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 sp high 3 and sp high 2 bonded carbon, a high-frequency shift is interpreted in terms of scattering from pi-bonded carbon clusters which is resonantly enhanced for photon energies approaching the pi-pi resonance of sp high 2 bonded carbon. In polycrystalline diamond films excitation with photon energies equal or bigger than 3.0 eV enhances the Raman signal from sp high 3 bonded diamond phase relative to the scattering by sp high 2 bonded carbon and with respect to the underlying broadband luminescence. The Raman band arising from scattering by sp high 2 bonded carbon shows a high-frequency shift with increasing photon energy for energies equal or bigger than 3.0 eV. Possible models for the structure of this sp high 2 bonded carbon phase are discussed on the basis of the present Raman data.