Energy and momentum transfer of He atoms scattered from a lithium fluoride crystal surface

Abstract

Both the energy transfer and the normal and tangential force coefficients for scattering of a nearly monoenergetic beam of He atoms (incident energy Ei=63 meV) from a clean single crystal LiF(001) surface have been measured under wind tunnel conditions in the range of surface temperatures from 300 to 720 K. Expressions are derived for the differential reflection coefficient for a realistic He-LiF(001) potential with the inclusion of multiphonon processes, and these expressions are used to calculate the average energy and momentum transfers as well as their higher moments. The comparisons between theory and experiment indicate the presence of a moderate degree of surface roughness. The measured recovery temperature depends on incident beam angle and is significantly larger than expected for complete or partial accommodation, in good agreement with the theoretical calculations.