A helium diffraction study of the structure of the Ni(115) surface

Abstract

Hard wall and soft wall potentials have been used to analyze helium diffraction data from Ni(115). From this analysis, we have determined the equipotential surface which is simply related to the electron charge distribution at the surface. Corrugation functions for the hard wall as well as the repulsive and classical turning point corrugation functions for a corrugated Morse potential have been compared with electron density contours calculated from atomic superposition. The corrugation functions determined from soft and hard wall potentials have the same shape and differ only slightly in their maximum amplitudes. This shows that the hard wall model is suitable for structural studies even on strongly corrugated surfaces. The shape of the surface corrugation is not in agreement with electron density contours calculated for bulk termination. Large surface relaxations can bring the shapes of the corrugation function and the electron density contour into good agreement. However, we conclude that these relaxations are physically unreasonable and that electron delocalization rather than shifts in atom position primarily determine the shape of the electron density contour at the surface.