激光溅射下原子团簇生长的非平衡动力学(Ⅰ)

Non-equilibrium Kinetics of Clusters Growth under Laser Ablation (Ⅰ)

以激光溅射的方式，可以产生不同尺寸与组分的原子团簇．但是对这些团簇的生长过程，却一直缺少比较深入和细致的研究．本文结合激光真空溅射石墨的实验条件，考虑了激光能量、体系膨胀、环境压力、热量辐射等诸多因素，建立了在该条件下碳原子团簇生长的物理模型，得出了相应的动力学方程的数值解．计算结果表明：每个激光脉冲溅射出约8×10－9mol（5×1015个）粒子，它们产生时的初始压力约为2×105Pa．由于扩散等因素，团簇的形成反应在785μs后已不可能进行，但是各团簇产物的产率在反应开始后0．4μs左右已达到最大值，在约1．5μs内反应即已基本完成，因为此后原子团簇的尺寸分布不再有显著的差异．

Clusters with various sizes and compositions can be produced by laser ablation in high vacuum, but the formation mechanism of the clusters under given condition still remains to be understood. In this paper, a kinetic model of clusters formed from laser ablation was suggested with considering different experimental conditions such as abating laser power, backing pressure, expansion of the laser vaporized plasma, thermal radiation and etc., and numerical solution of the relevant kinetic equation was obtained. According to the calculation, about 8 × 10-9 mole of particals can be produced from each laser pulse and their initial pressure is about 1. 9×105 Pa. Mainly due to the diffusion of the particals, formation reaction of the clusters cannot succeed at 7. 85 μs of the ablation laser pulse, but the yields of different cluster products reach their maxima at first 0. 4μs. On the whole, size distribution of the clusters is unvaried after 1. 5μs, so the formation reaction actually ends by that time.