Simulation of cluster formation in laser-ablated silicon plumes

Abstract

We have developed a simple model to simulate the clusters formation in laser-ablated plume in an ambient atmosphere of inert gas. The model uses the reaction-rate theory as applied to quantum oscillators in conjunction with transition state theory to synthesize and optimize the nanoparticles in the ablated plume. The evolution of cluster size is obtained by incorporating diffusion of ambient gas into an adiabatically expanding plume. Various rate constants of clustering reactions are calculated using collision rate and transition state theory. We have used the model to simulate the spatial and temporal extents of silicon nanoparticle formation in laser-ablated silicon plume generated using 248- and 532-nm irradiation in ambient atmosphere of argon. The model predicts the onset time of 3 ms with 248 nm and 1.0 Torr of argon and 2.0, 1.2, and 0.6 ms with 532-nm irradiation and argon background at 2, 5, and 10 Torr, respectively, for 1-nm clusters of silicon. The concentration of clusters decreases with an increase in distance from the target surface. The onset time dependence on ambient pressure follows a simple relation of the form {τonset∝(1∕Pambient)0.91}. The reasonable agreement of simulated results with experimental observations implies that the model is adequate to simulate Si cluster formation in the ablation plume.