A hybrid model for coating and charging of submicron particles submerged in a CH4-H2 plasma

摘要

Summary form only given. In the framework of material processing, plasma chemical vapor deposition represents an attracting route for surface modification of submicron particles. However, a great deal of effort has yet to be invested to render such processes efficient. An important step is clearly defined by pursuing a better understanding of the physics occurring in proximity of such particles. This can be offered by predicting the complete details of the plasma behavior by use of numerical simulations. In the present work, we consider a submicron particle submerged in a reactive and dense CH₄/H₂ plasma, for which the characteristic length scales, (i.e., the mean free path of species (lambda_mfp) and the Debye length (Lambda _De)), are of the same order of magnitude (lambda_mfp ~ Lambda_De). Therefore, at a distance far from the particle, the continuum model can be implemented, whereas in vicinity of the particle we will make use of particle-in-cell (PIC) method along with Monte Carlo collision (MCC) simulation approach. In particular, we will adopt the MC null collision method to account for collisions of electrons and ions with neutral species, whereas we will model the screen-Coulomb interactions via the time-implicit MCC algorithm proposed by Cranfill et al. In the former, the probability of collision is obtained upon calculation of collision frequencies from information regarding local neutral gas properties (e.g., T and P), cross sections for the electrons/ions-neutral collisions as a function of energy, and the charged species velocities. In the latter, the collisional scattering is modeled as a statistical rotation of the momentum vector, where the relative rotational angle represents the accumulation of many small random deflections. Such rotation needs to satisfy the generalized Ohm's law on the average. Finally, a matching condition will be formulated to provide continuity between the two re-gions