Nano size effects in the high resolution electron energy loss spectra and excitation function of hydrogenated diamond films

The present work studies the high resolution electron energy loss spectra (HR-EELS) and excitation function of hydrogenated diamond films composed of diamond grains of varying size of ∼ 300, ∼ 20 nm and ∼ 5 nm. It is reported that HR-EELS modes associated with C-C lattice phonons are comparably more intense than modes associated with the C-H surface vibrational modes in the case of nano-crystalline compared to micro-crystalline diamond films. Excitation function measurements of the different modes show a pronounced maximum at ∼ 8 eV for the nano-diamond films, whereas for micro-crystalline films similar modes showed maximum intensities at 13 eV with a smaller contribution at 8 eV. It is reported that the elastic electron reflectivity is substantially larger for the nano-diamond films, showing broad maxima at ∼ 8 and ∼ 13 eV in both cases. It is suggested that these effects are associated with the larger probability for inelastic scattering of electrons by lattice phonons mediated by scattering with internal grain boundaries and defects in the case of nano-crystalline diamond films.