Raman microspectroscopy of diamond crystals and thin films prepared by hot-filament-assisted chemical vapor deposition

Abstract

Diamond crystals and thin films were prepared by thermal decomposition of methane and hydrogen, in the presence of a hot tungsten filament. Raman microspectroscopy investigations were carried out and correlated to scanning-electron-microscopy observations of the crystallization. It is shown that the diamond Raman signal of individual cubo-octahedric crystals depends on their orientation with respect to the substrate and on disorder upon growth. The influence of growth processes on the diamond Raman signal is considered and, in particular, contamination effects by hydrogen and tungsten impurities are emphasized. As the film crystallization deteriorates from an assembly of faceted crystals to that of blunted crystals and then to that of ball-like elements, the intensity of the diamond Raman line decreases and broad bands appear. The appearance of these broad bands is attributed to the presence of an amorphous carbon phase with atoms hybridizing with ${\mathit{sp}}^{2}$ and ${\mathit{sp}}^{3}$ bonds.