Sheath characteristics in plasma carrying finite mass negative ions and ionization at low frequency

The sheath characteristics are investigated in a collisional environment by considering three electronegative plasmas, namely CF₄, Oxygen, and C₆₀ plasmas. Specifically, positive ion velocity, electrostatic potential, charged species densities and net space charged density are examined inside the sheath region with the variation of collisional parameter, mass ratio of negative to positive ions, temperature ratios of electrons to positive ions and electrons to negative ions, non-neutrality parameter and negative ion density. Collisional cross-section is assumed to have a power-law dependence, and both the cases of constant mobility and constant collisional cross-section are discussed and compared. In order to introduce the concept of finite mass of negative ions, both kinds of ions are considered to be governed by their fluid equations, where contribution of ionization, attachment, and detachment is also taken through the continuity equations.