MeV-ion axial surface-channeling from an electron irradiated KCl(0 0 1) surface

Surface-channeling of protons incident with 5 mrad on an electron-irradiated surface is investigated using a 0.55 MeV beam of protons. The target surface is KCl(0 0 1), which is damaged by electron-stimulated desorption with 5 keV electron irradiation. The direction of the incident beam is adjusted along the <1 0 0> and <1 1 0> channeling conditions and the channeling-dips of the scattering yields are observed. The irradiation dose-dependence of the minimum yields and widths of the dips is measured. Two dips are compared, i.e., for the <1 0 0> and <1 1 0> channelings. By increasing the irradiation dose up to 2 x 1016 cm-2, the dip around the <1 0 0> axis becomes opened, but that of the <1 1 0> axis becomes shallow. The irradiated surfaces are observed to have many overlapped terraces of sub-micron with monolayer steps. The surface morphology deformed by the irradiation effects to truncate trajectories of the <1 0 0> channeling protons. This roughness of the surface is more effective for the trajectories of the <1 1 0> channeling protons. The protons incident on the rough surface along the <1 1 0> axis are not reflected from the atomic row but reflected by a potential of the surface with steps. Results by a simple computer simulation of the trajectories of protons at stepped surfaces also indicate the scattering processes.