The force acting on a spherical particle moving towards aplanar wall in the near-wall region of a low-pressure plasmaprocessor

Abstract

Analytical results are presented concerning the force acting ona spherical particle which is moving towards the wall of a planar plate inthe near-wall region. The problem is assumed to be within thefree-molecule regime, and a combined specular and diffuse reflection atthe plate and/or particle surface is included in the analysis. It has beenshown that the action force on the near-wall particle contains two terms.The first term depends on the gas pressure and the plate-wall/gastemperature ratio, but is independent of the speed ratio or themacroscopic relative velocity between the particle and bulk gas. Only thesecond term is directly proportional to the speed ratio or the relativevelocity. Consequently, the action force on the near-wall particle movingtowards the planar plate may be negative or positive, i.e. the particlemay be decelerated or accelerated, depending on the case conditions. Aslong as the gas temperature is different from the plate-wall temperature,the near-wall particle will always experience a force even for the casewithout relative motion between the particle and bulk gas.