Simulations of electron transfer in grazing incidence ion–surface collisions

During the interaction of a low energy ion beam with a metallic surface in grazing incidence, electron transfer plays an important role in the final state of the scattered beam. In this work we compare two approaches—rate equations resolution and a Monte Carlo numerical code named ETISC1D—to describe the beam evolution and to compute the final populations of the various atomic and ionic species as well as the corresponding angular distributions. Results of both methods are compared to experimental data obtained by Hecht et al. for 2.3 keV He⁺(1s) and He*(1s2s, ³S₁) beams impinging on an Al(1 1 1) surface under 0.79° of incidence. The limitations of the rate equations method and the advantages of Monte Carlo simulations are pointed out. In particular, we show that although the rate equation approach can give a fast and rather accurate evaluation of the populations, it is unable to provide correct calculations of more sensitive quantities like angular distributions of scattered species as obtained with the ETISC1D code.