Molecular activation on hot-surfaces by first

principles

gloria tabacchigloria tabacchiinsubria university - Comoinsubria university - Como

gloria@fis.unico.ithttp://scienze-como.uninsubria.it/gloriahttp://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

acMolecules @ hot surfaces:

……may lead to organized

nanostructures(not achievable at mild conditions)

……through through alternative and alternative and

unexpected unexpected pathwayspathways

For example, on MgO at T≈400 K..e

Ru3 + Os3 clusters Ru–Os clusters

to get Ru-Os, desorption and migration of Os3/Ru3 clusters must take place. How?

A. Kulkarni, B. C. Gates, Angew. Chem. Int. Ed. 2009, 48, 9697.

The Chemical Vapor Deposition (CVD) process

CVD

O2

Co

Cobalt oxidesCo(hfa)2●TMEDA

Few nmCVD

O2

Co

Cobalt oxidesCo(hfa)2●TMEDA

Few nm

Molecular precursor Metal oxides

M

Ts[Cu(hfa)2(TMEDA)] = 343 K

CuCuxxO (O (xx=1,2) =1,2)

nanosystemsnanosystems

A PCCP 2009, 11, 5998

Quasi-1D Quasi-1D nanosystemsnanosystems

CVDCVD

Continuous filmsContinuous films

(Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N’,N’-tetramethyl-ethylendiamine)

Cu (hfa)2 tmeda

O1

CuII N

O2

CuCuIIII precursor precursor

HEATEDSUBSTRATE

Gas sensing

T=523-823K

H2

production

From CuFrom Cu22O O

granular films…granular films…

200 nm

400°C

100 nm

400°C

dry Odry O22

atmosphereatmosphere

200 nm

450°C

100 nm

450°C

200 nm

500°C

100 nm

500°C

……to CuO 1D to CuO 1D

nanoarchitecturesnanoarchitectures

(NWs)(NWs)200 nm

550°C

1 μm

550°C

Cryst. Growth Des. 2009, 9, 2470

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)

• MOx formation mechanism

Modeling the first stages of the CVD process:

activation of the Cu(hfa)2TMEDA precursor

on a hot substrate (T = 750 K)

This work

Problem:

the Cu center is protected

by the ligands!

Substrate surface @ CVD-conditions:

hydroxylated SiOhydroxylated SiO22

Model surface: Model surface: 1 nm thick SiO1 nm thick SiO2 2 slab with slab with 2.8 Si-OH groups /nm2.8 Si-OH groups /nm22

Physisorption, rolling diffusion & molecular activation

Three different regimes:a) Slow diffusion; b) physisorption; c) fast diffusion by rolling fast diffusion by rolling

Mean square displacement

Å

Å

in-plane (x,y) trajectoryb

30 ps first principles molecular dynamics simulation of the Complex/Surface system at T=750 K

Physisorption:Physisorption:

Close contacts with

the hot surface favor

energy transfer to the

molecule

Fast Rolling Fast Rolling

diffusiondiffusion::

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…

Or this:Or this:

……..Or ?..Or ?

… … and then?and then?

conclusionsFast 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

OO2 2 + H + H22OO

atmosphereatmosphere

CuOCuO

CuCu22OO

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. BandoliG. Bandoli et al. PCCP et al. PCCP, 2009, , 2009, 1111, 5998. , 5998.

experimental

calculated

experimental

calculated

vibrational spectra of the isolated Cu(hfa)2 tmeda complex