Crystallinity effects on primary beam and Auger electron signal intensities observed for graphite

Abstract

This paper shows the experimental outcomes of a study of crystallinity dependent diffraction effects on both elastically-scattered and Auger electrons produced from highly-oriented pyrolytic graphite (HOPG) using a commercial scanning Auger electron microscope (SAM). This system is equipped with a coaxial cylindrical mirror analyser (CMA). Scanning electron images (SEM), backscattered electron images (BSE), Auger maps and the Auger spectra, using a range of relatively low incident electron energies, are obtained and analysed in detail. It is shown that the regional contrast shown in the SEM and BSE images and in the Auger maps, in the electron energy range used, is formed predominantly by forward focusing along the close-packed 〈2 1 ̄ 1 ̄ 2〉-type atomic chains of the graphite lattice. The intensity of the exiting electrons received by the CMA can be interpreted as a convolution of the diffraction of both incident and exiting electrons, e.g. that of the exiting elastically scattered electrons can vary by up to 50% on changing the incident direction of the primary beam and the orientation of the specimen. Increasing the energy of incident beam enhances forward focusing and increases the contribution from diffraction along the secondary close-packed atomic chains, e.g. the 〈3 3 04〉-type atomic chains present. The carbon (KLL) Auger electrons produced are found to behave in a way similar to the primary electrons in regard to the diffraction process but with less marked diffraction evident.