| Popis: |
Over the past few decades the interest in quasi two dimensional Van der Waals materials such as highly oriented pyrolytic graphite (HOPG) increased significantly, especially the electronic structure is of great interest for many applications. This work aims to investigate the unoccupied band structure above the vacuum level of HOPG by means of double differential inelastic very low energy electron diffraction (IVLEED) measurements in the energy range of 0 to 200eV primary energy in 30° and 60° specular reflection geometry. This allows to study the band structure with elastically and inelastically back scattered primary electrons as well as measuring the secondary electron emission. Using the matching formalism, a correlation between the elastic peak intensities and the band structure was established. The link with inelastic intensities provides a qualitative description of the penetration depth of the primary electrons in the crystal. The acquired IVLEED data revealed the existence of a novel and atypical feature, in which primary electrons occupy a preferred final state, resulting in the emission of electrons with fixed energy. Two kinetic models for inelastic diffraction of electrons on crystals have been implemented, in which the sequence of inelastic and elastic diffraction lead to Bragg peaks at different energies. The results are in good agreement with quantum field theory models and experimental data for high energies [1–5]. |
