Field-assisted photodesorption of ions from metal and semiconductor surfaces

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