Orientation dependence of core edges from anisotropic materials determined by inelastic scattering of fast electrons

Abstract

Electron-energy-loss spectra have been measured in the region of the $K$ edges in graphite and hexagonal boron nitride. The fine structure is found to be strongly dependent on the crystal orientation and momentum transfer. Angular distributions of peaks in the spectrum have been recorded from crystals with the $c$ axis parallel and at 45° to the beam direction. These agree well with the theoretical distributions for transitions to ${\pi }^{*}$ and ${\sigma }^{*}$ final states in a hybridized atomic-orbital model. Peaks in the energy-loss spectrum are compared with band calculations of the ground-state density of states. Some correspondence is found between these but there is also evidence of core excitons.