Single-reflection layer-scattering theory of low energy electron diffraction spectra

Abstract

A simple general method for computing medium and low energy electron diffraction (LEED) spectra of layered materials has been developed for application to transition metal dichalcogenides. Electron transmission and reflection coefficients for each individual sheet of atoms are computed; the separate sheets are grouped into sandwiches which are stacked upon one another to form the crystal; the intersheet scattering is treated with the single-reflection approximation. For an unrelaxed lattice whose sandwiches are separated by the distance b and whose intrasandwich layers are separated by a, the scattered electron intensity is ‖ f (a) ‖ 2 S (b), where f (a) is the single-sandwich form factor for the outermost sandwich. Lattice relaxation of the surface sandwich slightly modifies this result. The static structure factor S (b), which is a spiked function of energy and contains mainly bulk structural information, produces the principal peaks in the intensity versus energy spectrum, but the surface sandwich reflectivity ‖ f (a) ‖ 2 smoothly modulates the peak intensities and contains most of the surface structure information. This method of fitting ‖ f (a) ‖ 2 should be contrasted with most LEED analyses that concentrate on fitting peaks [which are related to S (b) and actually contain little surface structure information]. This simple single-reflection analysis of the surface structure is confirmed by a complete multiple scattering calculation.