Energy loss-of fast protons specularly reflected from metal surfaces

We have calculated the mean energy lost by protons of 120 keV that are spec ularly reflected at an aluminum (1 1 1) surface; For this impact energy, th e main contribution to the energy loss is due to the excitation of conducti on band electrons. The response of these electrons to the proton electric h eld can be accurately treated within linear response theory. Therefore, we have studied the importance of improving the model for the response functio n of conduction band electrons by using two different models. One of the mo dels considered here is semiclassical whereas the other is fully quantum me chanical. The results obtained with both models have been compared with eac h other and recent experimental data. For this particular impact energy, th e more realistic quantum mechanical model provides better agreement with ex periment at the higher incidence angles, where the calculated ion trajector ies are more reliable. (C) 1999 Elsevier Science B.V. All rights reserved.