Analysis of the composite structures in diamond thin films by Raman spectroscopy

Diamond and diamondlike thin films produced by various chemical-vapor-deposition processes have been examined using Raman spectroscopy. These films exhibit features in the Raman spectra, suggesting that they are composites of crystalline and amorphous diamond and graphitic structures. The components of this composite structure that contribute to the Raman scattering are discussed in terms of ${\mathrm{sp}}^2$- and ${\mathrm{sp}}^3$-bonded structures. The use of Raman spectroscopy as a technique for estimating the ${\mathrm{sp}}^2$-to-${\mathrm{sp}}^3$ bonding ratio is considered. Powder composites of BN-diamond and graphite-diamond have been studied as a means of modeling the films, and a simple theoretical model of the Raman scattering from these samples is proposed. From these results it is shown that it is necessary to make assumptions about the domain size of the graphitic ${\mathrm{sp}}^2$ regions. It is found that the Raman scattering associated with ${\mathrm{sp}}^2$ bonding in the films is much stronger than that from single-crystalline or microcrystalline graphite structures. Shifts of the vibrational modes are also observed. The optical and vibrational properties of the ${\mathrm{sp}}^2$ component in the films implies a different atomic microstructure. A model of the ${\mathrm{sp}}^2$-bonding configurations in the films is proposed which may account for the observed features in the Raman spectra.