Presentation on theme: "Molecular activation on hot- surfaces by first principles gloria tabacchi insubria university - Como"— Presentation transcript:
Molecular activation on hot- surfaces by first principles gloria tabacchi insubria university - Como firstname.lastname@example.org http://scienze-como.uninsubria.it/gloria G Tabacchi*, E Fois, D.Barreca, A. Gasparotto, E. Tondello Congresso Nazionale di Chimica Fisica 2010 STRESA 20-24/09/2010
ac Molecules @ hot surfaces: …… may lead to organized nanostructures (not achievable at mild conditions) …through alternative and unexpected pathways
For example, on MgO at T400 K..e Ru 3 + Os 3 clusters Ru–Os clusters to get Ru-Os, desorption and migration of Os 3 /Ru 3 clusters must take place. How? A. Kulkarni, B. C. Gates, Angew. Chem. Int. Ed. 2009, 48, 9697.
The Chemical Vapor Deposition (CVD) process Molecular precursor Metal oxides M
T s [Cu(hfa) 2 (TMEDA)] = 343 K Cu x O (x=1,2) nanosystems A PCCP 2009, 11, 5998 Quasi-1Dnanosystems CVD Continuous films (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N,N-tetramethyl-ethylendiamine) Cu (hfa) 2 tmeda O1 Cu II N O2 Cu II precursor HEATED SUBSTRATE Gas sensing T=523-823K H 2 production
By CVD processes /advanced experimental techniques… we can: grow nanostructures from molecular precursors control their phase composition and morphology exploit their functional properties we can not: know how molecules are converted into materials: Precursor Activation on the heated substrate Precursor decomposition (liberation of the metal centre through ligand elimination) MO x formation mechanism
Modeling the first stages of the CVD process: activation of the Cu(hfa) 2 TMEDA precursor on a hot substrate (T = 750 K) This work Problem: the Cu center is protected by the ligands! hydroxylated SiO 2 Substrate surface @ CVD-conditions: hydroxylated SiO 2 Model surface: 1 nm thick SiO 2 slab with 2.8 Si-OH groups /nm 2 Model surface: 1 nm thick SiO 2 slab with 2.8 Si-OH groups /nm 2
Physisorption, rolling diffusion & molecular activation Three different regimes: fast diffusion by rolling a) Slow diffusion; b) physisorption; c) fast diffusion by rolling Mean square displacement Å Å in-plane (x,y) trajectory b
30 ps first principles molecular dynamics simulation of the Complex/Surface system at T=750 K Substrate surface @ CVD- conditions: hydroxylated SiO 2 Model surface: 1 nm thick SiO 2 slab with 2.8 Si-OH groups /nm 2 Model surface: 1 nm thick SiO 2 slab with 2.8 Si-OH groups /nm 2
Physisorption: Close contacts with the hot surface favor energy transfer to the molecule Fast Rolling diffusion: Large deformations interligand interactions Key role of the surface/molecule energy transfer in the complex activation @ 750 K, kT/hc = 550 cm -1 Cu-Ligand bond stretching frequencies < 600 cm -1
..A vibrationally excited complex rolling on a hot surface may do this…
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