Abstract:

Based on thermodynamical and kinetic theories, the mechanism of synthesizing ultra-fine diamond in graphite suspension by ms-pulsed laser irradiation was analyzed. Diamonds were nucleated by condensation in the carbon vapor plume formed when ms-pulsed laser irradiated on the graphite particles. Compared to ns-pulsed laser, ms-pulsed laser with a lower laser energy density and a longer pulse width provided a smaller degree of supercooling for the growth of diamond nucleus, allowed rather low growth velocity for diamond nucleus. On the other hand, sp2 hybridization on diamond surface could reduce the surface energy of diamond nucleus and make them more stable. However, the formation of sp2 hybridized structure retarded the epitaxy growth of the nanodiamonds, thus preventing the formation of large grains. Above two factors could determine the formation of ultra-fine nanodiamonds during the synthesis process by the irradiation of ms-pulsed laser. Our results suggested that the growth of nanodiamonds follows Wilson-Frenkel law, and ms-pulsed laser with lower energy density was propitious for producing fine nanodiamonds.

Key words: Nanodiamond, Pulsed laser, Thermodynamics, Kinetics