Dependence of calculated low-energy-electron-diffraction intensity profiles on the depth variation of the inner potential

When an ordered overlayer is absorbed on a single-crystal substrate, model calculations indicate that the average one-electron potential within the overlayer can differ of the order of ±{}5-10 eV from that in the substrate. A simple procedure is described for estimating the effect of this phenomenon on low-energy-electron-diffraction (LEED) intensity calculations. Model calculations are presented for Ni(100)-C(2×2)-Na and Ni(100)-C(2×2)-S which illustrate the size of the effect for various incident-beam energies and angles. If the difference between the average potentials of the overlayer and the substrate is small relative to the kinetic energy of the electron associated with its motion normal to the surface, then there is little effect on the calculated intensity profiles. In particular, this means that there are appropriate ranges of beam energies and angles where one can ignore the influence of this average potential difference on determinations of overlayer geometries. This is important since presently used models for surface structural analysis do not include a consideration of this difference in potential.