Determination of the structure of adsorbed monolayers by the energy-averaging method: Al(100)

Abstract

The energy-averaging technique proposed by Tucker and Duke for the determination of the unit-cell geometry of adsorbed monolayers is verified for a model of strong scatterers on a substrate described by the lattice parameters and muffin-tin lattice potential characteristic of Al(100). The analysis is based on the inelastic-collision model in which three phase shifts (associated with s, p, and d-waves) are used to describe elastic electron interactions with the atomic scatterers, and an inelastic collision penetration depth, λ ee, determines the consequences on the elastic scattering of inelastic collisions of the incident electron. The technique is tested by comparing certain averages of scattered intensities calculated using the complete (dynamical) model with the predictions of a kinematical calculation based on the same model electron-solid interaction. Within this framework, for λ ee ⩽ 4 Å, the energy-averaging technique provides an adequate determination of the monolayer unitcell geometry to within an accuracy of ± 0.10 Å independent of the values of other parameters in the model electron-solid force law. The technique remains qualitatively valid but yields geometrical parameters with reduced accuracy for values of λ ee up to about 8–10 Å. To within this accuracy, it also may be applied to determine either the geometry of the upper layer of a clean surface for given atomic scattering factors or the atomic scattering factors themselves if the surface layer geometry is known a priori (as in the case of monatomic metals).