Oscillating behavior of proton scattering amplitude on an electron-stimulated-desorbed surface of KBr by keV electrons

Abstract

Specular yields of 15 keV protons scattered from a KBr(001) electron-stimulated desorbed surface for 1.5–5 keV electron irradiation have been measured, whose periodic oscillations are resulting from the layer-by-layer removal by surface erosion. In each oscillation, the first half-period is found to elongate compared with subsequent half-periods. This elongation indicates that extra electron fluence is needed for the initiation of the surface erosion. The elongation depends on the irradiation electron energy and decreases with the elevating temperature of the sample. From the extra electron fluence irradiated during the elongation, the amount of F centers accumulated in the thin surface layers rise to 30% of the number of alkalis on the topmost layer. This high number of F centers indicates that, before the initiation, the growth of aggregated F centers takes place in numerous heaped F centers under the flat surface, as though the X centers are sinks of F center-diffusion.