Surface exciton population in proton impact with LiF(100)

We have recently shown that the large energy loss experienced by slow proto ns interacting with a LiF surface is primarily caused by the population of surface excitons [11]. These states are most probably populated by electron transfer from H- ions formed at halogen sites, whereas secondary electron emission results from direct detachment of the negative ions in collisions with halogen sites. We report here on the impact energy dependence of the c harge-state of the scattered projectile, its energy loss and the associated electron yield. From these complete measurements, the transfer probability to the surface excitons and its dependence upon impact energy is derived i n the range 0.6-10 keV. (C) 2000 Elsevier Science B.V. All rights reserved.