Correlation of electron self-energy with geometric structure in low-energy electron diffraction

Abstract

In low-energy electron diffraction (LEED) studies of surface geometries where the energy dependence of the intensities is analyzed, the in-plane lattice parameter of the surface is usually set to a value determined by x-ray diffraction for the bulk crystal. In cases where it is not known, for instance in films that are incommensurate with the substrate, it is desirable to fit the in-plane lattice parameters in the same analysis as the perpendicular interlayer spacings. We show that this is not possible in a conventional LEED I(E) analysis because the inner potential, which is typically treated as an adjustable parameter, is correlated with the geometrical structure. Therefore, without having prior knowledge of the inner potential, it is not possible to determine the complete surface structure simply from LEED I(E) spectra, and the in-plane lattice parameter must be determined independently before the I(E) analysis is performed. This can be accomplished by establishing a more precise experimental geometry. Further, it is shown that the convention of omitting the energy dependency of the real part of the inner potential means geometrical LEED results cannot be trusted beyond a precision of approximately 0.01 Å.

Low-Energy Electron Diffraction With Energy Invariant Carrier Wave Wavenumber Modulated by Exchange-Correlation Interaction

“…LEED experience shows that the precision is limited by the elastic electron-atom scattering (EEAS) phase shifts injected as input to the diffraction codes. [1][2][3] In a new study of EEAS we set up a KKR (Korringa-Kohn-Rostoker) muffin-tin (MT) potential with overlapping MT spheres corresponding to N ieq symmetrically inequivalent atoms in the surface structure. It is clear that N ieq radial overlaps give rise to 2N ieq degrees of freedom due to overlapping MT sphere radii and possible energy shifts of atomic potentials.…”