An AES study of the room temperature conditioning of technological metal surfaces by electron irradiation

The modifications to technological copper and niobium surfaces induced by 2.5 keV electron irradiation have been investigated in the context of the conditioning process occurring in particle accelerator ultra high vacuum systems. Changes in the elemental surface composition have been found using Auger electron spectroscopy (AES) in the dose range of 10−6–10−1 C mm−2. The surface analysis results are correlated with electron dose dependent secondary electron yield (SEY) and electron stimulated desorption (ESD) yield measurements. Electron induced surface modifications are caused by a surface cleaning through ESD and a simultaneous accumulation of a carbonaceous contamination layer. The changes in the elemental surface composition are determined by the different kinetics of both processes. ESD yields decrease drastically with electron dose while carbon is accumulated on the surface with a constant rate. Initially a surface cleaning through ESD, in particular of hydrogen, is the dominant process. This surface cleaning causes a strong reduction of the SEY and of ESD yields. When the electron dose exceeds 10−4 C mm−2 the electron beam induced carbon layer growth becomes the dominant process and the SEY is further reduced to values which are below those of an atomically clean metal surface.