Role of electronic band structure and resonances on electron-scattering. The case of the hydrogenated polycrystalline diamond

Abstract

Elastic and inelastic scattering of low energy electrons by hydrogenated and deuterated polycrystalline diamond surfaces was studied by high resolution electron energy loss spectroscopy (HREELS). Energy loss spectra extending up to 800 meV and elastic/inelastic excitation functions, intensity variations of the elastic peak/energy-loss peaks as a function of the incident electron energy, have been measured quasi-continuously over the range 3–17 eV. Their compared behaviors are analyzed taking into account the influence of the electronic band structure of the sample. Electron elastic reflectivities are characterized by an intense broad peak at 13.5 eV incident electron energy, which results from the very high backscattering probability associated with the second absolute band gap of bulk diamond. Excitation functions of the stretching vibration mode of the hydrogen or deuterium terminations present a shoulder at about 4.5 eV and two broad peaks located around 8.0 and 12.8 eV incident electron energy. Significant resonant scattering processes contribute to the vibrational excitation at 4.5 and 8.0 eV: a strong progression of multiple excitation losses has in particular been observed in the energy loss spectrum acquired at the former energy, and a bell shape peak characteristic of a negative ion resonance has been observed at the latter energy in the stretching excitation functions. The peak at 12.8 eV is interpreted as a maximum induced by the resonant electron reflectivity enhancement, which results from the dramatic variation of the density of states corresponding to the diamond second absolute band gap.