Detection System for KeV Proton Beam Scattered from an ESD-surface with Monolayer Pits of Alkali Halide Crystal

To observe specular oscillations in ion-surface scattering originating from layer-by-layer desorption of an electron stimulated desorbed (ESD) surface, a 15 keV proton beam was impinged on the surface with an angle of incidence less than 1°. We prepared an experimental system to examine the scattering yields of reflecting protons by conveniently employing a fluorescent screen to view scattering yields (scattering patterns) and a commercial digital camera for yield measurements. Because the present energy of the proton beam was too low to illuminate the screen, a micro-channel plate was inserted in front of the screen. Measurements with electron irradiation show obvious damping specular oscillations; the widths of angular distributions of scattered protons simultaneously oscillated with increasing electron fluence. From the measured periods of the oscillations, the ESD rates of thermal desorption from KBr(001) at 1.5 keV electrons irradiation were obtained for sample temperatures.