STRUCTURE AND DYNAMICS OF THE CU(001) SURFACE INVESTIGATED BY MEDIUM-ENERGY ION-SCATTERING

The structural and vibrational properties of the Cu(001) surface at te mperatures between 107 and 685 K have been determined by medium-energy ion scattering (MEIS). At less than or equal to 305 K, a top-layer co ntraction (Delta d(12)) of -2.0% is found. Above 520 K the contraction may be slightly larger at -2.3%. Small second-layer expansions (simil ar or equal to +1%) exist. Monte Carlo modeling of the data shows that the vibrations of the Cu(001) surface atoms are strongly enhanced ove r those of the bulk, with ratios of surface to bulk vibrational amplit udes increasing from similar to 1.6 at 107 K to more than 2.0 at 685 K . Analysis of multiple-scattering geometries which preferentially prob e either the in-plane or the near-perpendicular vibrational amplitudes shows anisotropic surface vibrations at all temperatures examined. La ttice vibration correlation effects have been included in the analysis . The in-plane vibrational amplitude changes from 11% to 37% larger th an the perpendicular vibrational amplitude over the temperature range studied. The effect on the results of isolated, diffusing Cu adatoms o n the surface at high temperature is considered. Due to the influence of the methods of data reduction upon the results, an analysis of the ion energy loss in the high-resolution MEIS energy spectra is presente d.