Particle coating low-pressure Ch/sub 4/H/sub 2/ plasma: The effect of particle size

Summary form only given. In recent years, material processing technologies have been remarkably improved by the ever-growing research interest and efforts in nano-science along with plasma processing techniques. In particular, low-pressure plasma has been widely employed in the coating industry due to its capability of efficiently generating active species, responsible for layer deposition, in a low temperature environment (300 K to 600 K). These physical conditions are particularly suitable for surface modification of micron/sub-micron size particles, which are the important constituents of different classes of materials. The possibility of many combinations of particle and coating materials, and range of operating conditions, make the physico-chemical phenomena of coating complex. Consequently, a great deal of efforts has to be invested in developing predictive models capable of defining the optimum conditions for coating of such particles. In the present work, a hybrid model of kinetic theory and continuum theory for predicting coating of particles by plasma enhanced chemical vapor deposition in low-pressure conditions is used to study the effect of particle size on the physical processes occurring during deposition (i.e. particle charging, distribution of species in the particle surrounding, and layer deposition). In particular, we focus our interest on large particles. The chemical reaction model considers a CH₄/H₂ plasma consisting of 31 reactions that accounts for ionization and dissociation reactions, namely electron-neutral, ion-neutral, and neutral-neutral reactions. Ions and electrons are responsible for particle charging and for generation of self-bias electric field, whereas radicals account for particle layer growth. In a spherical symmetric geometry, up to a distance longer than one mean free path from the surface of the particle, reactive-diffusive phenomena occur and continuum theory is implemented to solve for species transpo- t. Whereas, inside the so-called vacuum sphere around the particle no collisions occur and kinetic theory is applied