IMPACT PARAMETER DEPENDENCE OF THE ELECTRONIC STOPPING POWER FOR CHANNELED IONS

In order to examine the dependence of the electronic stopping power (dE/dx) on the impact parameter p, the energy dissipation of axially channeled ions with curved trajectories is studied theoretically by means of a cluster model. dE/dx is accounted in the framework of nonlinear molecular dynamics (MD) coupled with the local density approach (LDA) based on the Lindhard-Winther (LW) theory. A correction factor of 2 is introduced to compensate the lower dE/dx, especially for low-energy ions. B ions are implanted into Si [100] and [110] at incident energy in the region 10 keV less-than-or-equal-to E0 less-than-or-equal-to 10 MeV. Results are the following. Firstly two kinds of solid-state effects on the p-dependence of dE/dx are found at high and low E0, respectively. At high E0 (> 100 keV) the core electrons reveal quite different profiles of dE/dx versus p than valence ones, and at low E0 (< 100 keV) the topological difference in the electron distribution among axial channels appears in those profiles, which cannot be explained by means of collisions with single atom. Secondly, the p-dependence of dE/dx is intended to adapt the simple form dE(p)/dx = A exp (-sp/a). The factor s due to core electrons increases distinctly with E0, while that due to valence electrons is almost invariant, smaller than 0.3.