Electron energy-loss spectral analysis of diamond and diamond-like carbon films

The characteristic electron energy-loss features of hydrogenated diamond-like carbon materials (a-C:H) and crystalline diamond films have been studied. The a-C:H films were grown by radio-frequency self-bias plasma-enhanced chemical vapor deposition from methane. The a-C:H films had hydrogen concentrations from 28 to 44 at. % and mass densities from 1.45 to 1.68 g/cm3. We find that in the a-C:H samples, increasing hydrogen content increases the fraction of carbon sp3 sites. The crystalline diamond films were grown by hot-filament-assisted chemical vapor deposition and the hydrogen concentration in these samples is less than 1 at. %. The electron energy-loss spectra showed the diamond films were a mixed phase material containing both a diamond-like phase and crystalline diamond. The main energy-loss peaks for the diamond-like component are caused by π and (π+σ) electron plasma resonances in the ranges from 3.3 to 4.4 eV and from 21.1 to 23.2 eV, respectively. The mass density of the diamond-like component in the crystalline diamond films as determined from the energy of the (π+σ)- plasmon is approximately 1.9 g/cm3. The characteristic energy loss features of crystalline diamond are the band-gap transition of about 5 eV and the surface and bulk plasmon energy losses at 23 and 34 eV, respectively. A σ-electron interband transition peak from the valence band to the conduction band in the energy range from 14–17 eV has been observed from both diamond-like and crystalline diamond films.