Stopping of low energy protons during grazing scattering from a LiF(001) surface

Protons with energies ranging from 300 eV to 25 keV are scattered under glancing angles of incidence from a flat and clean LiF(001) surface. We have recorded energy spectra for specularly reflected projectiles and analyze the data in terms of stopping cross-sections. From our analysis we deduce a threshold behaviour for electronic stopping at the low energy end. We find pronounced effects on energy loss owing to charge exchange and excitation of valence band electrons. At energies below 1 keV energy dissipation proceeds predominantly via excitation of optical phonons. (C) 2000 Elsevier Science B.V. All rights reserved.