Angular dependence of secondary ion emission from silicon bombarded with inert gas ions

The emission of positive and negative, atomic and molecular secondary ions sputtered from silicon has been studied under ultrahigh vacuum conditions. The sample was bombarded with 2-12 keV Ar+ and Xe+ ions at angles of incidence between 00 and 600 to the surface normal. The angular dependence of the secondary ion intensity as well as the energy spectra of Si+ and Si- were found to differ significantly. The effect is attributed mostly do differences in the rate of neutralization. The stability of molecular ions appears to be independent of the charge state. Supporting evidence is provided for the idea that multiply charged secondary ions are due to Auger de-excitation of sputtered atoms in vacuum. (orig.)