Surface parameters of clean nickel (001) determined by LEED averaging

Abstract

The low-energy electron diffraction from clean Ni(001) has been studied in detail over a large range of temperature and diffraction geometries with particular emphasis on the reproducibility of the data and internal consistency of the analysis. Averaging the data at constant momentum transfer extracts the kinematic intensity for both the specular and non-specular beam. The results are analyzed to obtain both structural and electron diffraction parameters. The electron total attenuation coefficient and its energy dependence are determined from both the widths of peaks in the averaged data and from the integrated elastic intensity and are consistent with one another and with previous determinations for Ni(111) and Ni(001). While both the inner potential and the relaxation of the interplanar spacing cause shifts in peak positions, their effects can be separated in the analysis because the latter also causes changes in the relative peak intensities and in the peak shapes. The resulting inner potential, as well as its energy dependence, agree with earlier determinations for Ni(111) and with theoretical calculations to within an uncertainty of about 2 V. From analysis of peak shapes in the averaged data, it is concluded that the surface interplanar spacing is within ±4% of the bulk interplanar spacing at 380 K. This result agrees with estimates obtained from dynamical theories. It is shown that the excess atomic thermal vibrations near the surface, and not experimental uncertainties, limit the accuracy to which this spacing can be determined.