Raman scattering from MeV-ion implanted diamond

Single-crystal diamond has been irradiated with 4-MeV carbon ions to doses in the range (0.5--130)×{}10¹⁶ ions/cm². With increasing implantation damage, the triply degenerate one-phonon Raman mode at 1332 cm^-1 broadens and shifts down to around 1300 cm^-1. This corresponds to a broad peak in the one-phonon density of states predicted for Raman scattering from an amorphous sp³ carbon network. Additional Raman peaks appear at 1451, 1498, and 1634 cm^-1. These do not correspond to any previously observed peaks in carbon materials and may be unique to implantation above 1 MeV. These three peaks, together with the Raman scattering below 1300 cm^-1, correspond well with the density of states of an amorphous carbon network of mostly fourfold bonded carbon with some localized threefold bonding.