Alpha-radiation damage in diamond

We studied both the extent and distrubution of structural damage in diamond crystals that was generated through either natural or artificial irradiation with alpha particles (i.e., He2+ ions with energies in the MeV range), and the related formation of colour-centres. A range of non-destructive micro-techniques was applied. The generation of damage in the (crystalline) diamond is accompanied by lattice expansion, which is detected by a down-shift of the diamond LO=TO Raman band (compare [1]). This expansion is why radiation-damaged spots at the surface of natural diamond crystals often have an up-domed shape. At high irradiation doses ≥1016 ions per cm2, diamond may be transformed locally into an amorphous state (maximum damage generated at the far ends of helium trajectories).
Visible radiation-induced green colouration of diamond (mainly caused by a broad absorption band at ∼16000 cm-1 assigned to the GR1 centre) is generated at moderate doses of 1014−1015 He ions per cm2 [2,3]. This irradiation resulted in a lowly damaged state (maximum damage ≤0.005 dpa).
[1] Nasdala et al. (1995) Eur. J. Mineral. 7, 471−478. [2] Vance et al. (1973) Miner. Mag. 39, 349−360. [3] Zaitsev, A.M. (2001) Optical porperties of diamond. Springer, 502 p.