Behaviour of sheath in electronegative warm plasma

AbstractBehaviour of sheath formed on two types of probes, namely cylindrical and spherical probes, has been investigated in terms of its thickness, in front of the conducting probes immersed in an electronegative plasma for different negative to positive ion mass ratios, by considering three electronegative gases, i.e. CF4, O2 and C60. Contrary to others’ work, complete fluid equations are written for negative ions also in addition to those of positive ions considering their different masses. Increasing negative to positive ion mass ratio is found to result in an increment of the sheath thickness. The magnitude of the sheath thickness is enhanced with an increment in the positive ions’ temperature, whereas the magnitude of the sheath thickness is reduced with increased negative ions’ temperature and background density of the negative ions. The analysis of the case of a large probe radius, used in the surface-nitriding process, for both the geometries is attended. Additionally, the comparison between the results for electropositive plasma and electronegative plasma and for behaviour of negative ions with their Boltzmann distribution and fluid approach has also been attempted herewith and a noteworthy difference is realized. The case of doubly charged ions is also entertained herewith.