Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

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JUNE 28 WEDNESDAY MORNING RIVA-SS-WeM-OR.4 DESIGN OF AN ELECTROSTATIC LENS SYSTEM FOR AN ULTRAVIOLET PHOTOELECTRON SPECTROMETER. R. M. Pinto 1,2 , A. A. Dias 1,2 and M. L. Costa 1,2 . 1 Centre for Physics and Technological Research, CEFITEC, 2 Departamento Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Monte de Caparica, 2829-516, Caparica, Portugal e-mail: aad@fct.unl.pt The control of an electron beam plays an important role in most of the electron spectrometer systems, nowadays. Although the use of electrostatic lenses, for purposes of focusing the particles, is not always necessary, the overall quality of the system in which they are inserted can be improved. This work aims to design an electrostatic lens system [i] that improves the resolution at the entrance of a hemispherical deflection analyzer, of a working ultraviolet photoelectron spectrometer [ii,iii], while maintaining a constant transmission. The spectrometer does not have any kind of controlled focusing device other than a spatial collimator. An optimal solution has to be found, concerning the dimensions of the existing apparatus. Simulations using ion optics programs and the study of several lenses configurations are the suitable means to reach such a goal. The existence of aberrations is taken into account. References [i] O. Sise, M. Ulu, M. Dogan. Nucl. Instr. and Meth. in Phys. Res. A 2005, 554, 114-131. [ii] J.M. Dyke, G. Levita, A. Morris, J.S. Ogden, A.A. Dias, M. Algarra, J.P. Santos, M.L. Costa, P. Rodrigues, M. Andrade, M.T. Barros. Chem. Eur. J. 2005, 11, 1665-1676. [iii] L. Beeching, A.A. Dias, J.M. Dyke, A. Morris, S. Stranges, J. West, N. Zema, L. Zuin, Molecular Physics 2003, 101, 575-582. 92
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
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Sigilum Universitatis Studii Salama
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