Energy loss of fast protons specularly reflected from metal surfaces

We have calculated the mean energy lost by protons of 120 keV that are specularly reflected at an aluminum (1 1 1) surface. For this impact energy, the main contribution to the energy loss is due to the excitation of conduction band electrons. The response of these electrons to the proton electric field can be accurately treated within linear response theory. Therefore, we have studied the importance of improving the model for the response function of conduction band electrons by using two different models. One of the models considered here is semiclassical whereas the other is fully quantum mechanical. The results obtained with both models have been compared with each other and recent experimental data. For this particular impact energy, the more realistic quantum mechanical model provides better agreement with experiment at the higher incidence angles, where the calculated ion trajectories are more reliable