1. Molecular activation on hot- surfaces by first principles gloria tabacchi insubria university - Como gloria@fis.unico.it 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

2. ac Molecules @ hot surfaces: …… may lead to organized nanostructures (not achievable at mild conditions) …through alternative and unexpected pathways

3. 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.

4. The Chemical Vapor Deposition (CVD) process Molecular precursor Metal oxides M

5. 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

6. From Cu 2 O granular films… 200 nm 400°C 100 nm 400°C dry O 2 atmosphere 200 nm 450°C 100 nm 450°C 200 nm 500°C 100 nm 500°C …to CuO 1D nanoarchitectures (NWs) 200 nm 550°C 1 μm 550°C Cryst. Growth Des. 2009, 9, 2470

7. 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

8. 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

9. 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

10. 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

11. 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

12. ..A vibrationally excited complex rolling on a hot surface may do this…

13. Or this: …..Or ? … and then?

14. 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 ….

15. 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

16. Perspectives??

17. Work in progress

18. Grazie per lattenzione

19. O 2 + H 2 O atmosphere CuO Cu 2 O

20. Main peaks assignment (cm -1 ): 2800-3300: (C-H); 1674: (C=O); 1400-1560: (C=C), (C-H) + (CH 3 )/ (CH 2 ) 1140-1260: combination of (C-H), (C-CF 3 ), (C-F) 576: (Cu-O eq. ); 319 (Cu-O ap. ); 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. vibrational spectra of the isolated Cu(hfa) 2 tmeda complex