A leed crystallographic analysis for the Cu(100)-(2 × 2)-S surface structure

An intensity analysis with low-energy electron diffraction is reported for the (2 × 2) surface structure obtained by the adsorption and presumed dissociation of H 2S on the (100) surface of copper. Intensity-versus-energy curves were measured with a video LEED analyser for five diffracted beams at normal incidence and for eleven beams at an off-normal direction with a polar angle of incidence equal to 14°. Comparisons were made with intensity curves calculated with the renormalised forward scattering method for three types of structural models in which the metal atoms remain in their regular bulk positions. The best correspondence between experimental and calculated intensities occurs with sulphur atoms adsorbed in the “expected” 4-coordinate adsorption sites. The reliability index proposed by Pendry is minimised with S atoms 1.32 Å above the topmost metal layer; this corresponds to nearest-neighbour S-Cu bond distances equal to 2.24 Å. This value appears broadly consistent with a measurement by photoelectron diffraction, as well as from model predictions.