Impact Parameter Dependence of the Electronic Stopping Power for Channeled Ions

In order to examine the dependence of the electronic stopping power (d E /d x ) on the impact parameter p , the energy dissipation of axially channeled ions with curved trajectories is studied theoretically by means of a cluster model. d E /d x 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 d E /d x , especially for low‐energy ions. B ions are implanted into Si 〈100〉 and 〈110〉 at incident energy in the region 10 keV ≦ E 0 ≦ 10 MeV. Results are the following. Firstly two kinds of solid‐state effects on the p ‐dependence of d E /d x are found at high and low E 0 , respectively. At high E 0 (> 100 keV) the core electrons reveal quite different profiles of d E /d x versus p than valence ones, and at low E 0 (< 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 d E /d x is intended to adapt the simple form d E ( p )/d x = A exp (‐ sp / a ). The factor s due to core electrons increases distinctly with E 0 , while that due to valence electrons is almost invariant, smaller than 0.3.