MICROCRYSTALLINE DIAMOND PHASE BY LASER-ABLATION OF GRAPHITE

We report the first evidence for the production of crystalline phases of diamond using laser ablation of graphite, extending an earlier report in which amorphous carbon or hydrogenated amorphous carbon films were produced using pulsed excimer radiation and hydrogen at a pressure of up to 100 Torr. Here, the ablating laser radiation was 308 nm, 40 mJ pulse-1, 10 pulses s-1 in hydrogen at 10 Torr and was simultaneously used to process heteroepitaxial film growth on silica optically. On the basis of transmission electron diffraction, it is proposed that nucleation occurs via the formation of SiC at the interface, analogous to results on silica using chemical vapour deposition. The morphology, revealed by scanning electron microscopy, shows micron-sized crystals of predominantly cubic orientation, with octahedral components. Raman spectroscopy shows a little graphitic character, but lacks the characteristic 1332 cm-1 line; the absence of this feature is assigned to the reduction in symmetry of the microcrystalline morphology, because of either structural or chemical effects.