The inelastic scattering of He and Ne from a (001) surface of sodium fluoride

Abstract

The inelastic scattering of He and Ne atoms from a cleaved (001) surface of NaF has been studied at different surface temperatures. The study was similar to that for the He–LiF system, in that the intensity of the inelastic streaks in the vicinity of diffraction peaks was explored as a function of detector location and crystal rotation. For diffraction peaks not too close to the normal the phonon emission and absorption effects separated into regions on either side of the elastic peak, the latter events being on the side closest to the normal. At 140°K the phonon absorption events were less probable than phonon emission events, i.e., atoms tended to lose energy while at higher surface temperature the probability of energy gain increased. The positions of the streaks moved predictably in space by varying the incident momentum of the beam, a parameter which also influenced the intensity of the streaks. Comparisons have been made to the He–LiF system using the elastic constants of the two materials.