Modeling of particle generation in laser ablation plasma

In this study, we used the general dynamic equation (GDE) for aerosols, combined with particle charging by positive ions and electrons, to simulate particle generation in laser ablation plasmas. The population balance equations based on Brownian coagulation and diffusion charging theory were represented by using a discrete-sectional model. The temporal evolution of the particle size distribution was simulated at three different initial number concentrations of neutral monomers, positive ions and electrons, as well as at two different gas pressures.The simulated average particle size increased with time and with increasing initial concentration of neutral monomer and gas pressure. The particle growth was affected by the particle charging when both number ratios of positive ion to neutral monomer and of electron to neutral monomer are higher than 0.1. Simulated particle size distributions were compared with SEM images of particles collected at different sampling points and gas pressures in actual plasmas operating at conditions similar to those simulated. Changes of particle size with increasing distance between the target and the sampling point and with increasing the pressure were well reproduced by simulations. However, particle diameters calculated were much smaller than SEM images because physical values, such as, initial concentrations of monomer, positive ions and electrons and the recombination probability of electron and positive ions, used in calculations were invalid.

► Simulation of particle generation in laser ablation plasmas by the general dynamic equation. ► The population balance equations based on Brownian coagulation and diffusion charging theory. ► The particle size increased with time, initial concentration of monomer and gas pressure. ► The particle growth was affected by the particle charging under some conditions.