Raman spectroscopy of ion irradiated diamond

Ion irradiation experiments of diamond samples at room temperature have been performed by using in situ Raman spectroscopy as diagnostic technique. Different ions are used with energies of 200 or 400 keV. The area of virgin diamond Raman band (at 1332 cm-1) decreases exponentially as the ion fluence increases. This is due to changes in the optical properties of the damaged samples in the visible spectral range. Results from different ions demonstrate that this effect is correlated with the number of displacements/cm2, i.e., with the energy lost by ions through elastic collisions with target nuclei. Amorphous carbon (sp2) is formed after a threshold of about 2x1022 vacancies/cm3, or about 16 eV/C-atom deposited by elastic collisions. The peak position and full width at half maximum of the D line and G line of the synthesized amorphous carbon are studied. In particular, the G-line peak position shifts from the initial 1545 cm-1 to about 1515 cm-1 at the higher doses. The results are also discussed in view of their relevance in astrophysical environments