Resonant Raman scattering of amorphous carbon and polycrystalline diamond films

Resonant Raman scattering has been used to study amorphous carbon and polycrystalline diamond films. The incident photon energies were varied over the range 2.2--4.8 eV. In hydrogenated amorphous carbon films containing both sp³- and sp²-bonded carbon, a high-frequency shift is observed for the main Raman peak with increasing photon energies up to 3.5 eV. This shift is interpreted in terms of scattering from {π}-bonded carbon clusters which is resonantly enhanced for photon energies approaching the {π}-π* resonance of sp²-bonded carbon. In polycrystalline diamond films excitation with photon energies {≥}3.0 eV enhances the Raman signal from the sp³-bonded diamond phase relative to the scattering by sp²-bonded carbon and with respect to the underlying broadband luminescence. The Raman band arising from scattering by sp²-bonded carbon shows a high-frequency shift with increasing photon energy for energies {≥}3.0 eV. Possible models for the structure of this sp²-bonded carbon phase are discussed on the basis of the present Raman data.