Resonant Raman scattering of amorphous carbon and polycrystalline diamond films.

Abstract

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 ${\mathrm{sp}}^{3}$- and ${\mathrm{sp}}^{2}$-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 \ensuremath{\pi}-bonded carbon clusters which is resonantly enhanced for photon energies approaching the \ensuremath{\pi}-${\ensuremath{\pi}}^{\mathrm{*}}$ resonance of ${\mathrm{sp}}^{2}$-bonded carbon. In polycrystalline diamond films excitation with photon energies \ensuremath{\ge}3.0 eV enhances the Raman signal from the ${\mathrm{sp}}^{3}$-bonded diamond phase relative to the scattering by ${\mathrm{sp}}^{2}$-bonded carbon and with respect to the underlying broadband luminescence. The Raman band arising from scattering by ${\mathrm{sp}}^{2}$-bonded carbon shows a high-frequency shift with increasing photon energy for energies \ensuremath{\ge}3.0 eV. Possible models for the structure of this ${\mathrm{sp}}^{2}$-bonded carbon phase are discussed on the basis of the present Raman data.