Secondary-ion emission from oxygen and hydrogen-covered beryllium surfaces: I. Coverage dependence

Secondary ion emission from a beryllium surface is studied in the presence of hydrogen and oxygen. For submonolayer coverages of oxygen, the adsorption follows site-exclusion statistics. On this basis, the Be⁺ secondary ion yield and energy distribution can be separated into oxygen-dependent and oxygen-independent processes governed by the local properties of the surface. Ionic molecular species with hydrogen or oxygen present include Be₂O⁺, Be₂O^?, BeO^?, and BeH⁺ but not BeO⁺ or BeOH⁺. This result is inconsistent with emission in which the oxide molecule is formed in the near-surface vacuum region by agglomeration of individually sputtered surface atoms. For BeH⁺emission the opposite conclusion is reached.