Energy distribution of protons with primary energy of 15 keV backscattered from a Ni single crystal

Abstract

A nickel single crystal was bombarded with 15 keV protons incident in the vicinity of the and directions. The backscattered protons were energy-analysed with a spherical electrostatic analyser which could be moved around the target. The energy resolution was E/ΔE=140. The surface peak and a very low scattering intensity from the bulk was observed in a channelling experiment. The latter intensity is zero within the experimental error in double alignment. In this case it can be deduced from the width of the surface peak that less than two atomic layers contribute to it. When the angle between a close-packed direction and the incident beam is increased, at fist only the scattering intensity from the bulk increases. When a critical angle is exceeded, the surface peak increases as well. At the same time it broadens and shifts to lower energies. In addition, at energies below the surface peak new peaks in the backscattering spectra appear, Computer simulations indicate that backscattering in this energy range is governed to a great extent by multiple collisions. It is thus impossible to attribute to the observed peaks specific depths from which the backscattering occurs. The enhancement and shift of the surface peak is simulated by the calculations. They cannot, however, explain the observed structure in the spectra.