Sputtering of Surfaces by Positive Ion Beams of Low Energy

Silver, germanium, and germanium-silicon alloy surfaces have been bombarded with the inert gas ions Ne+, A+, Kr+, and Xe+, at energies between 30 and 400 ev. Primary beam intensities between one and ten μa/cm2 were obtained in an oscillating electron source of the Heil type. The secondary particles sputtered off, neutrals as well as positive and negative ions, were identified and recorded in a 180° mass spectrometer of 5.5-inch radius. They are partly background gases adsorbed on the surface, partly atoms and molecules characteristic of the sample. Among the latter particles, neutrals were about 100 times more abundant than those emitted as positive ions. Rather low yields (about one sample atom per 100 incident ions with 400-ev energy) and relatively high threshold energies (40–50 ev for an angle of 30° between beam and surface) are believed to be due to surface contamination. Retarding potential measurements showed that over 80% of the particles sputtered have initial energies of less than 5 ev. After bombardment, the Ge and Ge-Si surfaces showed oval-shaped hillocks, possibly due to appreciable carbon concentrations in the samples studied. If the effects of surface contamination can be reduced, this method promises to be useful in the analysis of solid surfaces.