毫秒脉冲激光合成超细纳米金刚石

通过热力学和动力学的基本理论, 分析了毫秒脉冲激光照射石墨悬浮液合成超细纳米金刚石的机理. 在毫秒脉冲激光与石墨颗粒相互作用形成的碳蒸气羽中, 通过碳蒸气凝聚形成了金刚石核. 与纳秒脉冲激光相比, 毫秒脉冲激光具有较低的功率密度和较长的脉宽, 为金刚石核的生长提供了较小的过冷度, 使得金刚石核的生长速率减小; 而较小的生长速率也为金刚石表面形成sp2杂化结构提供了机会, 它可以有效降低金刚石核的表面能, 促使金刚石核稳定, 但表面的sp2杂化也阻止了金刚石核的外延. 以上两个原因决定了毫秒激光辐照石墨颗粒过程中只能获得超细的纳米金刚石.

Ultra-fine Nanodiamonds Synthesized Using Millisecond-pulsed Laser

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.