DIFFRACTION OF A BEAM OF MONOENERGETIC HELIUM-ATOMS FROM THE (001) FACE OF NICKEL-OXIDE

We detected and measured the intensities of beams of helium that were Bragg diffracted from a (001) surface of NiO kept at a temperature of 78 K. From the intensities of diffraction lines, measured up to the (2,2) order for a wide range of angles of incidence, the derivation of the gas-surface potential is attempted. For the attractive part of the potential, the position of the bound-state resonances allows the identification of three energy levels at -7.9, -4.0, and -1.6. meV, respectively. The repulsive part of the potential is approximated following a broadly accepted assumption by a rigid and hard wall. It is shown that the corrugation parameters of the wall can be systematically obtained by Fourier transforming the diffracted intensities. While the proposed analysis yields considerable qualitative information on the overall shape of the potential, with a main corrugation amplitude of about 0.14, it cannot consistently handle the full ensemble of the experimental data. The type and form of the discrepancies are pointed out in the hope that they would stimulate a more realistic solution of the optical problem, which is of increasing importance now that the molecular-beam scattering technique is becoming a universal tool to examine a large variety of surfaces. © 1979 The American Physical Society.