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)×${10}^{16}$ ions/${\mathrm{cm}}^2$. With increasing implantation damage, the triply degenerate one-phonon Raman mode at 1332 ${\mathrm{cm}}^{\mathrm{-}1}$ broadens and shifts down to around 1300 ${\mathrm{cm}}^{\mathrm{-}1}$. This corresponds to a broad peak in the one-phonon density of states predicted for Raman scattering from an amorphous ${\mathit{sp}}^3$ carbon network. Additional Raman peaks appear at 1451, 1498, and 1634 ${\mathrm{cm}}^{\mathrm{-}1}$. 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 ${\mathrm{cm}}^{\mathrm{-}1}$, correspond well with the density of states of an amorphous carbon network of mostly fourfold bonded carbon with some localized threefold bonding.