Sheath formation criterion in collisional electronegative warm plasma

Abstract

In this paper, the sheath formation criterion for three different electronegative plasmas, namely CF4, O2 and C60 plasmas, has been numerically investigated under the collisional atmosphere for the planer probe geometry. Here, the behaviour of both the ions: positive and negative, are described with the fluid approach. The dependency of momentum transfer collisional cross section on the ions' velocity is governed by the power law. The impact of ions' temperature, negative ions' concentration and the mass ratio of negative to positive ions on the electric potential profile, ions' velocity profile and sheath thickness is analysed for distinctive cases of the power factor. It is found that the sheath thickness is reduced significantly with increasing collisional parameter and mass ratio of negative to positive ions. A significant reduction in the sheath thickness is observed with an increment in negative ions' temperature and concentration, however, this is enhanced with the increasing positive ions’ temperature. The density profile of charged species in the sheath regime is evaluated. The impact of power factor is found to be significant for the higher magnitude of the collisional parameter. Additionally, the comparison between the results for behaviour of negative ions with their Boltzmann distribution and fluid approach has been attempted herewith and a noteworthy difference is realized. The comparative studies for the cases of different and same cross-sections of both the ions and their different collisional frequencies are also conducted.