Random and channeling stopping powers of He and Li ions in Si

In this work we have measured the electronic stopping powers of He-4 and Li-7 ions for channeling and random directions in Si as a function of the incident ion energy. The channeling ([100] for Li, [110] and [111] for Li and He) and the random (Li only) measurements cover a wide energy range between 200 keV and 9 MeV. The Rutherford backscattering technique together with different multilayer targets has been employed in the present experiments. The results are compared to calculations carried out in the framework of the unitary convolution approximation, which takes into account the impact-parameter-dependent energy loss for each projectile charge state, with further refinements including screening effects in close collisions between the electrons of the target and the screened projectile.