Molecular activation on hot-surfaces by first principles

1. G Tabacchi*, E Fois, D.Barreca, A . Gasparotto, E. Tondello Molecular activation on hot-surfaces by first principles gloria tabacchi insubriauniversity - Como gloria@fis.unico.it http://scienze-como.uninsubria.it/gloria Congresso Nazionale di Chimica Fisica 2010 STRESA 20-24/09/2010

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

3. 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. togetRu-Os, desorption and migrationof Os3/Ru3clustersmust take place. How?

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

5. CuxO (x=1,2) nanosystems Continuousfilms CuIIprecursor HEATED SUBSTRATE N CuII Quasi-1D nanosystems O1 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 H2 production A PCCP2009, 11, 5998

6. 450°C 450°C 100 nm 200 nm 550°C 550°C …toCuO 1D nanoarchitectures (NWs) 1 μm 200 nm From Cu2O granular films… 400°C 400°C 200 nm 100 nm dry O2 atmosphere 500°C 500°C 200 nm 100 nm Cryst. Growth Des.2009, 9, 2470

7. By CVD processes /advancedexperimentaltechniques… we can: 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) MOx formation mechanism • grownanostructuresfrommolecularprecursors • controltheirphasecomposition and morphology • exploit theirfunctionalproperties

8. 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!

9. Physisorption, rolling diffusion & molecular activation Three different regimes: a) Slow diffusion;b) physisorption;c) fast diffusion by rolling Mean square displacement in-plane (x,y) trajectory b Å Å

10. 30 ps first principles molecular dynamics simulation of the Complex/Surface system at T=750 K • Substrate surface @ CVD-conditions: hydroxylated SiO2 • Model surface: 1 nm thick SiO2 slab with 2.8 Si-OH groups /nm2

11. Key role of the surface/molecule energy transfer in the complex activation Physisorption: Close contacts with the hot surface favor energy transfer to the molecule • Fast Rolling diffusion: • Largedeformations • interligandinteractions • @ 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 l’attenzione

19. Cu2O O2 + H2O atmosphere CuO

20. 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. Bandoliet al. PCCP, 2009, 11, 5998. vibrational spectra of the isolated Cu(hfa)2 tmeda complex