Electron and ion stimulated desorption of positive ions from SF6 adsorbed on a Ta surface

Abstract

The mechanism of secondary ion emission has been investigated by electron and He+ ion irradiation of the SF6 layer formed on a polycrystalline Ta substrate. Quite similar results are obtained between electron and He+ excitations; the fragment ions (SFx+, x=0–5) are emitted intensively from multilayers but they are absent when adsorbed directly on Ta due to delocalization of the valence hole(s). The F+ yield, though very small from the physisorbed SF6 layer, is increased by more than ten times after heating or irradiation with the electron or He+ beam, indicating that F+ arises from the chemisorbed F adatoms much more intensively than from the physisorbed SF6 molecule. This is because the F+ ion is not initiated by the valence holes state but arises from the screened F 2s core–hole state followed by the intra-atomic Auger decay after breakage of the chemisorptive bond, thereby avoiding efficient resonance neutralization on the metal surface.