Formation of mixed layers and compounds on beryllium due to C+ and CO+ bombardment

Compound formation on a clean beryllium single crystal (0 0 0 1) during bombardment with 5 keV C+ and 3 and 5 keV CO+ ions is studied by means of in situ X-ray photoelectron spectroscopy (XPS). In combination with in situ Rutherford backscattering analysis (RBS), TRIDYN computer simulation, and measurements of the weight change of the sample due to the bombardment, models for the sample composition changes and erosion mechanisms are derived for both ion species. In the case of C+ bombardment a carbon layer builds up on top of the beryllium. The transition region from pure beryllium to pure carbon consists partly of Be2C and the beryllium erosion stops as the covering carbon layer develops. During CO+ bombardment a deposition/erosion equilibrium is established. After initial C and O accumulation, the beryllium substrate is covered by a ternary mixture layer of about 10 nm thickness containing BeO, elementary carbon and C–O compounds. Be2C is present only at low fluences and before the equilibrium is established. The erosion of beryllium proceeds and a chemical erosion process limits the deposited amounts of carbon and oxygen via emission of CO.