DIFFRACTION OF HELIUM-ATOMS BY THE BASAL (0001) FACE OF GRAPHITE - STUDY OF BOUND-STATE RESONANCES

Elastic scattering of quasi-monochromatic He atoms from a low temperature graphite (0001) surface was observed at different incident energies. The measurements show that the periodic part of the gas-surface potential is small and well represented by the first Fourier component. This is evaluated both by the diffraction pattern and by the split specular minima associated with bound state resonances. The laterally averaged potential well contains four energy levels, corresponding to -1177, -6.13, -2.68 and -0.83 meV. For incidence along the π{variant} = 30° azimuth, shifted single minima due to the coupling of (01) and (10) resonances are observed, as predicted by Chow on the basis of symmetry arguments. Double minima appear for azimuthal angles away from the symmetry direction. Other band structure effects appearing near the resonance crossings are discussed. © 1979.