33rd International Field Emission Symposium / 33ème Symposium International d'Emission de Champ

J. Phys. Colloques 47 (1986) C7-343-C7-348
DOI: 10.1051/jphyscol:1986759

FIELD-ASSISTED PHOTODESORPTION OF IONS FROM METAL AND SEMICONDUCTOR SURFACES

S. JAENICKE¹, A. CISZEWSKI², W. DRACHSEL¹, U. WEIGMANN³, T.T. TSONG⁴, J.R. PITTS⁵, J. H. BLOCK¹ et D. MENZEL<sup>6

1</sup>  Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-1000 Berlin 33, F.R.G.
²  On leave from Physical Department, University of Wroclaw, PL 50-205 Wroclaw, Poland
³  Fraunhofer Institute for Microstructure Research, D-1000 Berlin 33, F.R.G.
⁴  On sabbaticel leave from Physics Department, Pennsylvania State University, University Park, PA 16802, U.S.A.
⁵  Solar Energy Research Institute, Golden, CO., U.S.A.
⁶  Physics Department, Technical University of Munich, D-8046 Garching, F.R.G.

Abstract
The influence of strong electric fields on the photon-stimulated desorption of small molecules from metal and silicon surfaces has been studied. With hydrogen only field adsorbed H₂ as well as H₃ are desorbed as singly charged ions. Chemisorbed atomic hydrogen obviously has a photo-ionization cross-section at metal surfaces which is too small to be detected. From clean and oxidized Si surfaces H⁺ as well as Si-containing hydrides and oxides are photodesorbed at field strengths as low as 6V/nm. Field adsorption of water leads to whisker-like layers, from which H₃O⁺·nH₂O-clusters are photo-desorbed with rather high quantum yields. The desorption spectrum exhibits a sharp onset at a wave length of 165 nm ; the onset energy shifts with decreasing field strength towards higher energies.