Molecular activation on hotsurfaces by first principles
G Tabacchi*, E Fois, D.Barreca, A . Gasparotto, E. Tondello
Congresso Nazionale
di Chimica Fisica 2010
STRESA 20-24/09/2010
gloria tabacchi
insubria university - Como
[email protected]
http://scienze-como.uninsubria.it/gloria
Molecules @ hot surfaces:
……may
lead to
organized
nanostructures
ac
(not achievable at mild
conditions)
…through
alternative and
unexpected
pathways
For example, on MgO at T≈400 K..e
Ru3 + Os3 clusters
Ru–Os clusters
A. Kulkarni, B. C. Gates, Angew. Chem. Int. Ed. 2009, 48, 9697.
to get Ru-Os, desorption and migration of Os3/Ru3
clusters must take place. How?
The Chemical Vapor Deposition (CVD) process
M
Co
Few nm
CVD
O2
Molecular
precursor
Co(hfa)
2●TMEDA
Cobalt
oxides
Metal
oxides
CuxO (x=1,2)
nanosystems
CuII precursor
HEATED
SUBSTRATE
CuII
Continuous films
N
O1
Quasi-1D
nanosystems
CVD
O2
T=523-823K
Gas sensing
Cu (hfa)2 tmeda
(Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate;
TMEDA = N,N,N’,N’-tetramethyl-ethylendiamine)
Ts[Cu(hfa)2(TMEDA)] = 343 K
A PCCP 2009, 11, 5998
H2
production
400°C
400°C
From Cu2O
granular films…
200 nm
100 nm
450°C
450°C
dry O2
atmosphere
200 nm
100 nm
500°C
200 nm
500°C
100 nm
550°C
550°C
200 nm
1 μm
…to CuO 1D
nanoarchitectures
(NWs)
Cryst. Growth Des. 2009, 9, 2470
By CVD processes /advanced experimental techniques…
we can:
we can not:
• grow nanostructures from
molecular precursors
• know how molecules are
converted into materials:
• control their phase
composition and
morphology
• Precursor Activation on
the heated substrate
• Precursor decomposition
• exploit their functional
properties
(liberation of the metal centre
through ligand elimination)
• MOx formation mechanism
This work
Modeling the first stages of the CVD process:
activation of the Cu(hfa)2TMEDA precursor
on a hot substrate (T = 750 K)
 Substrate surface @
CVD-conditions:
hydroxylated SiO2
 Model surface:
1 nm thick SiO2 slab with
2.8 Si-OH groups /nm2
Problem:
the Cu center
is protected
by the
ligands!
Physisorption, rolling diffusion & molecular
activation
Three different regimes:
a) Slow diffusion; b) physisorption; c) fast diffusion by rolling
in-plane (x,y) trajectory
Å
b
Å
Mean square displacement
30 ps first principles molecular dynamics simulation
of the Complex/Surface system at T=750 K
Key role of the surface/molecule energy transfer
in the complex activation
Physisorption:
Fast Rolling diffusion:
Close contacts with the
hot surface favor energy
transfer to the molecule
 @ 750 K, kT/hc = 550 cm-1
 Cu-Ligand bond stretching
frequencies < 600 cm-1
Large deformations
interligand interactions
..A vibrationally excited
complex rolling on a hot
surface may do this…
Or this:
…..Or ?
… and then?
conclusions
Fast rolling diffusion regime:
Stems from surface-molecule energy transfer
 Triggers molecular activation
May be a general feature of high temperature
surface chemistry
A novel phenomenon,
many open questions ….
Acknowledgements
• MIUR PRIN 2007 project “ Microscopic features of
chemical reactivity”
• CNR-INSTM PROMO
• CARIPARO Foundation within the project “Multi-layer
optical devices based on inorganic and hybrid materials
by innovative synthetic strategies”
Perspectives??
Work in progress
Grazie per l’attenzione
Cu2O
O2 + H2O
atmosphere
CuO
vibrational spectra of the isolated Cu(hfa)2 tmeda complex
experimental
calculated
Main peaks assignment (cm-1):
2800-3300: (C-H); 1674: (C=O); 1400-1560: (C=C), (C-H) + (CH3)/(CH2)
1140-1260: combination of (C-H), (C-CF3), (C-F)
576: (Cu-Oeq.); 319 (Cu-Oap.); 490: (Cu-N)
U-B3LYP/Cu: ECP10-MDF/aug-cc-pVDZ-PP; Ligands: D95+* level of computation
G. Bandoli et al. PCCP, 2009, 11, 5998.