoemission and X-ray absorption spectroscopy measurements. We started with the total
characterization of the molecule in the gas phase by means of X-ray Photoemission Spectroscopy
(XPS) from core and valence levels and Near Edge X-ray Absorption Fine Structure Spectroscopy
(NEXAFS) across the three peculiar 4HCB edges, namely carbon, nitrogen and oxygen. We
measured also the Resonant Photoemission Spectroscopy (RPES) in order to assign the different
molecular valence levels to the different atoms of the molecules. We used then density functional
theory (DFT) to interpret the spectra, calculating molecular properties such as density of states,
occupied and unoccupied molecular orbitals and XPS chemical shift. The result have been then
used as reference to evaluate the properties of the molecule in its solid state phase. We evaporated
in Ultra High Vacuum a thick film of 4HCB on a gold substrate. Both XPS, NEXAFS and RPES
spectra have been taken and compared with the gas phase data. The NEXAFS shows a preferential
orientation in the molecular growth geometry, indicating the possible aggregation of the molecules
in their crystalline form. Moreover, a stronger quenching of the RPES resonances is observed on the
nitrogen edge with respect to the carbon one, suggesting that the cyano group could be directly
involved in the electronic transport of the OSSC.
Fig 1: Chemical structure of
4-hydroxycyanobenzene
(4HCB)
* Corresponding author: Tel. +39 0403758065; E-mail adress: [email protected]
[1] B. Fraboni, A. Fraleoni-Morgera, A. Cavallini, Organic Electronics 11 (2010) 10–15
[2] B. Fraboni, C. Femoni, I. Mencarelli, L. Setti, R. Di Pietro, A. Cavallini, A. Fraleoni-Morgera, Adv. Mater. 2009,
21, 1835–1839
[3] B. Fraboni, R. DiPietro, A. Castaldini, A. Cavallini, A. Fraleoni-Morgera, L. Setti, I. Mencarelli, C. Femoni, Organic Electronics 9 (2008) 974–978
76
Electronic Properties of Metal Octaethylporphyrins ordered layers mediated by
Au(111) substrates
Maddalena Pedio1, Manvendra Kumar1, Arrigo Calzolari2, R. Felici3, A. Resta3
1
CNR-IOM, TASC, Area Science Park, Basovizza, Trieste, Italy
2
CNR-NANO Modena, Italy
3
ESRF, Grenoble, France
One of the main challenges of artificial molecular electronics is the controlled growth molecular
layers on the nanometer scale. Organic molecule deposition on surfaces has opened a new
extremely promising field towards new materials that exploit the functionalization of organic layers
obtained by a controlled growth [ref]. One of the key issues in this field is to single out their
driving interaction forces with other materials. In this context the porphyne-derived aggregates
attracts an intense research activity.
The structural and electronic properties of NiOEP self assembly layers deposited onto the Au(111)
23x√3 surface have been characterized combining S-XRD and LEED measurements with the data
obtained by photoemission (PES) /inverse photoemission (IPS) techniques and DFT theoretical
calculations.
Two different ordered phases of NiOEP on Au(111) have been found for coverages up to 1 ML,
with matrices 03 −51 (str. I) and −54 50 (str. II). This polymorphism is due to differences in the




intermolecular orientations and in-plane density. Both structures are characterized by the external
ethyl groups pointing in the same upward direction and differs to the bulk NiOEP structures
(triclinic and tetragonal). No structural perturbation takes place on the substrate Au(111)
herringbone.
The differences in the two in-plane molecular arrangements are reflected in the frontier orbitals
perturbation with respect to the isolated molecules and interpreted by means of Density Functional
theory. The two structures I and II are characterized by specific b1g (Ni 3d) and 2eg
(organometallic orbital) energy positions. Our DFT simulation support the PES/IPS experimental
finding of structure I (low density): a perturbation of the molecular orbitals is induced by the
upward rotation of the ethyl groups and the molecular electrostatic dipole results increased of a
factor 3.
We interpreted the changes in the b1g-2eg (LUMO-LUMO+1) region as due to the variations of the
intermolecular interactions AND of the back-donation and effective charge at the Ni central atom of
porphine macrocycle, induced by the specific in-palne packing of the two structures. In structure I a
weakening of the π bonding is induced by the ethyl upward and the dipoles at interfaces. In case of
structure II the Ni-N result more strongly bonded with respect to isolated NiOEP or molecular
multilayer. The possible framework should consist in a compression of the NiOEP molecule
followed by a shorter Ni-N bond and a donor charge transferred between Ni and Au substrate.
The electrostatic NiOEP dipole and the tail effects induced in the underneath gold substrate well
explain the experimental variation of the work function.
Corresponding author: Maddalena Pedio, CNR-IOM, TASC Area Science Park, S.S.14, Km 163.5
34149, Basovizza, Trieste, Italy
e-mail: [email protected]
77
Electronic properties of Transition-Metals Porphyrins
Andrea Goldoni1, Giovanni Di Santo1, Carla Castellarin-Cudia1, Patrizia Borghetti1, Arrigo
Calzolari2, Paolo Umari3, Manvendra Kumar4, Maddalena Pedio4
1
Sincrotrone Trieste, in Area Science Park, Basovizza, (Trieste) 34149 Italy
2
CNR-NANO Modena, Italy
3
Universita’ di Padova
4
CNR-IOM, TASC Area Science Park Buil. MM, S.S. 14, Km 163.5, 34149 Basovizza, Trieste, Italy
Transition metals porphyrin complexes have attracted much interest in the last few years. They play
a major role in biological processes (photosynthesis, oxygen binding) and are used for dye-sensitive
photovoltaic devices and organic light emitting diodes. Moreover organic molecule deposition on
surfaces has opened a new extremely promising field towards new materials that exploit the
functionalization of organic layers obtained by a controlled growth [ref]. One of the key issues in
this field is to single out their driving interaction forces with other materials.
To these purposes, the up-to-date knowledge of the electronic properties of single porphyrin
molecules is demanding.
Discrepancies are found in the literature on the energy level assignments, and in particular the
spectroscopic features of the highest occupied Molecular Orbital (HOMO) and Lowest Unoccupied
Molecular Orbital are still unclear.
We present a systematic characterization of the electronic properties of tetraphenyl and octaethyl
porphyrins, obtained by C and N K edges absorption and electron spectroscopies in the gas-phase
and in multilayer pristine thin films.
We found that the energy levels of the filled and empty molecular orbitals show differences related
to the central atom nature and to the molecular groups external to the macrocycle ring.
For example in the tetraphenyl series the addition to the metal free H2TPP of the Zn central atom,
with its completed d band, induces a rigid shift in the filled orbitals and a slight perturbation of C
K- edge, while much stronger differences are detected in case of octaethyl metal free and ZnOEP.
The N1s and C1s present energy shifts due to the variation of the charge induced by the metal
central atom and the perturbation on the conjugation induced by the external group. The central
metal atom induces a shift of the first unoccupied π* orbital. The comparison between Gas phase
Valence Band, C and N K-edges NEXAFS with Inverse Photoemission spectra allow to quantify
the energy level alignment and the sequence of the metal and metallorganic electronic states.
These trends can be rationalized by means of our DFT calculations. In particular we investigated the
effect of the molecular structure and composition on the molecular electrostatic dipole that can have
important effects in organic-inorganic interfaces and in Self Assembled Monolayer structures.
The combination of NEXAFS, Photoemission and Inverse Photoemission with DFT calculation
enlightens the role played by the central atom and the external groups in the porphyrines.
Corresponding author: Maddalena Pedio
CNR-IOM, TASC Area Science Park Building MM
S.S. 14, Km 163.5, 34149 Basovizza, Trieste, Italy
[email protected]
78
TCPP anchoring process on porous nano-crystalline TiO2 layers deposited by
sputtering at ~150°C on transparent ZnO:Al substrates: effects of annealing the
substrate (500°C) before the sensitization.
Giovanna Pellegrino1, Guglielmo Guido Condorelli2 and Alessandra Alberti1*
1
2
IMM-CNR, Zona Industriale, VIII Strada 5, 95121, Catania, Italy
Università degli Studi di Catania and INSTM UdR di Catania, Viale Andrea Doria, 6-95125
Catania, Italy
A free-base porphyrin bearing four carboxylic groups, the 5,10,15,20-tetrakis(4carboxyphenyl)porphyrin (TCPP), has been used as light-harvester for the sensitisation of semiconductive TiO2/ conductive (11-20) oriented ZnO:Al (AZO) bi-layers to be applied as photo-anode
in DSSC. The nano-structured TiO2 thin layer, obtained by DC Reactive Sputtering, consists mostly
of nano-crystalline anatase grains with a small amount of rutile domains formed in spite of the very
low temperature used during the deposition process (~150°C). The layer is continuous and porous.
The TCPP-sensitization was performed both on the as
deposited TiO2/AZO bi-layer and also on the bi-layer after
TiO2
a thermal treatment at 500 °C, thus reproducing the more
conventional condition for the sintering of the TiO2 pastes.
As demonstrated by X-Ray Diffraction and X-ray
Reflectivity, the thermal treatment determines a structural
re-arrangement of the TiO2 domains structure accomplished
by an increase of the grains size probably due to a ripening
process. Beside the significant structural modification, a
difference in the binding geometry of the TCPP anchored
on the two TiO2 surfaces (in terms of number of reacted
TCPP
COOH groups) has been found. High Resolution X-ray
Photoelectron Spectroscopy has revealed that the TCPP
takes in both cases a standing configuration (thus achieving
a very high molecular density: d~3x1013 molecules/cm2), with anchoring via a single-site tethering
being more probable on the annealed sample with respect on the as deposited layer. The difference
in the binding arrangement and, thus, in the number of the interacting COO- functionalities could be
ascribed to the different morphology of the two TiO2 surfaces (as shown by Transmission Electron
Microscopy plan view) and could affect the efficiency of the carrier transfer from the TCPP to the
nano-sized TiO2 layer.
Corresponding author:
Alessandra Alberti
CNR-IMM
Stradale Primosole 50, 95121 Catania, Italy
Tel: ++39 095 5968214
[email protected]
79
Light-emitting polymer nanofibers: next-generation organic semiconductor
nanostructures for nanoelectronics and nanophotonics
Luana Persano1,2, Andrea Camposeo1,2 and Dario Pisignano1,2,3
1
National Nanotechnology Laboratory of Istituto Nanoscienze-CNR, , Università del Salento, via
Arnesano, I-73100 Lecce, Italy
2
Center for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia, via Barsanti,
I-73010 Arnesano, Italy
3
Dipartimento di Matematica e Fisica “Ennio De Giorgi”, Università del Salento, via Arnesano, I73100 Lecce, Italy
Polymeric nanofibers made by conjugated polymers and other light-emitting organic
molecules are attracting an increasing interest as innovative 1-dimensional structures, exhibiting
smart properties useful for many application fields, and particularly in the framework of
nanoelectronics and optoelectronics. In particular, nanofibers made by organic semiconductor
materials such as conjugated polymers can constitute interesting building blocks of field-effect
transistors and miniaturized integrated photonic systems, where single fibers or controlled nanofiber
assemblies can generate, guide and detect light. Among the different possible nanofabrication
approaches, the electrospinning, that is based on the uniaxial stretching of concentrated polymer
solutions under an intense applied electric field, constitutes an especially flexible and highthroughput technique for the realization of organic nanofibers under continuous runs. In addition,
the high stretching related to the whipping instabilities of the organic materials in the electrified jets
can lead to anisotropic physical properties, polarized emission and enhanced conductivity of the
collected solid state nanofibers.
Here we review our recent results on the properties of electrospun polymer nanofibers made
by organic semiconductors. Optical properties, surface wettability, microfluidic and device
integration in field effect transistors are investigated highlighting the enormous potentiality of nextgeneration polymer nanostructures for application as novel nanoscale light-sources and buildingblocks for nanoelectronics.
Acknowledgement: Research performed in the framework of the FIRB Project
RBFR08DJZI “Futuro in Ricerca”.
Corresponding author:
Luana Persano at National Nanotechnology Laboratory of Istituto Nanoscienze-CNR, via Arnesano, I-73100 Lecce,
Italy
80
Metal-ion mediated surface functionalization of HOPG: Dense SAMs assembly
and soft electronic coupling
Paolo Petrangolini †‡, Andrea Alessandrini †‡ and Paolo Facci †
†Centro S3, CNR-Istituto di Nanoscienze, Via Campi 213/A, 41125 Modena, Italy
‡Department of Physics, University of Modena and Reggio Emilia, Via Campi 213/A, Modena, Italy
HOPG could be an excellent substrate for the study of biological system by Scanning Probe
Microscopy, like STM or AFM. This is mainly due to its flatness and conductivity. Furthermore,
from a surface chemistry standpoint, it shares its properties with graphene. However, its
hydrophobicity doesn’t allow using this substrate when hydrophilic molecules have to be deposited.
Moreover, the chemical functionalization of the HOPG surface is prevented by its strongly inert
nature.
Interaction of HOPG surface with ions in an electrochemical cell can modify the surface features of
HOPG and it allows using this modified surface as a platform for the formation of self assembled
monolayer (SAM). Furthermore, such an approach can enable for a soft functionalization that does
not alter the structural and electronic properties of the substrate itself.
Interaction of metal ions with the graphite has been extensively studied since several years (1,2).
Metal ions, like Li, K, Rb, Cs intercalate inside the graphite and form an ordered lattice on the
surface. STM images of the surface of graphite showed that an ordered lattice of ions is formed on
the HOPG surface.
Sirinsvasan et al. (3) have shown that a copper layer is formed on the HOPG surface when it is
immersed in a solution with copper ion concentration under potentiostatic control.
Here, as a first step towards the chemical functionalization of a HOPG surface, we used the same
technique to form a Cu layer; in a 0.1 M CaCl2 solution we applied a potential of -0.05 V vs SCE
for 1 minutes to the HOPG surface. Cyclic voltammetry after incubation, shows four typical peaks
caused by the interaction of copper ions with the HOPG surface. A XPS analysis confirmed the
presence of copper on the surface of HOPG after electrochemical deposition.
When the Octadecanethiol (OCD) molecules are deposited on a bare HOPG surface the
hydrophobic interactions assemble the molecules in a 2-D ordered structure lying flat (4,5). Instead
when we modify the HOPG surface with Cu ions, Cu affinity with the SH group of OCD allows
forming a SAM with the alkyl chains not in contact with the surface.
We then used Laviron’s theory to study the electrochemical properties of an OPV-HQ SAM on bare
HOPG and on a Cu-modified HOPG surface. Only on modified HOPG the redox peaks associated
with the HQ redox activity scale linearly with the voltage scan rate implying an immobilized layer
of redox molecules which interact electronically with the underlying HOPG substrate.
1- Stephen P.K. and Charles M. L. Physical Review B 1989, 40, 5856.
2- Stephen P.K. and Charls M. L. Physical Review B 1991, 44, 4064.
3- Sirinsvasan R. and Gopalan P. Surface Science 1995, 338, 31.
4- Tao Z., Zangguang C., Yiling W., Zhangjun L., Chanxuan W., Yiba L. and Ying F. Nano Lett.
2010, 10, 4732.
5- Quing-Min X., Li-Ju W., Chen W. and Chun-Li B. J.Phys. Chem. B. 2001, 105, 10465.
81
Efficient Visible Light-Induced Photocurrent in a Novel Bioinspired Hybrid
Bulk Heterojunction: Eumelanin-PSi
GUIDO MULA1, LAURA MANCA1, SUSANNA SETZU1 MARCO D’ISCHIA2 AND
ALESSANDRO PEZZELLA2
1 Dipartimento di Fisica, Cittadella Universitaria di Monserrato, Università degli Studi di
Cagliari, S.P. 8 km 0.7, 09042 Monserrato (Ca), Italy;
2 Dipartimento di Scienze Chimiche, Università degli Studi di Napoli Federico II, Complesso
Universitario Monte Sant'Angelo, Via Cintia, 4 - 80126 Napoli, Italy
The diffusion of photovoltaic devices has increased the need of new and more efficient solution for
the exploitation of solar energy. A great effort has been devoted to the development of new
materials, like organic semiconductors [1] and hybrid organic-inorganic materials [2-3]. Hybrid
material can join the advantages of both organic and inorganic materials, lowering production costs
and increasing device efficiencies. Dispersed heterojunction geometry [4-5], also known as bulk
heterojunction, consists mainly in two materials whose interface is deeply interpenetrating while the
two components remain in two separated phases. This geometry shows interesting ad-vantages in
the charge separation process. Mesoporous n+-type porous silicon, due to its columnar structure, is
thus a natural candidate for the fabrication of dispersed heterojunctions.
In this work we study a hybrid material realized by impregnating a porous silicon matrix with
eumelanin, the most common form of biological melanins, a class of natural pigments responsible
for the colorations of human skin and hair which have a significant socio-economic and biomedical
relevance, encompassing racial pigmentation, skin photoprotection, sun tanning and pigmentary
disorders. Moreover, eumelanins display a quite unusual set of phys-icochemical properties such as
broadband monotonic absorption in the UV-visible [6].
The effect of the introduction of eumelanin in the porous Si pores is discussed and a comparison of
the spectral differences in the photogenerated current for empty and impregnated porous Si layers is
presented. With respect to PSi alone, the presence of eumelanin significantly extends the useful
spectral range for optical absorption and photocarrier generation with a significant increase of
photocurrent generation towards the low energy part of the visible spectrum.
This result also provides the first evidence of the ability of eumelanin as a photoconverter. Further
studies are in progress to improve the reproducibility of the electrical behavior and to obtain a
structural characterization of the impregnated samples.
______
1.
B. Kippelen, J.-L. Brédas, Energ. Environ. Sci. 2, 251 (2009).
2.
T.-P. Nguyen, Surf. Coat. Tech. 206, 742-752 (2011).
3.
S. Günes, N.S. Sariciftci, Inorg. Chim. Acta 361, 581-588 (2008).
4.
Q. Wang, M.R. Page, E. Iwaniczko, Y. Xu, L. Roybal, R. Bauer, B. To, H.-C. Yuan, A.
Duda, F. Hasoon, Y.F. Yan, D. Levi, D. Meier, H.M. Branz, T.H. Wang, Appl. Phys. Lett. 96,
013507 (2010).
5.
H. Hoppe, N.S. Sariciftci, J. Mater. Res. 19, 1924-1945 (2011).
6.
P. Meredith, T. Sarna, Pigm. Cell Res. 19, 572-594 (2006).
82
Simulating azobenzene self assembling monolayers on gold surfaces
Silvio Pipolo, Enrico Benassi*, Stefano Corni*
Dept. of Physics, Università di Modena e Reggio Emilia, S3 center, CNR NANO, Modena
* S3 center, CNR NANO, Modena
The photoisomerization process of azobenzene has been widely studied both in solution and on
metal surfaces[1,2]. Because of its efficiency and controllability it can be exploited to set up tools
for controlling the movement of nano-objects with light. Recently, the development of classical [3]
and semiclassical [4] computational approaches to the study of this process in solution has
prompted us to optimize a dedicated classical force field for thio-azobenzenes, in order to extend
these investigations to azobenzene self-assembling monolayers (azo-SAM). The optimization
procedure and some preliminary results concerning structural properties of the azo-SAM on
Au(111) will be presented and discussed. Regarding the methodology, a detailed sampling of the
potential energy surface (PES) has been done by means of Quantum Mechanical (QM) methods,
then force field parameters have been obtained by minimizing the difference between the QM-PES
sample and the same PES sample calculated at a Molecular Mechanics level (MM-PES). In
addition, normal mode analysis have been used for the validation of the parameter set. Finally a
computational procedure capable to simulate an experimental investigation on the mechanical
stiffness of the monolayer has been set up. Computational results and approximations inherent in
the model will be presented and a comparison with available experimental data will be discussed[5].
[1] G. Pace, V. Ferri, C. Grave, M. Elbing, C. von Hanisch, M. Zharnikov, M. Mayor, M.A. Rampi,
P. Samorì, Proc. Nat. Acc. Science 2005, 104, 9937.
[2] V. Ferri, M. Elbing, G. Pace, M.D. Dickey, M. Zharnikov, P. Samorì, M. Mayor, and M.A.
Rampi, Angew. Chem. Int. Engl. Ed. 2008, 47, 3407.
[3] G. Tiberio et al., Chem. Phys. Chem. 2010, 11, 1018.
[4] T. Cusati, G. Granucci, M. Persico, J. Am. Chem. Soc. 2011, 133, 5109.
[5] E. Tirosh, E. Benassi, S. Pipolo, M. Mayor, M. Valasek, V. Frydman, S. Corni, S. Cohen,
Beilstein J. Nanotechnol. 2011, 2, 834.
Corresponding author: Silvio Pipolo, Università di Modena e Reggio Emilia, via G. Campi 213/a, 41125, Modena, mail:
[email protected]
83
Perylene derivatives functionalized with thiadiazole rings:
synthesis and electronic properties in OFET devices
Laura Ricciotti, Antonio Carella, Roberto Centore, Antonio Roviello, Mauro Causà
Mario Barra*, Francesca Ciccullo*, Antonio Cassinese*
Department of Chemistry, University of Naples ”Federico II”, Via Cinthia, I-80126 Naples, Italy
*CNR-SPIN and Department of Physics Science, University of Naples “Federico II”, Piazzale
Tecchio 80, 80125 Naples, Italy
Over the past decade, organic semiconducting materials have attracted much attention due to their
potential use in the field of organic electronics. Particularly, perylene-3,4,9,10-tetracarboxylic acid
diimide (PDI) derivatives are among the most promising and versatile n-type semiconductors due to
their high electron affinity, their remarkable chemical stability, their outstanding optical and
electronic properties and the considerable variety of possible chemical functionalization.(1,2) The
excellent charge transporting character of PDI is favorable for organic thin-film transistors (OTFT)
applications due to the rapid and effective electron transfer process. (3,4)
We report here on new PDI derivatives functionalized at the imide nitrogen with a thiadiazole
group, their chemical diagrams are shown in Figure 1.
The introduction of alkylthiadiazole groups
as electron withdrawing moieties into the
PDI scaffold has been chosen as a strategy
to possibly improve the performances of
PDI derivatives in n-channel FETs.5
Moreover, the functionalization of perylene
with the thiadiazole heterocycle is
Fig. 1. Molecular structure of PDI derivatives
compatible with a planar conformation
whereas an hexatomic ring would probably
induce a twist around the imide bond, lowering the electron transfer.
Successively, the synthesized PDI derivatives were deposited both by evaporation and spin-coating
techniques on suitable substrates for the fabrication of n-channel OTFT. The electrical
measurements have been carried out using devices with a bottom contact configuration, using as
gate dielectrics SiO2 or SiO2 functionalized with a HMDS (1,1,1,3,3,3-hexamethyldisilazane)
monolayer.
We have shown, through a carefully morphological and electrical investigations, that both PDI-T1
and PDI-T2 molecules can be used to fabricate n-type transistors able to work even under ambient
conditions. PDI-T1 evaporated films exhibited in vacuum a maximum mobility of 0.016
cm2/volt·sec which is comparable with the best values measured for PDI-8CN2 transistors realized
by evaporation on the same bottom-contact bottom-gate structure. 6
1.
K. Vasseur, C. Rolin, S.Vandezande, K. Temst, L. Froyen, P. Heremans, J. Phys. Chem., 115 (2010) 2730-2737.
2.
T. Schnitzler, C. Li, K. Mullen, Helvetica Chimica Acta, 92 (2009) 2525-2531.
3.
P. R. L. Malenfant, C. D. Dimitrakopoulos, J. D. Gelorme, A. Curioni, W. Andreoni, Applied Physics Letters,
2002, 80, 2517-2519.
4.
B. A. Jones, M. J. Ahrens, M. H. Yoon, A. Facchetti, T. J. Marks, M. R. Wasielewski, Angew. Chem. Int. Ed.
2004, 43, 6363-6366.
5.
H. Pang, P. J. Skabara, D. J. Crown, W. Duffy, M. Heeney, I. McCulluch, S. J. Coles, P. N. Horton, M. B.
Hursthouse, Macromolecules, 2007, 40, 6585-6593.
6.
M. Barra, F. V. Di Girolamo, F. Chiarella, M. Salluzzo, Z. Chen, A. Facchetti, L. Anderson, A. Cassinese, J. Phys.
Chem C 114, 20387 (2010).
Corresponding author: [email protected]
84
Towards the docking of DNA on surfaces: electronic structure of guanine and
cytosine on Au(111)
Marta Rosa*†, Stefano Corni† and Rosa Di Felice†
*Dipartimento di Fisica, Università di Modena e Reggio Emilia, Via Campi 213/A, 41125 Modena,
Italy
†Centro S3 – CNR Istituto di_Nanoscienze, Via Campi 213/A, 41125 Modena, Italy
Docking simulations are a powerful tool to predict the structures and orientations of interacting
proteins and one would like to tackle the DNA—surface interaction in the same manner. To this
aim, we conceived a multi-level computational scheme to sample different length and time scales at
different levels.
The multi-step computational protocol includes the following principal steps: (1) force-field
parametrization for DNA-surface interaction based on density functional theory (DFT) results of
DNA bases on surfaces; (2) classical molecular dynamics (MD) simulations with the developed
force fields of entire DNA molecules on substrates; (3) docking simulations based on scoring
functions derived from the MD trajectories/energetics and on a designed tool to take into account
the surface geometry in docking codes in a continuum solvent [Kokh, D. B.; Corni, S.; Winn, P. J.;
Hoefling, M.; Gottschalk, K. E.; Kay, E.; Wade, R. C. ProMetCS: J. Chem. Theory Comput. 2010,
6, 1753–1768.]. The most representative docked structures can then be refined with MD.
Furthermore, one can go back to step (1) for a small part of the system if electronic structure
information is desired.
The first thing to do in this approach is the understanding and description of the interaction between
the DNA chain and the surface. Using a recent implementation of VDW-DF functional in quantumespresso (www.quantum-espresso.org), we include van der Waals interactions in the study of single
DNA bases on the Au(111) surface.
We present the results obtained for Cytosine on Au(111), comparing different orientations ad
different adsorption sites to find the minimum energy configuration and the correct interaction
parameters. We also present a discussion of the relevance of van der Waals interactions. We
comment on the implication for DNA/Au force field parametrization.
Calculations were performed for the molecule adsorbed with the molecular plane both parallel and
perpendicular to the metal surface: we find a rather flat energy landscape for different adsorption
sites and molecular orientations. The comparison between results obtained with and without the
vdW interaction reveals a fundamental change of the vdW-DF picture relative to DFT: when the
vdW interaction is taken into account the molecule flat on the surface is not even a local minimum,
which instead was found in all previous works. Starting from a flat adsorption geometry, the
molecule eventually tilts at a small angle. The most favorable condition is, however, a vertical
adsorption configuration.
85
NANOSTRUCTURED PENTACENE/PCBM INTERFACE FOR ORGANIC
SOLAR CELL.
a
Andrea Radivoa, b*, Enrico Sovernigoa , Simone Dal Zilioa, Massimo Tormena,c
CNR - IOM Laboratorio TASC, S.S. 14 km 163.5 Basovizza - 34149 Trieste - Italy
b
Università di Trieste, Piazzale Europa 1 - 34127 Trieste - Italy
c
ThunderNIL s.r.l., Via Ugo Foscolo 8 - 35131 Padova - Italy
Thin-film photovoltaic (PV) cells based on the bulk hetero-junction of organic materials reached a
record efficiency of 8.3% 1 and have the potential to become a lower-cost alternative to amorphous
silicon. Some of the issues related to the intrinsic properties of generation, separation and transport
of charges, may be addressed not just by working on the details of the chemistry and processing of
the organic/fullerenes materials, but also by implementing new cell architectures organized and well
controlled down to the nanoscale. The present work is based on the conviction that the latter
approach, complementary to that focused on the improvement of the intrinsic properties of the
materials, will substantially contribute to the progress of this field of applied research. In particular
we recently realized a nano-interdigitated pentacene-PCBM structure, morphology that is indicated
as the optimal for an organic PV cell2, with an integrated nanostructured hole collection path. This
structure was obtained starting with the realization by nanoimprinting of a high form factor
nanostructured contact layer in PEDOTT:PPS for holes collection, followed by a conformal
deposition of thermal vacuum evaporated pentacene and finished by a filling of the structure with
PCBM by solution processing. As future work we intend to test this structure in an operative PV
cell and tune process and structures dimensions to demonstrate the usefulness of nanoarchitectures
in organic photovoltaics.
*Corresponding author: [email protected]
1
2
Konarka Inc., NREL certified measure. M. A. Green et al., Prog. Photovolt: Res. Appl.; 19 (2011) 84–92.
FanYang and Stephen R. Forrest. Acs Nano vol 2 n°5 1022-1032 (2008)
86
Interface electronic structures of large dipolar organic molecules on metal
substrates: computational methods for the high- and the low-coverage regimes.
Aleksandrs Terentjevs*, Eduardo Fabiano*, Fabio Della Sala*+
*National Nanotechnology Laboratory (NNL), Istituto Nanoscienze-CNR,
Via per Arnesano 16, I-73100 Lecce, Italy
+
Center for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia,
Via Barsanti, I-73010 Arnesano, Italy
Self-assembled monolayers (SAM) of polar organic molecules are often used in surface science and
molecular electronic applications to modulate the surface electronic properties of metal electrodes.
Here we investigate the interfacial electronic structure of the dipolar organic semiconductor vanadyl
naphthalocyanine (VONc) on Au(111) in a combined computational and experimental approach to
understand the role of the permanent molecular dipole moment on energy-level alignment at this
interface. Calculations have been performed within a first-principles plane-wave (PW) Density
Functional Theory (DFT) approach corrected for dispersion interactions. Results show a molecular
deformation upon adsorption but no strong chemical bond formation. Ultraviolet photoelectron
spectroscopy measurements show a considerable
workfunction change of -0.73 eV upon growth of
the first full monolayer, which is well reproduced
by the DFT calculations. This shift originates from
a large electron density “push-back” effect at the
gold surface, whereas the large out-of-plane
vanadyl dipole moment plays only a minor role.
To consider the sub-monolayer regime, where PW
calculations are too expensive, we report VONc
results[2] based on the SPICE (Self-consistent
Periodic Image-Charges Embedding) method [3],
which is based on an atomic orbital electrostatic
embedding scheme and allows to compute the
SAM depolarization at any coverage and beyond
conventional DFT methods.
The SPICE method have been also extended [2] to
study molecular excitations in SAMs. This
approach couples a time-dependent DFT approach with the SPICE embedding scheme and allows to
study the excited-state properties of individual molecules embedded into a SAM as well as the
dependence of the excited-state properties on the SAM's geometry and coverage. Results will be
presented for VONc and AlQ3 to illustrate the influence of the SAMs structure on the excited-state
properties.
[1] A. Terentjevs, M. P. Steele, M. L. Blumenfeld, N. Ilyas, L. L. Kelly, E. Fabiano, O. L.A. Monti,
F. Della Sala, J. Phys. Chem. C 115, 21128 (2011).
[2] A. Terentjevs, E. Fabiano, F. Della Sala, Theor. Chem. Acc. C 131, 1154 (2012).
[3] M. Piacenza, S. D'Agostino, E. Fabiano, F. Della Sala, Phys. Rev. B 80, 153101 (2009).
87
Supersonic Molecular Beam Deposition of α-Sexithiophene:
because energy matters!
M. Tonezzer1, T. Toccoli1, S. Gottardi2, E. Rigo3, P. Bettotti3 and S. Iannotta1
1
IMEM-CNR Istituto Materiali per Elettronica e Magnetismo,
Parco Area delle Science 37/a, I-43100 Parma, Italy
2
Zernike Institute for Advanced Materials, University of Groningen, The Netherlands
3
Laboratorio Nanoscienze, Dipartimento di Fisica, Università di Trento
Oligothiophenes are an interesting family of semiconducting pi-conjugated molecules, used to study
the growth of poly-crystalline organic thin films and to fabricate high performance organic devices
for several applications. The small size of such fundamental building blocks helps the investigation
of their self assembly to understand the forces involved. This could permit to minimize the rise of
different grains or domains inside the thin film. Such boundaries hinder different properties such as
the charge carrier mobility inside the organic devices, decreasing their performances.
Supersonic molecular beam deposition, the innovative technique we are using in the NanoScience
Lab of IMEM, can achieve unprecedented results thanks to a much higher control on the deposition
beam [1,2]. A proper setting of the source parameters allows to finely tune the molecules kinetic
energy, the main factor affecting the way the molecules assembly on the substrate [3].
In this contribution we relate on our investigations concerning the growth of α-sexithiophene on
silicon oxide substrate. We studied sexithiophene growth as a function of substrate temperature,
substrate wettability and especially kinetic energy of the impinging molecules [4]. Each of these
parameters has a different effect on the growth of the molecular thin film, in particular on the size
and shape of the sub-monolayer islands.
Optimizing these parameters in order to obtain the largest islands and minimize the grain
boundaries among them, we also deposited some thicker films which have been used to fabricate
several arrays of organic field effect transistors. The better arrangement of the first monolayer
drives in this case a quasi-layer-by-layer growth which produces wide, smooth and regular terraces.
The wider islands and the lower grain boundary density lead to much better performance: a field
effect mobility average value of 1.5·10-1 V∙cm-1∙s-1, twice higher than the best values in literature up
to now.
This work was financially supported by the Fondazione CARITRO Project “NanoSmart”.
Corresponding author: M. Tonezzer, via alla Cascata 56/C, Povo (TN) Italy. Tel: 0461 314828; Fax: 0461 314875;
Email: [email protected].
[1] R. Ruiz et al., Pentacene thin film growth, Chem. Mater. 16 (2004) 4497.
[2] T. Toccoli et al., Supersonic molecular beams deposition of a-quaterthiophene: Enhanced growth control and
devices performances, Org. Elec. 10 (2009) 521-526.
[3] S. Iannotta et al., Supersonic molecular beam growth of thin films of organic materials: A novel approach to
controlling the structure, morphology, and functional properties, J. Polym. Sci. B 41 (2003) 2501.
[4] Y. Wu et al., Controlling the Early Stages of Pentacene Growth by Supersonic Molecular Beam Deposition, Phys.
Rev. Lett., 98 (2007) 076601.
88
Charge transfer at the interface between Sexithiophene (T6) and N,N’-bis (noctyl)- dicyanoperylenediimide (PDI-8CN2) Heterostructures investigated by
UPS measuremnts.
M.Barra, F. Ciccullo, A. Cassinese,
CNR-SPIN and Dipartimento di Fisica Università di Napoli Federico II, Napoli,Italy
L. Aversa, R. Verucchi, S. Iannotta
Istituto dei Materiali per l’Elettronica ed il Magnetismo, IMEM–CNR, Via alla Cascata 56/C –
Povo, 38123 Trento, Italy
We report on the observation of an interfacial charge transfer effect in high quality Sexithiophene
(T6)/ N,N’-bis (n octyl)-dicyanoperylenediimide (PDI-8CN2) heterostructures, composing the
active channels of field-effect transistors (HeOFETs). Bilayer with different T6 and Pdi-8CN2
thicknesses have been realized and characterized by means of both electrical characterization, AFM
and ex-situ Ultraviolet Photoemission spectroscopy (UPS, with HeI and HeII photons). Bulk films
of T6 showed HOMO and (calculated) LUMO energy positions basically aligned to literature
results, while PDI-8CN2 energy levels differ from the expected configuration, with the HOMO
being 2.8eV below the Fermi edge, in principle making possible the matching between the T6HOMO and PDI-8CN2-LUMO levels. Indications of charge transfer at organic/organic interface
have been obtained by means of both electrical characterization and UPS analysis. In comparison
with single layer (unipolar) devices, the electrical response (output and transfer-curves) of
HeOFETs shows the presence of ambipolar transport, a considerable enhancement of the active
channel conductivity the shift of the threshold voltages and a negative transconductance behaviour
probabably related to a good matching between the HOMO value of the T6 with the LUMO value
of the PDI8CN2. Different configurations will be discussed, ranging from bulk thin films of
materials on device substrate, to different interfaces and bi-layers: the energy level scheme
constructed from UPS data will be presented together with a possible implication of different
phenomena at surfaces, as interface dipoles or band bending.
89
CELL BIOCOMPATIBILITY AND ELECTRICAL OPERATION IN
CELLULAR CULTURE MEDIUM OF N-TYPE ORGANIC TRANSISTORS
D.Viggiano*, M. Barra, R. Di Capua*, F. Di Girolamo, F. Santoro, M. Taglialatela* and A.
Cassinese
CNR-SPIN and Department of Physics Science, University of Naples Federico II, Naples
*Health Sciences Department, University of Molise, Campobasso
The possibility that organic field-effect transistors (OFET) can be applied in bio-sensing fields
depends largely on the availability of aromatic compounds displaying good biocompatibility
features and quite stable charge transport properties in aqueous ionic solutions. In this contribution,
we report about the cellular biocompatibility and the electrical response in the ionic medium
DMEM, commonly employed for in-vivo cell cultivation, of n-type OFET based on Perylene
Diimide molecules. N,N’–bis(n-octyl)-1,6-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI8CN2) and N,N0-1H,1H-perfluorobutyl-dicyanoperylenediimide (PDI-FCN2) films were
evaporated on highly doped Silicon (Si++)/SiO2 substrates provided of gold electrodes. The cellular
biocompatibility was tested by analyzing the adhesion and viability of two different cell lines:
human epithelial HeLa cells and murine neuronal F11 cells. The surfaces of uncovered SiO2
substrates and Sexithiophene (T6) films were used as testing controls. Results showed that,
although at high concentration these organic compounds are toxic in solution, if they are presented
in form of film, cell lines can attach and grow on them. In order to investigate the electrical stability
of PDI_8CN2 and PDI_FCN2 transistors in the DMEM liquid, low-voltage operation devices, able
to strongly reduce the influence of Faradaic currents coming from the electrical operation in an
highly ionic environment, have been fabricated on 35 nm thick SiO2 layers. According to the
results of this study, the structural and electrical properties of the film regions near the source-drain
electrodes are the most critical in order to improve the operation stability of these devices.
Corresponding author: dr.Davide Viggiano, Health Sciences Department, University of Molise, 86100, Campobasso,
email:[email protected]
90
Monitoring drug induced cellular stress by organic electrochemical transistors.
A. Romeoa)*, G. Tarabellaa), N. Coppedèa), R. Moscaa), R. Alfierib), P. Petroninib) and S. Iannottaa).
a)
b)
IMEM-CNR, Parco Area delle Scienze 37/A - 43124, Parma, Italy.
Experimental Medicine Dep, Experimental Oncology Section, Parma, Italy.
Organic electronic materials are gaining more and more attention as devices ideally suitable to
interface and monitor biological and biomedical processes [1]. In particular, organic
electrochemical transistors (OECTs) are promising disposable cell-based biosensors [2] for in vitro
or in vivo measurements, due to their flexibility, low cost, easy fabrication and biocompatibility.
Our contribution aims to assess the detection of cellular stress induced by drugs that will make
OECTs a more meaningful and useful tools to reveal real-time cellular responses a field of growing
interest and very strong impact [3,4]. Our devices, with an active layer made of PEDOT:PSS, were
firstly characterized in several culture media, showing relatively stable and reliable operation also in
biological environment. Then cell cancer lines were used to test the capability of our OECTs to
detect cellular responses induced by drugs and other chemical substances. Parallel checks were
carried out by optical microscopy, to associate directly the OECT responses to the optical
observations.
[1] M. Berggren and A. Richter-Dahlfors, Adv. Mater. 2007, 19, 3201–3213.
[2] P. Lin , F. Yan , J. Yu , H. L. W. Chan , and M. Yang, Adv. Mater. 2010, 22, 3655–3660.
[3] S. Y. Yang , B. N. Kim , A. A. Zakhidov , P. G. Taylor , J.-Kyun Lee , C. K. Ober , M. Lindau ,
and G. G. Malliaras, Adv. Mater. 2011, 23, H184–H188.
[4] A. M. D. Wan, D. J. Brooks, A. Gumus, C. Fischbach and G. G. Malliaras, Chem. Commun.,
2009, 5278–5280.
*Corresponding author: IMEM-CNR, Parco Area delle Scienze 37/A, 43100 Parma, Italy, tel: +39 0521 269224, email:
[email protected].
91
Large scale micro- and nano- structuring of azobenzene-conatining polymer
films.
Antonio Ambrosio1,*, Andrea Camposeo2, Fabio Borbone3, Dario Pisignano2, Antonio Roviello3,
Pasqualino Maddalena1
1
CNR-SPIN U.O.S. Napoli and Dipartimento di Scienze Fisiche, Università degli Studi di Napoli
Federico II, Complesso Universitario di Monte Sant’Angelo, Via Cintia, I-80126, Napoli, Italy
2
NNL, Istituto Nanoscienze-CNR and Dipartimento di Matematica e Fisica “Ennio De Giorgi”, via
Arnesano, I-73100, Lecce, Italy
3
Dipartimento di Chimica, Università degli Studi di Napoli Federico II, Complesso Universitario di
Monte Sant’Angelo, Via Cintia, I-80126, Napoli, Italy
The possibility of fully-optical structuring of azo-polymers films surface has recently attracted
interest for its potential application in optoelectronics. For instance, Ubukata et al. [1] have reported
on the fabrication of a double-layered distributed feedback (DFB) laser based on a diffractive
element constituted by a one-dimensionally structured azo-polymer, obtained by exposing to the
interference pattern of two visible laser beams from an Argon ions laser.
Mixing active compounds with azobenzene molecules or polymers can represent a strategic way for
obtaining systems that combine patterning capability with light emission. Our results show the
possibility to pattern the mixture by means of a laser scanning technique, thus realizing
photoluminescent features whose shapes and spatial distribution can be arranged by exploiting the
light-polarization dependence of the mass migration process. The mass migration phenomenon
occurring on the free surface of azobenzene-containing polymers illuminated by light of appropriate
wavelength is employed to pattern polymeric films constituted by an azo-polymer containing a
photoluminescent chromophore[2].
Furthermore, we report about the possibility to drive mass migration into an azo-based polymer by
means of two-photon absorption. Our azo-chromophore, characterized by a symmetric donoracceptor-donor π-conjugated structure, is expected to show good TPA features. It is, in fact, well
known that a symmetric distribution of groups into a molecule may favour TPA properties due to
symmetric charge transfer from the end of the molecule to the middle. The samples we used for
TPL are high optical quality films, with thickness of 550 nm, prepared by spin coating a pyridine
solution (polymer concentration 5% wt) on glass coverslips [3].
By this way we have realized structures down to 250 nm wide employing the diffraction limited
spot of the 800 nm wavelength pulsed laser, far below the half-wavelength diffraction limit of the
focused laser beam.
The research leading to these results has received funding from the FP7/ 2007-2013 under grant
agreements N. 264098 – MAMA.
[1] T. Ubukata, T. Isoshime, and M. Hara, Adv. Mater. 17, 1630 (2005);
[2] A. Ambrosio, E. Orabona, P. Maddalena, A. Camposeo, M. Polo, A.A.R. Neves, D. Pisignano,
A. Carella, F. Borbone, A. Roviello, Applied Physics Letters 94, 011115 (2009); Ambrosio, A.
Camposeo, A. Carella, F. Borbone, D. Pisignano, A. Roviello, P. Maddalena, Journal of Applied
Physics 107, 083110 (2010); [3] A. Ambrosio, P. Maddalena, A. Carella, F. Borbone, A. Roviello,
M. Polo, A. A. R. Neves, A. Camposeo, and D. Pisignano, J. Phys. Chem. C 115, 13566 (2011)
Antonio Ambrosio ([email protected]), CNR-SPIN U.O.S. Napoli,
Dipartimento di Scienze Fisiche, Complesso Universitario di Monte Sant’Angelo, Via Cintia,
80126 – Napoli (Italy)
Corresponding author:
92
ZnO nanostructure Functionalization for electronic, gas sensing and
photovoltaic application
Nicola Coppedè*1, Marco Villani1, Roberto Mosca1, Laura Lazzarini1, Marco Nardi1, Salvatore
Iannotta1, Andrea Zappettini1 and Davide Calestani1
1
IMEM CNR Istituto dei Materiali per l' Elettronica ed il Magnetismo
Parco Area delle Scienze 37/A, 43124 Parma, Italy.
Organic–inorganic hybrid nanostructures are receiving considerable attention for the development
of “smart” materials with new tailored properties. The interaction between nanostructure and
organic molecules give rise to transduction effects, in charge and excitation exchange, that could
improve the electric properties of the material. A key iussue to obtain effective useful materials is
the control of the functionalization at the nanoscale. We approch the functionalization of ZnO
nanostructures in different ways. We selective functionalize ZnO nanostructures, with organic
oligomers, using Supersonic Molecular Beam Deposition (SuMBD), applying the directional
properties of the seeded supersonic beams. We used ZnO because of its ability to form controlled
nanostructures with semicondacting properties. We applied SuMBD to ZnO nanorods [1], which
present interesting advantages, especially in solar cells applications. First of all, ZnO nanorods
present a continuous crystalline structure, which could be grown on a conductive transparent metal
oxide (TCO) made ZnO doped with Aluminium (AZO) deposited directly on glass [2]. In such a
way, the structural homogeneity and crystalline properties are maintained all over the NR length,
allowing a continuous path for the electrons in the material. Using the directional properties of the
beam, a selective functionalization, only on one specific side of the nanorod, has been realized.
Moreover we used Vapour phase deposition to functionalize ZnO nanotrapods for gas sensing
application. It has already been demonstrated that the combined use of nanostructured metal oxides
and organic molecules improves the selectivity in gas sensing performances at least in the case of
TiO2 [3]. We realized gas sensor devices based on films of interconnected ZnO nanoterapods
opportunely functionalized by Titanyl Phthalocyanine. The aim is to combine the high surface area
ratio and the structural property of the crystalline structure of the ZnO nanoterapods with the
sensitivity of the interaction, meditated as a transducer, of the TiOPc molecule. The electronic
properties of the nanohybrid material results different from the single behavior of each component.
In Particular an enachement of more of one order of magnitude in the sensitivity for the hybrid
sensor respect to ZnO has been revealed at lower temperatures (100 °C and also at RT), proving the
effective role of the hybrid interface and opening new possibilities in hybrid applications.
[1]
M. C. Carotta, A. Cervi, V. Di Natale, S. Gherardi, A. Giberti, V. Guidi, D. Puzzovio, G.
Martinelli, M. Sacerdoti, D. Calestani, A. Zappettini, M. Zha, L. Zanotti, “ZnO gas sensors: a
comparison between nanoparticles and nanotetrapods-based thich films”, Sensors and Actuators B
137 (2009) 164-169
[2]
D. Calestani, M. Zha, L. Zanotti, M. Villani, A. Zappettini, Low temperature thermal
evaporation growth of aligned ZnO nanorods on ZnO film CrystEngComm, 13, (2011), 1707, D.
[3]
Siviero, N. Coppedè, A. Pallaoro, A.M. Taurino, T. Toccoli, P. Siciliano, S. Iannotta,
“Hybrid n-TiO2-CuPc gas sensors sensitive to reducing species, synthesized by cluster and
supersonic beam deposition”, Sensors and Actuators B 126 (2007) 214–220)
Corresponding author: Nicola Coppede Parco Area delle Scienze 37/A - 43124 Parma, Italy - Phone: +390521269217
[email protected]
93
Structure and electronic properties of self-assembled transition metal
phthalocyanines (M=Fe,Co,Ni,Cu,Zn) on the Au(110) surface
S.Fortuna*1,2, P. Gargiani4, M.G.Betti4, C.Mariani4, A.Calzolari3, S.Fabris1,2,
CNR-IOM DEMOCRITOS, Theory@Elettra group, S.S. 14, km 163.5, I-34149 Trieste, Italy
2
SISSA, Via Bonomea 265, I-34136, Trieste, Italy
3
CNR-Nano Istituto di Nanoscienze, Centro S3, I-41125 Modena, Italy
4
Dipartimento di Fisica, Università di Roma La Sapienza, Roma, Italy
1
The relative strengths interplay between intermolecular and molecule–substrate interactions
generally controls the pattern formed by surface-adsorbed self-organised molecules. However,
when the substrate can easily reconstruct upon molecular adsorption, a self-templating effect on the
metallic support can be observed.
This is the case for Fe-phthalocyanine (FePc) molecules adsorbed on the Au(110) surface.
STM imaging and low energy electron diffraction patterns show how FePc molecules can
selforganize into ordered chains along the [1-10] direction driving the formation of reconstructed
channels on the underlying Au substrate [1]. Density functional theory calculations reveal the
energetic origins of the molecule-driven substrate reconstruction, showing that a larger molecular
binding is achieved by first reorganizing the metal surface underneath the molecule.
The molecule-substrate interaction process further induces a rehybridization of the electronic states
localized on the central metal atom. By DFT calculations we clarify the effect and role of the
surface, acting as a fifth ligand on the FePc metallorganic states [2]. In addition, we perform a
systematic analysis on the first row transition metal MPc (M=Co,Ni,Cu,Zn) on the same substrate,
revealing the individual electronic features and the common trends. Since the function of molecular
overlayers at surfaces is strongly correlated to their structure, these results have implications in the
design of new metal/molecular interfaces.
[1] S.Fortuna, P.Gargiani, M.G.Betti, C.Mariani, A.Calzolari, S.Modesti, and S.Fabris,
J.Phys.Chem.C, 2012, 116(10), 6251–6258.
[2] M.G.Betti, P.Gargiani, C.Mariani, S.Turchini, N.Zema, S.Fortuna, A. Calzolari, and S.Fabris,
J.Phys.Chem.C, 2012, 116 (15), 8657–8663.
* [email protected] – http://www.sarafortuna.eu
94
Nano-granular Thin Films As Substrates For Protein Deposition
C. Toccafondi1, O. Cavalleri1, E. Barborini2, F. Bisio3 and M. Canepa1
CNISM and Physics Dpt., University of Genova, Genova, 16146, Italy;
2
Tethis S. p. A., Via Franco Russoli 3, 20143 Milan, Italy
3
CNR-SPIN Genova, Genova, 16152, Italy
1
Nanogranular (and nanoporous) thin films are a promising platform for bio-sensing applications [1].
Cluster-assembled nano-porous Au and TiO 2 thin films have been deposited onto Si substrates by
means of supersonic cluster beam deposition (SCBD) [2,3].
Previous knowledge about the surface and inner structure of nanogranular films is a pre-requisite
for the investigation of their response to the deposition of proteins in liquid environment. To this
end we have studied the optical, morphologic and electronic properties of both Au and TiO 2 films
using spectroscopic ellipsometry (SE), Atomic Force Microscopy (AFM) and X-ray Photoelectron
Spectroscopy (XPS).
AFM images revealed a characteristic surface roughness arising from the random stacking of the
spheroidal nanoparticles. The complex morphology of these cluster-assembled films introduces
some drastic changes in their optical properties, with respect to flat counterparts: SE data modeling
becomes thereby a particularly challenging task. Bruggeman Effective Medium Approximation (BEMA) was used in order to model the film roughness and the presence of nanopores [4-6], yielding
satisfactory fit results for both Au [7] and TiO 2 .
Recently we have studied the adsorption of Yeast Cytochrome c (YCC), a relatively small hemeprotein, on these nanogranular films using in situ SE measurements in aqueous solutions, extending
our research on protein deposition on ultraflat Au surfaces [8]. Differences between spectra taken
after and before the protein deposition show sharp features related to molecular absorptions of the
heme group, the so-called Soret band at about 410 nm. This peak appears in the same position
found for molecules in solution, suggesting that YCC native conformation is maintained upon
adsorption. A comparison between results obtained for YCC adsorption on Au and TiO 2 clusterassembled films will be shown and some initial modeling efforts will be also presented.
References
[1] ] R. Carbone et al., Biomaterials 27, 3221–3229 (2006);
[2] E. Barborini, P. Piseri, P. Milani, J. Phys. D: Appl. Phys. 32, L105 (1999);
[3] E. Barborini et al., Eur. Phys. J. D 24, 277–282 (2003);
[4] F. Bisio et al., Physical Review B, 80, 205428 (2009).;
[5] F. Bisio et al., J. Phys. Chem. C 114, 17591–17596 (2010);
[6] F. Bisio, M. Prato, E. Barborini, M. Canepa, Langmuir 27 (13), 8371(2011);
[7] C. Toccafondi et al., Bionanoscience 1(4), 210-217 (2011);
[8] C. Toccafondi, M. Prato et al., J. Colloid Interf. Sci. 364, 1, 125-132, (2011).
95
Organic Field-Effect Transistors as Organic Gauge for the study of the charge
injection across Self-Assembled Monolayers
S. Casalinia, S. Destrib, W. Porziob, A. Operamollae, F. Leonardic, C. Albonettia, A. Shehua, F.
Borgattia, M.C. Pasinib, F. Vignalib, C.A. Bortolottid, O.H. Omarf, L. Paltrinierid, G. Farinolae and F.
Biscarinia
a
Consiglio Nazionale delle Ricerche – Istituto per lo Studio dei Materiali Nanostrutturati (CNR-ISMN) via P. Gobetti
n. 101, 40129 Bologna, Italy
b
Consiglio Nazionale delle Ricerche – Istituto per lo Studio delle Macromolecole (CNR-ISMAC) via Bassini n. 15,
20133 Milano, Italy
c
‘‘Alma Mater Studiorum’’ Università di Bologna, Dipartimento di Chimica ‘‘G. Ciamician’’ via Zamboni n. 33,
40126 Bologna, Italy
d
Università degli Studi di Modena e Reggio Emilia, Dipartimento di Chimica, via Campi 183 I-41100 Modena (Italy).
e
Università degli Studi di Bari, Dipartimento di Chimica, via Orabona 4,I-70126 Bari, Italy
f
Consiglio Nazionale delle Ricerche - Istituto di Chimica dei Composti Oraganometallici (CNR-ICCOM), Dipartimento
di Chimica, via Orabona 4, I-70126 Bari, Italy
Organic Field-Effect Transistors (OTFTs) represent an important and promising new technology for
large area, flexible and disposable applications, like active matrix flexible displays, e-papers,
memories, sensors and bio-transducers.
The use of Self-Assembled Monolayers (SAMs) in the interface engineering has been largely
exploited for tuning the electrical performances of OFETs, modifying the chemical–physical
properties of interfaces involved in the charge-injection and transport of the charge carriers.
In particular, it was demonstrated that OFETs, after the source-drain functionalization by means of
alkanethiol-based SAM, respond as molecular gauge in saturation regime. The detailed features of
the trend of the charge mobility vs the number, n, of methylene units arise from a rather complex
interplay of interfacial morphology, molecular ordering, decrease of energy disorder, and charge
tunneling mediated by the SAM alkyl chain[1].
Here we use the same strategy for source-drain functionalization, exploiting two new set of
molecules (such as oligothiophenes and oligoarylenes, see Fig.1), capable to self-assemble on gold
surface. We have investigated how the electrical behavior is affected by the presence of these SAMs
in a real device (i.e. pentacene-based OFET) and its multi-parametric response enables us a detailed
characterization of the SAM properties in terms of tunneling decay coefficient[2], resistance drop
and critical voltage[3]. In conclusion, we proved that OFET can be considered as charge injection
organic gauge for the electrical characterization of SAMs placed in between metal electrode and
organic semiconductor.
Oligothiophenes
Oligoarylenes
HS
TD
HS
HS
S
TBD
HS
S
Fig.1 Drawing of oligothiophenes and
oligoarylenes backbones used for the sourcedrain functionalization.
TBM
HS
References:
[1] P.Stoliar, R. Kshirsagar, M. Massi, P. Annibale, C. Albonetti, D.M. Leeuw, F. Biscarini, J. Am. Chem. Soc.129
(2007), 6477-6484.
[2] S. Casalini, A. Shehua, S. Destri, W. Porzio, M.C. Pasini, F. Vignali, F. Borgatti, C. Albonetti, F. Leonardi,
F.Biscarini, Org. Electron. 13 (2012) 789-795
[3] S. Casalini, F. Leonardi, C.A. Bortolotti, A. Operamolla, O.H. Omar, L. Paltrinieri, C. Albonetti, G.M. Farinola and
F. Biscarini, J. Mat. Chem. DOI:10.1039/C2JM30838J
96
MAGNETICALLY ENHANCED MEMRISTOR
Mirko Prezioso1, Alberto Riminucci1, Ilaria Bergenti1, Patrizio Graziosi1 and Valentin A. Dediu1
1
Consiglio Nazionale delle Ricerche - Istituto per lo Studio dei Materiali Nanostrutturati (CNRISMN) via P. Gobetti 101, 40129 Bologna, Italy
The unrelenting demand for increased density of processing and storage elements in the field of
Information and Communication Technology (ICT) is clashing against fundamental physical
limitations. This calls for conceptually new solutions leading to innovative devices capable of both
storage and processing. Recently, architectures capable to meet these requirements have been
proposed which have the memristor as the sole building element[1].
We describe here an experimental achievement which adds conceptually new features to a standard
memristor principle[2]. We show that electrically controlled magnetoresistance[3] can be achieved in
organic devices by combining magnetic bistability, GMR effect[4], and memristive effects.
Moreover , this behavior leads to innovative and useful features for information processing. This
Magnetically Enhanced Memristor (MEM) is distinguished by a strong intermixture of the electrical
and the magnetic degrees of freedom leading to a magnetic modulation of memristance states
multitude.
In more details, the devices presented in this work consist of a 20 nm thick bottom LSMO
electrode, on which a layer of Alq 3 (with thickness ranging between 3 nm and 250 nm) is
evaporated. The top electrode consists of a 20 nm thick Co film, separated from the Alq 3 by a 2 nm
thick AlO x tunnel barrier.
These devices show the typical memristor fingerprint known as the pinched I-V hysteresis. The
electrical switching is driven by the applied voltage and are in the 1-3 V range. In the negative
branch the I-V features a well controllable NDR region which allows the selection of the
memristance state of the device by reaching the necessary voltage and then come back to zero.
By the electrical point of view the R off /R on ratio can reach up to 104 while the retention time is in
the order of days (at 100K). We also performed Write/Read/Erase/Read cycles for checking the
repeatability up to 14000 times.
The same devices, when operated at biases as low as -0.1 V, behaves also as a spin-valve and can
show a GMR effect of up to 22% (at 100K).
The most interesting effect is the dependence of the GMR effect on the memresistance state of the
memristor. Indeed, the higher is the resistance state the lower is the GMR amplitude. This, added to
the possibility of selecting the memristance state, leads to a controllable amount of GMR effect. We
present experimental results demonstrating 32 different resistance states with their corresponding
GMR amplitude.
Moreover we show that by using the programming voltage and the external magnetic field as inputs,
it is possible to obtain an AND logic gate with only a single MEM device.
97
Organic Schottky gated heterostructures
I. Gutiérrez Lezama1, M. Nakano 1,2, F. V. Di Girolamo 1,3,*, N. Minder 1, Z. Chen 4, A. Facchetti 4
and A. F. Morpurgo 1
1
. DPMC and GAP, Université de Genève, 24 quai Ernest Ansermet, CH1211 Geneva, Switzerland
2
. RIKEN-ASI, 2-1, Hirosawa, Wako, Saitama 351-0198, Japan
3
. CNR-SPIN and Department of Physics Science, University of Naples «Federico II», Naples, Italy
4
. CHEM, Northwestern University, 2145 Sheridan Road, Evanston IL, 60208
(*e-mail address : [email protected] ; phone: +390817682548)
Heterojunctions represent the building block in a wide class of innovative devices; in electronics,
for instance, they have paved the way for the realization of multipurpose field effect transistors (e.g.
ambipolar and light emitting). In this regard, a noticeable enhancement of the electrical
conductivity, even leading to metallic behaviour [1] has been demonstrated, resulting of particular
interest for applications; charge transfer has been invoked as the mechanism at the origin of this
behaviour. The problem has been widely investigated, mostly in the case of thin film devices [2],
but issues related to the morphology and to the individuation of the place where the carriers are
accumulated complicates the clarification of the transport mechanism. In our work we have
overcome these issues by carefully choosing the semiconductors and the device configuration. We
have focused our attention on organic single crystals, which represent a case study due to the high
reproducibility of their properties [3]. In the device configuration the heterostructure is formed by
PDIF-CN 2 and rubrene single crystals; rubrene is laminated on a chromium stripe, with which it
forms a Schottky barrier. The barrier and the low concentration of dopants in the rubrene guarantee
that charge carriers are solely accumulated in the PDIF-CN 2 . Transfer curves indicates that the
conduction is due to electrons; at lowering temperature, band-like behavior is observed down to less
than 150 K, with the electron mobility remaining as high as 1 cm2/Vs at 50 K in the best devices.
Furthermore, the charge carrier density at VG = 0 exhibits a linear temperature dependence, which
cannot be attributed to a thermal activated behaviour. The results can be explained using a simple
model accounting for the alignment of the rubrene HOMO band with the bottom of the LUMO band
of PDIF-CN 2 . Schottky gated heterostructures have been consequently demonstrated to be a
powerful tool for probing the electrical properties of semiconductors and allowed tuning the charge
carrier density at the interface between two organic semiconductors. Moreover, the band alignment
at the heterointerface modified, actually improving, the electrical properties of PDIF- CN 2 .
[1] H. Alves, A. S. Molinari, H. Xie & A. F. Morpurgo, Nature Materials 7, 574 (2008).
[2] Haibo Wang and Donghang Yan, NPG Asia Mater. 2, 69 (2010).
[3] Electronic properties of single-crystal organic charge transfer interfaces probed using Schottkygated hetrostructures, I.G. Lezama, M. Nakano , N. Minder , Z. Chen , F. Di Girolamo , A.
Facchetti, A. F. Morpurgo submitted to Nature Materials.
98
Atomistic simulations of sexithiophene-fullerene heterojunctions
Gabriele D’Avino*, Luca Muccioli*, Claudio Zannoni
Dipartimento di Chimica Fisica e Inorganica, University of Bologna, Italy
Understanding the supramolecular arrangement at organic-organic interfaces is a central issue in
organic photovoltaics, being this one of the key factors in determining device performances [1]. The
simulation of realistic heterojunctions can in principle be tackled by using classical atomistic
molecular dynamics, always keeping in mind that mimicking the experimental preparation
techniques is mandatory to produce realistic structures [2,3]. We focus here on the interface
between sexi-thiophene (T6) and fullerene (C60), a donor-acceptor system successfully employed
in organic photovoltaic devices [4] that also represents a model system for the most studied poly-3hexyl-thiophene-PCBM blend [5]. Molecular dynamics simulations performed on large systems
(>50k atoms) and spanning large timescales (20-100 ns), show that interfaces characterized by
different relative molecular orientations, can be obtained by following two different experimental
preparation procedures. In the vapor phase growth of T6 on the C60(001) surface, a film of standing
T6 is formed because of dominant intra-adlayer interactions, as already observed in the case of
pentacene/C60(001) [2]. On the contrary, when the heterojunction is prepared through a hightemperature annealing [6], T6 molecules orient parallel to the interface, as a result of the formation
of a smectic T6 mesophase with a planar homogeneous alignment at 600 K. The implications of
interface morphology on the charge separation energetics and on the charge mobility perpendicular
to the interface are also addressed.
[1] A. W. Hains, Z. Liang, M. A. Woodhouse, B. A. Gregg, Chem. Rev., 2010, 110, 6689.
[2] L. Muccioli, G. D’Avino, C. Zannoni, Adv. Mater., 2011, 23, 4523.
[3] D. Beljonne, J. Cornil, L. Muccioli, C. Zannoni, J.-L. Brédas, F. Castet, Chem. Mater., 2011, 23,
591.
[4] J. Sakai, T. Taima, K. Saito, Org. Electron., 2008, 9, 582.
[5] M. A. Brady, G. M. Su, M. L. Chabinyc, Soft Matter, 2011,7, 11065
[6] A. Pizzirusso, M. Savini, L. Muccioli, C. Zannoni, J. Mater. Chem., 2011, 21, 125.
Corresponding author: Gabriele D’Avino [email protected], Luca Muccioli [email protected] ,
Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, viale Risorgimento 4, 40136 Bologna (IT)
99
Thin film growth of pentacene on C60 (001) from vapor deposition simulations
Gabriele D’Avino*, Luca Muccioli*, Claudio Zannoni
Dipartimento di Chimica Fisica e Inorganica, University of Bologna, Italy
The growth of small molecule thin films on organic and inorganic substrates is regulated by several
parameters, and among these the chemical and physical properties of the target surface play a very
important role [1]. Here, with the help of atomistic modeling techniques, we attempt to predict the
mechanism of growth of pentacene on Buckminster fullerene, with an approach inspired by the
organic vacuum beam deposition technique.
To simulate the growth of pentacene on a C60 (001) surface we performed Molecular Dynamics
simulations within the NVT ensemble at T=500 K. The deposition of pentacene was mimicked by
inserting into the box a pentacene molecule every 250 picoseconds. Simulations predict [2] a quasi
2D layer-by-layer growth, assisted by a coverage-dependent reorientation mechanism, which is
expected to take place even in small (100-molecule) pentacene clusters. The resulting pentacene
thin film shows a structure remarkably different from the bulk phase one, suggesting the existence
of a polymorph induced by the peculiar structure of the C60 (001) surface [3].
The growth of pentacene on C60 (001) proceeds in two coverage-dependent steps: in the first,
pentacene molecules lay flat and disordered on the C60 free surface, with a steady growth of the
film height. In the second, pentacene molecules reorient perpendicular to the surface and assume a
crystalline packing, with incoming molecules positioning themselves at island edges. This
mechanism is governed by the fact that a pentacene molecule standing in a pentacene monolayer is
two to three times more stable than an isolated, flat one, condition necessary for a layer-by-layer
growth [4]. This study represents a significant progress towards demonstrating in full the growth
mechanism of organic crystals with atomistic simulations, and opens the way to systematic
investigations of organic semiconductor interfaces.
[1] R. Ruiz et al., Chem. Mater. 16, 4497 (2004)
[2] L. Muccioli, G. D’Avino, C. Zannoni, Adv. Mater. 23, 4532 (2011)
[3] D. B. Dougherty, W. Jin, W. G. Cullen, J. E. Reutt-Robey, S. W. Robey, Appl. Phys. Lett. 94,
023103 (2009)
[4] D. Choudhary, P. Clancy, R. Shetty, F. Escobedo, Adv. Funct. Mater. 16, 1768 (2006)
Corresponding author: Gabriele D’Avino [email protected], Luca Muccioli [email protected] ,
Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, viale Risorgimento 4, 40136 Bologna (IT)
100
Interaction of adenine with nanostructured silver surfaces
S. Caporali1*, M. Iakhnenko2,3, M. Muniz-Miranda1, M. Pagliai1, M. Pedio4, G. Pratesi5, N. Tsud6,
R. G. Acres3, K.C. Prince3, V. Schettino7
1
Dipartimento di Chimica, Università degli Studi di Firenze, Via della Lastruccia 3, 50019, Sesto
Fiorentino (FI), Italy.
2
Taras Shevchenko National University of Kyiv, Faculty of Physics, Department of Experimental
Physics, Kyiv, Ukraine
3
Sincrotrone Trieste, in Area Science Park, Basovizza, (Trieste) 34149 Italy
4
CNR-IOM, TASC, in Area Science Park, Basovizza (Trieste) 34149, Italy
5
Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via La Pira 4, 50123
Firenze (FI), Italy
6
Charles University, Faculty of Mathematics and Physics, Department of Surface and Plasma
Science, V Holešovičkách 2, 18000 Prague, Czech Republic
7
European Laboratory for Non-Linear Spectroscopy (LENS), Università degli Studi di Firenze, Via
N. Carrara 1, 50019, Sesto Fiorentino (FI), Italy
The adsorption of biological molecules on surfaces of metals is of great importance owing to the
large number of possible applications in medical, biological and technological fields. In recent years
the use of coin metal nanoparticles to enhance the Raman signal of organic molecules (SERS) has
attracted much attention. Many good reasons account for this; the technique is non-destructive, has
a wide spectral range suitable for detecting several organic species, minimal sample preparation is
required and, last but not least, the instrumentation is rather simple, and can be miniaturized,
allowing its use in extraterrestrial applications. For the detection of traces of life, both extant and
extinct, in extraterrestrial environments such as the surface of Mars, comets or asteroids, SERS
could constitute a powerful investigation tool, potentially capable of improving our understanding
of whether and how primitive forms of life originated in extraterrestrial environments.
Since the SERS effect is strictly related to chemisorption phenomena, it is of fundamental
importance to know how SERS-active biomolecules, interact with the surface of the metal
nanoparticles and what are the atoms involved in such interface processes. By means of
photoemission (PES) and x-ray absorption (NEXAFS) measurements, we investigated the
absorption geometry of adenine on a “real” substrate consisting of chemically prepared silver
lamina.
Nitrogen NEXAFS data were collected varying the angle from 90° (normal incidence) to 10°
(grazing incidence) observing, a clear trend of the π resonance intensity as a function of the electric
field. Different surface models (pillar-like, grains, different local substrate symmetries with and
without homogeneous distribution of the molecular tilt, etc) were evaluated in order to better
simulate the sample surface. Independently from the adopted model the adsorption geometry was
invariably tilted. Statistical analysis indicates the most likely geometry is an angle of about 15°± 7°
between the plane of the molecule and the substrate surface. These observations agree well with
theoretical calculations and recently published SERS observations.
Furthermore, the angular dependence of the XPS data are in accordance with this type of
geometry, even though the presence of atmospheric contaminants, as well as the surface roughness,
contributes to peak broadening, impairing the unambiguous interpretation of these data.
Corresponding author: Dr. Stefano Caporali, Dipartimento di Chimica, Via della Lastruccia 3,
50019 Sesto Fiorentino, Italy, Phone: +39 055 4573146, Fax: +39 055 4573120, e-mail:
[email protected]
101
Real-time structural and electrical investigation of PDI8-CN2 based OFET.
F. Liscio1*, S. Milita1, C. Albonetti2, A. Shehu2, S. D. Quiroga2, Fabio Biscarini2,
K. A. Broch3, F. Schreiber3, S. Kowarik4
1
CNR- Instituto per la Microelettronica e Microsistemi (IMM), I-40129 Bologna (Italy)
CNR- Instituto per lo Studio dei Materiali Nanostrutturati (ISMN), I-40129 Bologna (Italy)
3
Institut fuer Angewandte Physik, Universitaet Tuebingen, Tuebingen (Germany)
4
Institut für Physik, Humboldt-Universität zu Berlin Newtonstr. 15, D-12489 Berlin (Germany)
2
Semiconductor thin-film devices based on organic molecules are of great interest for the
development of high performance organic field effect transistors (OFETs) and organic light
emitting diodes (OLEDs), as well as to underscore fundamental charge transport effects in
molecular solids. Among the n-type organic molecules, perylene derivatives are very promising. In
particular,
the
PDI-8CN2
molecules,
N,N’-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis
(dicarboximide), has been reported to allow the fabrication of OFETs with excellent electrical
performance (high-mobility: 0.16-0.6 cm2 V-1s-1) and remarkably high stability in air [1, 2, 3]. In
this system, the charge mobility depends on the overlap between π-π orbital’s of vicinal molecules,
which is mainly influenced by the structure and morphology of the first layers of organic film at the
interface with the dielectric. Since the structure of these first layers may significantly differ from
that of the bulk, the determination of the molecular orientation and packing of organic molecules at
the substrate interface is a crucial input for modeling the electronic band structure and the
associated charge-transport properties.
For this reason we have studied in-situ and in real time, during the UHV deposition of PDI-8CN2
molecules, the i) the growth dynamics (layer by layer or 3D), ii) the molecular packing, the
microstructure of the organic film and iii) the electrical properties of the OFET.
The structural study was achieved by performing Grazing Incidence X-ray Diffraction (GIXD) and
X-Ray Reflectivity (XRR) measurements. The electrical measurements were performed on FET
structures by collecting the source-drain current during the semiconductor deposition.
Thanks to these time-resolved measurements we could describe the thin-film growth dynamics the
influence of the substrate temperature, the deposition flux and the relation between the charge
transport properties and the growth mechanism of the thin film. In particular, we have have
observed that by tuning the substrate temperature we can improve the crystallinity of the PDI8CN2
thin film and modify its growth mode in order to increase the charge transport mobility and,
therefore, optimize the OFET performance.
Acknowledgements
We wish to acknowledge Dr. Roberto Nervo and Dr. Oleg Konovalov for their excellent support
during the experiment performed at ESRF and Dr. Silke Koehler (BASF Schweiz AG) for material
supply and fruitful discussions.
References
[1] B Yoo, et al. Appl. Phys. Let. 88, 082104 (2006)
[2] BA Jones, et al, Adv. Funct. Mater.18, 1329 (2008)
[3] J. Rivnay et al Nature Material 8 952 (2009)
102
Modelling morphology and electronic properties of hybrid ZnO - oligothiophene
nanostructures
G. Malloci1,*, C. Caddeo2, M. I. Saba1, C. Melis2, L. Colombo2, A. Mattoni1
1
Istituto Officina dei Materiali del CNR, Unità di Cagliari
Dipartimento di Fisica Universita' degli studi di Cagliari
*Cittadella Universitaria, S.P. Monserrato-Sestu Km 0.700
I-09042 Monserrato (CA) - ITALY
2
Tel: +39 070 675 4843
Fax: +39 070 510171
[email protected]
Hybrid systems made of conjugated organic molecules and inorganic semiconductors are attracting
great interest in recent years since they combine the favorable features of both components in a
single new material [1]. Driven mainly by photovoltaic applications, much attention has been paid
to the link between organic oligomers and polymers with zinc oxide surfaces [2]. Accurate
characterization of these interfaces remains an open issue due to the diffïculty in measuring
properties across a single junction at the nanometric and sub-nanometric scale. This challenge
makes atomistic simulations an important tool for understanding and predicting the interfacial
morphology and electronic properties. Here, we perform a combined model potential molecular
dynamics plus density functional theory study on hybrid systems composed by oligothiophene
derivatives adsorbed on ZnO nanostructures [3]. We investigate the energetics of adhesion and the
morphological features as well as the energy level alignment at the interface [4]. In particular, the
energy-level alignment for sexithiophene on the ZnO curved nanoparticle does not lead to a type-II
junction with staggered band gaps, contrary to what was recently found for sexithiophene on a flat
(1010)
̅ ZnO surface [5].
This work is funded by the Italian Institute of Technology (IIT) under Seed Project
"POLYPHEMO" and Regione Autonoma della Sardegna under L.R.7/2007.
[1] C. Sanchez, K. J. Shea, S. Kitagawa, Chem. Soc. Rev. 40, 471 (2011)
[2] S. Dag and L.-W. Wang, Nano Lett. 8, 4185 (2008)
M. I. Saba, C. Melis, L. Colombo, G. Malloci, A. Mattoni, J. Phys. Chem. C 115, 9651 (2011)
[3] G. Malloci, L. Chiodo, A. Rubio, A. Mattoni, J. Phys. Chem. C 116, 8741 (2012)
[4] C. Caddeo, G. Malloci, G.-M. Rignanese, L. Colombo, A. Mattoni, J. Phys. Chem. C 116, 8174
(2012)
[5] S. Blumstengel et al. Appl. Phys. Lett. 92, 193303 (2008)
N. Sai, K. Leung, J. R. Chelikowsky, Phys. Rev. B 83, 121309 (2011)
103
Role and treatment of Van der Waals forces at the C6H6/Ag(111) interface
D. Forrer* 1,4, M. Pavone 2, A. Vittadini1, V. Barone3, M. Casarin4,1
1
ISTM – CNR; Padova
2
Dipartimento di Chimica “Paolo Corradini” – Università “Federico II” di Napoli
3
Scuola Normale Superiore; Pisa
4
Dipartimento di Scienze Chimiche – Università di Padova
Since the pioneering work of Zaremba and Kohn [1], it became evident that a proper description of
physisorption on metal surfaces must include dispersion interactions. In spite of this, metal/organic
interfaces are usually studied using approaches derived from the Density Functional Theory (DFT),
even if local and semilocal implementations of the exchange-correlation (xc) functional are known
to be unable to catch the essence of dispersion forces. In fact, many-body perturbation theory
(MBPT) and coupled cluster techniques are the methods of choice to obtain an accurate prediction
of van der Waals forces, but the huge computational demand of MPBT-derived approaches prevents
their application to large systems. The inclusion of dispersion forces within the framework of DFT
would be highly desirable, allowing the accurate prediction of a variety of chemical systems while
exploiting the computational effectiveness of the DFT codes. In the last decade, several methods to
overwhelm this deficiency have been proposed by different authors and successfully applied to the
study of van der Waals compexes and soft materials.
Unfortunately, when applied to the case of organic molecules adsorbed on metal surfaces, all these
methods give only moderate improvement with respect to the DFT picture. In particular, both the
DFT-D2 [2] and the DFT-D3 [3] approaches overestimate the dispersion interaction at the
metal/organic interface, while the vdw-DF [4] functional, provides better values for the adsorption
energy, but overestimates the metal-molecule distance.
Thanks to its simple functional form, the DFT-D2 scheme can be modified quite easely to fit
experimental and/or accurate computational results. Here, we report a reparameterization of the
DFT-D2, where the van der Waals radius of Ag was modified to fit MP2 data on a cluster model of
the Ag(111) surface decorated by a C6H6 molecule. Results on a periodic model of the Ag(111)
surface covered by one monolayer of C6H6 are then compared to other dispersion-corrected DFT
schemes as well as to experimental data. Finally, the modified parameter is successfully applied to
the study of the adsorption of metal-free phthalocyanine H2Pc on the same substrate.
1. E. Zaremba and W. Kohn, Phys. Rev. B, 1976, 13, 2270; E. Zaremba and W. Kohn, Phys. Rev.
B, 1977, 15, 1769.
2. S. Grimme, J. Comput. Chem., 27, 2006, 1787.
3. S. Grimme, J. Antony, S. Ehrlich and H. Krieg, J. Chem. Phys., 2010, 132, 154104.
4. M. Dion, H. Rydberg, E. Schröder, D. C. Langreth, and B. I. Lundqvist, Phys. Rev. Lett., 2004,
92, 246401.
* ISTM-CNR c/o Dipartimento di Scienze Chimiche, Università di Padova,Via Marzolo 1, 25131 Padova (PD). E-mail:
[email protected]
104
NEXAFS spectra of aromatic molecules by plane-wave calculations
Guido Fratesi and Gian Paolo Brivio
ETSF, CNISM and Dipartimento di Scienza dei Materiali, Università di Milano Bicocca, Italy
Near-edge x-ray absorption fine structure (NEXAFS) is a powerful technique which allows one to
determine several important properties of organic molecules, both in the gas phase and in the bulk
or adsorbed one. In particular, one has access to the LUMO/LUMO+1 molecular states and, by
performing angle-dependent measurements with polarized x-rays, to the absolute orientation of
molecules in condensed phases provided that measured peaks can be associated to specific
transitions. With the increasing interest in hybrid organic/inorganic interfaces for photovoltaics and
other electronic applications, it is hence relevant to investigate theoretically the NEXAFS spectrum
of molecules of enlarging complexity and the effect of molecule-substrate interactions on the
spectrum itself, in order to fully disclose the experimentally derived information.
To this respect, the use of numerically-efficient yet accurate first-principles simulations in
determining the spectral features is desirable, aiming at simulating fairly large systems such as
molecules interacting with metal/dielectric surfaces. In particular, a technique to derive effectively
the spectrum from density-functional theory, using pseudopotentials and plane wave basis sets,[1] is
available to the community since few years[2]. It is based on assuming static interactions between
the core hole and the excited electron (which is justified for deep shells as the 1s of C) and allows
one to compute the spectrum and its dependence on the photon polarization in a wide energy range,
starting from the LUMO peaks up to resonances in the continuum without having to actually
perform prohibitive summations over empty states. However, that was mostly applied to bulk
systems.
Here, the basic aspects to its applicability to molecular systems will be discussed, taking as
examples benzene and pentacene molecules and comparing to experimental and theoretical data in
the literature. Numerical and technical details will also be considered, trying to highlight the
capabilities and limitations of the method, as well as the effect of approximations taken. Some of
these aspects, such as the adoption of a full/half-core-hole approximation, will also be pointed out
by making reference to atomic systems, where “exact” results are available in this context.
[1] P. Giannozzi et al., J. Phys.:Condens. Matter 21 395502 (2009)
[2] M. Gougoussis, M. Calandra, A. P. Seitsonen, and F. Mauri, Phys. Rev. B 80, 075102 (2009)
Guido Fratesi: Dipartimento di Scienza dei Materiali dell'Università di Milano-Bicocca, via Cozzi 53, 20125 Milano.
Tel.: +39.02.6448.5183; Email: [email protected]
105
Predicting the alignment of liquid crystals at a solid surface: 5-cyanobiphenyl on
cristobalite and glassy silica surfaces of various roughness
Otello Maria Roscioni, Luca Muccioli, Raffaele Guido Della Valle,
Antonio Pizzirusso, Matteo Ricci, and Claudio Zannoni*
Dipartimento di Chimica Fisica e Inorganica, Università di Bologna,
viale Risorgimento 4, 40136 Bologna, Italy
We employ atomistic molecular dynamic simulations to predict the alignment and anchoring of a
typical nematic liquid crystal, 4-n-pentyl-4'-cyano biphenyl (5CB), on different forms of silica. In
particular we study a nano-thick (20 nm) film of 5CB supported on surfaces of cristobalite and
amorphous silica of different roughness. We find that the anchoring properties of the liquid crystal
are correlated with the morphology of the silica surface support and its roughness.
*Corresponding author: Prof. Claudio Zannoni, Dipartimento di Chimica Fisica e Inorganica, Università di Bologna,
viale Risorgimento 4 IT-40136 Bologna, Italy. Email: [email protected]
106
Organic semiconducting single crystals as next generation of low cost, room
temperature electrical X-ray detectors
By B.Fraboni1*, A.Ciavatti1, L.Pasquini1,A.Cavallini1 A Quaranta2 A.Bonfiglio3 and A.FraleoniMorgera4
1
Università di Bologna - Dipartimento di Fisica, viale Berti Pichat 6/2, 40127 Bologna, Italy
[email protected]
2
Università di Trento – Dipartimento Ingegneria dei Materiali e Tecnologie Industriali – DIMTI,
Via Mesiano 77, 38050 Povo, Trento, Italy
3
Università di Cagliari – Dipartimento Ingegneria Elettrica, Piazza d’Armi, Cagliari, Italy
4
Sincrotrone Trieste – Strada Statale 14, Km 163.5 – Basovizza (Trieste), 34012 Italy
Ionizing radiation can be detected by directly converting it into an electrical signal. Only few and
expensive inorganic semiconductors (e.g. CdTe, SiC) offer the possibility of realizing portable
detectors that operate at room temperature. Organic semiconductors are very promising materials
for several different electronic applications, spanning from thin film transistors (TFT), to light
emitting diodes (LED), to solar cells and sensors. As detectors for ionizing radiation, organic
semiconductors have been so far mainly proposed in the indirect conversion approach, i.e. as
scintillators, which convert ionizing radiation into visible photons, or as photodiodes, which detect
visible photons coming from a scintillator and convert them into an electrical signal. The direct
conversion of ionizing radiation into an electrical signal within the same device is a more effective
process than the indirect one, since it improves the signal-to-noise ratio and it reduces the device
response time. We report here the use of organic semiconducting single crystals (OSSCs) as
intrinsic direct ionizing radiation detectors, thanks to their stability, good transport properties and
large interaction volume. X-ray detectors, based on low-cost solution-grown OSSCs are here shown
to operate at room temperature, providing a stable linear response with increasing dose rate in
atmosphere and in radiation-hard environments. The intrinsic conversion of X-rays within the
crystals allowed to fabricate all-organic optically transparent devices, indicating OSSCs as very
promising candidates for a novel generation of low-cost, room temperature, portable X-ray
detectors.
107
Investigations on the response of organic semiconducting single crystals to
polarized IR spectroscopy under charge polarization and flow
A. Fraleoni-Morgera1, E. Capria, L. Benevoli, B. Fraboni2, M. Tessarolo2, L. Baldassarre1,
A. Perucchi1, S. Lupi1,3
1
Sincrotrone Trieste, SS. 14 Km 163.5, 34149 Basovizza, Trieste, Italy
[email protected]
2
Dept. of Physics, Univ. of Bologna, V. Berti Pichat 6/2 - 40127 Bologna, Italy
3
Dept. of Physics, Univ. of Roma “La Sapienza”, Piazzale Aldo Moro 2, 00185 Roma, Italy
Organic semiconducting single crystals (OSSCs) are currently regarded as model systems for
investigating transport in organic semiconductors, due to their structural order. Solution-grown
single crystals based on the intrinsically polar 4-hydroxycyanobenzene (4HCB) molecule evidenced
reproducible, three-dimensional anisotropic electronic properties, such as carrier mobilities, density
of states distribution, deep traps concentration and energy levels. Accurate linearly polarized IR
(LP-IR) studies of 4HCB crystals unveiled further interesting optical properties, like 2D spectral
anisotropy (which allows to identify reproducibly and beyond any doubt the crystal axes with no
need for X-ray or electrical measurements), 2D anisotropic hydrogen bonding degree, and a 3D
anisotropic rotation of the electric dipole vector upon electrical polarization of the crystal. In
addition, when the crystals are probed in an OFET structure under actual charge transport flow, a
2D anisotropic IR screening effect of the charge transport layer is detected. The above mentioned
results will be presented and discussed in the relation to the elucidated crystal structure [2], together
with novel LP-IR investigations on 4HCB crystals under actual current flow (in an OFET
configuration), at temperatures down to 140 K.
Refs
[1] B. Fraboni et al., Adv. Mater. 21, 1835 (2009); Org. Electron., 11, 10 (2010)
[2] A. Fraleoni-Morgera et al., J. Phys. Chem. C, in press
108
Author
index
Acres R. G. 46, 101
Affronte M. 65
Alberti A. 79
Albonetti C. 96, 102
Alessandrini A. 81
Alfè M. 20
Alfieri R. 91
Alippi P. 12, 69
Ambrosio A. 67, 92
Amore Bonapasta A. 12, 58,69
Anghinolfi L. 64
Annese E. 26, 63
Arima V. 11
Arnaud G. F. 47
Attolini G. 29
Aversa L. 29,74,89
Baldassarre L. 108
Barborini E. 95
Barone V. 104
Barra M. 20,31,48,66,84,89,90
Batra A. 13
Bavdek G. 24
Bellingeri E. 54, 64
Bellini V. 65
Beltram F. 18
Benassi E. 83
Benevoli L. 108
Benwadih M. 33
Bergenti I. 97
Berzina T. 27,49
Betti M.G. 94
Bettotti P. 66,88
Beverina L. 14
Biscarini F. 30,96,102
Bisio F. 64,95
Bisti F. 50, 67
Blankenburg S 39
Bloisi F. 20
Blond H. 53
Bobba F. 51
Bondino F. 39,52
Bonfiglio A. 107
Bonucci A. 68
Borbone F. 92
Borga E. 53
Borgatti F. 96
Borghetti P. 78
Bortolotti C.A. 96
Bramanti A.P. 11
Brancolini G. 62
Brivio G. P. 105
Broch K. A. 102
Bruno A. 56
Buzio R. 54,64
Caddeo C. 21,103
Caldas M. J. 36
Calestani D. 93
Calzolari A. 22,55,77,78,94
Camposeo A. 80,92
Canepa M. 71,95
Capelli R. 35
Capogrosso V. 52
Caporali S. 101
Capria E. 108
Carallo S. 70
Carella A. 84
Carofiglio T. 28
Casalini S. 96
Casarin M. 28,74,104
Casolari F. 26
Cassinese A. 20,23,31,48,56,66,84,89,90
Castellarin-Cudia C. 39,78
Cataudella V. 15, 75
Catellani A. 22,55
Causà M. 84
Cavalleri O. 95
Cavallini A. 107
Centore R. 84
Cháb V. 46
Chelli B. 30
Chen Z. 48,98
Chen, Z. 48
Chiarella F. 20,31
Ciavatti A. 107
Ciccullo F. 23,48,56,84,89
Cocchi C. 36
Coletti C. 18
Colle R. 57
Colombo L. 21,103
Colonna, S. 58
Condorelli G. G. 79
Contini G. 19
Coppard R. 33
Coppedè N. 91, 93
Corni S. 59, 83, 85
Corradi C. 53
Corradini V. 65
Cossaro A. 39,60,76
Costa D. 37
Cozzoli D. 38
Cramer T. 30
Cricenti A. 58
Cristofolini L. 29
Cucolo, A.M. 51
Cvetko D. 13
Cvetko D. 60
D’Avino G. 99,100
D’Ischia M. 82
Daami A. 33
Dal Zilio S. 86
Daniel C. 51
De Girolamo A. 68
De Marco P. 67
De Renzi V. 47
De Stefano L. 61
Dediu V. A. 97
Del Mauro 68
Del Pennino U. 47,65
Della Sala F. 87
Della Valle R. G. 106
Destri S. 96
Di Capua R. 90
Di Felice R. 62,85
Di Giovannantonio M. 19
Di Girolamo F.V. 31,48,90,98
Di Marino M. 28
Di Santo G. 39,78
Donarelli M. 50
Draxl C. 25
Eguchi R. 34
El Garah M. 19
Erokhin V. 27,49
Esaulov V. 71
Fabbri F. 29
Fabiano E. 87
Fabris S. 94
Facchetti A. 17,35,48,98
Facci P. 81
Fanetti M. 39
Farinola G. 96
Fasoli C. 53
Fasolino T. 68
Felici R. 77
Ferdeghini C. 54
Feyer V. 46
Filippone F. 12,58,69
Fioriti F. 67
Floreano L. 13, 24,39,60
Fölsch S. 72
Forrer D. 104
Fortuna S. 94
Fortunato G. 33
Fraboni B. 107,108
Fraleoni Morgera A. 76
Fraleoni-Morgera A. 107,108
Frassetto F. 73
Fratesi G. 105
Fujii J. 26,63
Fujii, J. 63
Gadaleta A. 64
Gargiani P. 94
Genco A. 70
Gerbi A. 54,64
Ghane, T. 62
Ghirri A. 65
Giannozzi P. 69
Giardina P. 61
Gigli G. 38,70
Giglia A 71, 73
Goldoni A. 39,78
Goler S. 18
Goto H. 34
Gottardi S. 66,88
Graziosi P. 97
Grill L. 10
Grosso G. 57
Guerra G. 51
Gutiérrez Lezama I. 48,98
Hamao S. 34
Haque S.A. 56
He X. 34
Heun S. 18
Iakhnenko M. 46, 101
Iannotta S. 29,53,66,74,88,89,91,93
Jacob S. 33
Kambe T. 34
Kanisawa K. 72
Karmakar S. 11
Kawai N. 34
Kawale S. 54
Kladnik G. 13,60
Komura N. 34
Kowarik S. 102
Kubozono Y. 34,66
Kumar M. 77,78
Lanzilotto V. 12,24
Lazzarini L. 93
Leonardi F. 96
Lettieri S. 23,31,67
Lipton-Duffin J. A. 19
Liscio A. 16
Liscio F. 102
Loiudice A. 38
Longobardi, S. 61
Lubian E. 28
Lupi S. 108
M. Sassi M. 14
Maddalena P . 23,67,92
Maglione, M. G. 68
Magnano E. 39,52
Mahne N. 71
Malloci G. 21,69,103
Malvestuto, M. 52
Manca L. 82
Maniglio D. 53
Mariani F. 29,94
Mariano F. 70
Marigliano Ramaglia V. 15,75
Mariucci L. 33
Marré D. 54, 64
Martin-Samos L. 57
Maruccio G. 11
Mashoff T. 18
Matolín V. 46
Mattioli G. 12,58,69
Mattoni A. 21,69,103
Mazzei L. 23
Mazzeo M. 70
Meinardi F. 14
Meisner J. S. 13
Melis C. 21,69,103
Melucci M. 16
Milita S. 102
Minarini C. 68
Minati L. 53
Minder N. 48, 98
Molinari .E. 36
Monguzzi A. 14
Morgante A. 12,13,39,60
Morpurgo A. 48, 98
Mosca R. 91,93
Muccini M. 35
Muccioli L. 99,100,106
Mukherjee S. 71,73
Mula G. 82
Muniz-Miranda M. 101
Murgia M. 30
Nacci C. 72
Nakano M. 98
Nannaarone S. 71,73,74
Nardi M. 29,74,93
Nasi L. 29
Nenna G. 68
Nobile G. 68
Nocera A. 15, 75
Nuckolls C. 13
Olivieri G. 76
Omar O.H. 96
Operamolla A. 96
Ottaviano L. 50, 67
Pagani G. A. 14
Pagliai M. 101
Palenzona A. 54
Palermo V 16.
Paltrinieri L. 96
Panaccione G. 26
Pandolfi G. 68
Paoletti A.M. 12, 58
Parmigiani F. 52
Pasini M.C. 96
Pasquali L. 71,73,107
Passacantando M. 67
Passerone D. 39
Pavone M. 104
Pedio M. 77,78,101
Pellegrini V. 18
Pellegrino G. 79
Pennesi G. 12, 58
Perroni C.A. 15,75
Persano L. 80
Perucchi A. 108
Petrangolini P. 81
Petronini P. 91
Pezzella A. 20,82
Picozzi S. 50
Pignedoli C. A. 39
Pipolo S. 83
Pisignano D. 80,92
Pizzirusso A. 106
Plekan O. 46
Pola M. 53
Poletto L. 73
Porzio W. 96
Pratesi G. 101
Prezioso M. 97
Prezioso S. 67
Prezzi D. 36
Primiceri E. 11
Prince K. C. 46,101
Quaranta A. 107
Quiroga S. D. 102
Radivo A. 86
Rapisarda M. 33
Rea I. 61
Resta A. 77
Ricci M. 106
Ricciotti L. 66,84
Rigo E. 88
Riminucci A. 97
Rimoldi T. 29
Rinaldi R. 11
Rizzo A. 38
Rocca M. 37
Romeo A. 91
Ronci F. 58
Rosa M. 85
Roscioni O. M. 106
Rosei F. 19
Rossi F. 29
Rossi G. 12,26,58,63
Roviello A. 84,92
Rufolo, C. 51
Ruini A. 22,36
Saba M. I. 21,103
Salluzzo M. 31
Salviati G. 29
Sambi M. 28
Sanguineti A. 14
Santoro F. 90
Santucci S. 67
Savio L. 37
Scarfato A. 51
Schettino V. 101
Schlierf A. 16
Schreiber F. 32,102
Sedona F. 28
Setzu S. 82
Sfligoj C. 39
Shehu A. 96,102
Siri A. S. 54,64
Siwko M. E. 59
Skála T. 46
Smerieri M. 37
Sovernigo E. 86
Stebel L. 52
Stroppa A. 50
Taglialatela M. 90
Tarabella, G. 91
Tassini P. 68
Terentjevs A. 87
Terzi F. 71
Tessarolo M. 108
Tielens F. 37
Timco G. 65
Toccafondi C. 95
Toccoli T. 53,66,88
Toffanin S. 35
Tonezzer M. 88
Tormen M. 86
Tozzini V. 18
Tranca I. 37
Treossi E. 16
Tsud N. 46,101
Tubino R. 14
Umari, P. 78
Vaccaro G. 14
Valletta A. 33
Varsano D. 62
Vattuone L. 37
Vazquez H 13
Venkataraman L. 13
Verdini A. 12,39,60
Verucchi R. 29,74,89
Vicari L. 20
Viggiano D. 90
Vignali F. 96
Villani M. 93
Vittadini A. 74
Vittadini A. 104
Vobornik I. 26,63
Winpenny R. 65
Xia Z. Y. 16
Yabloskikh M. 52
Zamboni R. 35
Zannoni C. 99,100,106
Zappettini A. 93