Impact-parameter dependence of energy loss for 625-keV H+ ions in Si single crystals.

Abstract

The energy distributions for 625-keV ${\mathrm{H}}^{+}$ ions transmitted through thin Si single crystals are studied for detailed angular scans through the 〈110〉 and 〈100〉 axial as well as the {111} and {110} planar channels. Well-resolved structures in the distributions taken near the 〈110〉 axial direction are observed. The experimental energy-loss distributions are very well reproduced by a Monte Carlo simulation using the semiclassical approximation model for core electrons and the two-component free-electron-gas model for valence electrons. The best fit to the data is obtained if the model energy losses are scaled up for core electrons and down for valence electrons by several percent. The experimental distributions can also be reproduced by assuming the mean excitation energy for distant collisions of the ion with core electrons equal to 1.4 times the binding energy for a given shell. No significant differences between the distributions obtained using the solid-state and free-atom valence electron densities have been found. The evolution of the distributions for the 〈110〉 axial scan is discussed in terms of ion trajectories and the flux distribution. Also, the azimuthally averaged mean energy loss is studied as a function of tilt angle with respect to the 〈110〉 axis.