Simultaneous measurements of surface recombination velocity and added trapped charge density in the fast states as a function of surface potential were carried out on an w-type specimen which was subjected to the following gaseous ambient cycles: (a) room air-vacuum, (b) dry air-vacuum, (c) dry oxygen-vacuum, (d) dry nitrogen-vacuum, (e) wet nitrogen-vacuum, and (f) wet oxygen-vacuum. The most important results of these measurements were: (1) Dry nitrogen had no influence whatsoever on any of the surface-state parameters, (2) dry oxygen affected only the density of states and the unperturbed surface potential, and (3) wet nitrogen and wet oxygen had almost the same and most pronounced effect on the fast surface states.

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For a Ge(111) surface irradiated by an electron beam of 1.5-keV energy and current density of 2 μA mm−2, it was found that beam-assisted oxygen adsorption at pressures <10−9 Torr always resulted in carbon-contaminated overlayers and was probably due to dissociation of physisorbed CO. The sticking coefficient s of CO was 0.08. At oxygen pressures ≳10−6 Torr, carbon-free coverages could be formed, even without irradiation. s for oxygen was 6×10−4 for beam-assisted and 1.5×10−4 for nonassisted adsorption. Electron impact desorption followed a first-order rate equation and the desorption cross section for oxygen was 6×10−20 cm2.