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JUNE 28 WEDNESDAY MORNING
RIVA-SS-WeM-OR.3 WORK FUNCTION CHANGES INDUCED BY TEMPERATURE
IN Ag/TiO 2 SURFACES. H. P. Marques, A. R. Canário, A. M. C. Moutinho and O. M. N. D.
Teodoro CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade
Nova de Lisboa, 2829-516 CAPARICA, Portugal
When one studies the catalytic behaviour of a surface, the energy required to remove electrons from
the surface is a meaningful parameter since electron transfer is involved in many surface reactions.
Therefore, the surface work function is important to understand the mechanisms of heterogeneous
catalysis.
Growth dynamics of silver clusters supported on TiO 2 (110) mono-crystals have been studied by
several authors [1-5]. Silver atoms deposited in the crystal at room temperature exhibit a 3D Volmer-
Weber growth mode. When the substrate is cooled to LN 2 temperature, the Ag atoms have very low
surface mobility and a quasi-2D growth is observed [2].
The work function measurements performed during cluster growth show different behaviour depending
on the substrate temperature, which translates on the cluster size [6]. During growth, at lower
temperature the WF changes more rapidly and tends to a lower value than at room temperature.
In this work we studied the work function as a function of the substrate temperature. One equivalent
monolayer of silver was deposited on a TiO 2 (110) surface at LN 2 temperature and a base value for
the work function was determined. The substrate was then annealed for 5 minutes. The sample was
allowed to cool down again to LN 2 temperature and the work function was measured. The procedure
was repeated for increasing annealing temperatures up to 200ºC.
For all work function measurements the onset method was used. The secondary electron threshold is
shifted in energy according to the work function change.
Keywords: Work function, titanium oxide, silver clusters.
[1] U. Diebold, Surface Science Reports, 48 (2003) 53.
[2] C.T. Campbell, Surf. Sc. Reports, 27(1997) 1 111
[3] C. Su, J.C. Yeh, J.L. Lin and J.-C. Lin, App. Surf. Sci. 169 (2001) 366.
[4] K. Luo, T.P. St Clair, X. Lai, and D.W. Goodman, J. of Phys. Chem. B 104 (2000) 3050.
[5] A.R. Canário, E.A. Sanchez, Yu. Bandurin and V.A. Esaulov, Surf. Sci. 547 (2003) L887
[6] H.P. Marques, A.R. Canário, O.M.N.D. Teodoro and A.M.C. Moutinho Riva V
proceedings, submitted to Vacuum
91