Scattering of Helium Atoms by Phonons in the (001) Surface of LiF at 150°K

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Abstract
Results are presented for the scattering of a beam of helium atoms (obtained from a nozzle source) from a cleaved lithium fluoride surface maintained at 150°K. The scattering patterns reveal two types of scattering events: (1) coherent scattering, showing a large number of diffraction peaks not reported to date, and (2) inelastic scattering resulting from the vibrations of surface atoms. This component of scattering is observed in the neighborhood of the elastic peaks, in the form of streaks, extending in particular directions outward from the Bragg angle. The shapes of the scattering patterns obtained follow the general predictions made for bounds imposed on the scattering surface by the incident velocity of the helium atom.