Low-Energy-Electron-Diffraction Intensity Profiles and Electronic Energy Bands for Lithium Fluoride

Abstract

Model calculations of the low-energy-electron-diffraction (LEED) intensity profiles for LiF (100) and of the bulk electronic energy bands for LiF are performed using model potentials with quite different degrees of ionicity. One potential is constructed using ${\mathrm{Li}}^0$ and ${\mathrm{F}}^0$ free-atom charge densities and the other is constructed using ${\mathrm{Li}}^{+}$ and ${\mathrm{F}}^{-}$ free-ion charge densities. Although both model potentials yield rather similar band gaps, the photoemission threshold and LEED measurements clearly favor the ${\mathrm{Li}}^{+}$ ${\mathrm{F}}^{-}$ form of the potential. Experimental LEED intensity profiles for LiF (100) at $T=573\mathrm{}$ °K are analyzed, and certain features strongly suggest that the top lithium and fluorine sublayers do not lie in the same plane but are separated by about 0.25 Å in a direction normal to the surface. In order to motivate further experimental work, additional intensity profiles are calculated for both the perfect surface model and the reconstructed surface model.