Chapter 4 - Cold Plasma Discharges

Abstract

This chapter presents various features that are associated with realistic plasma that one can obtain in practice. The cold plasmas are usually created and maintained by direct current (DC), radio frequency (RF), or microwave power applied to a gas at low pressures. The treatment of a real plasma discharge in a reactor is not easily amenable to analytical or even numerical approaches, because of the variety of complex interactive phenomena. This chapter aims to obtain approximate behavior of the real plasma by simple physical reasoning. The most important feature in a cold plasma discharge is the appearance of a plasma sheath adjacent to the substrate or the wall. The plasma sheath is a region consisting of predominantly cations and owes its appearance to the difference in mass between the cation and the electron. The potential is virtually constant in the plasma except at the plasma sheath where it acquires a negative potential with respect to the plasma. A pre-sheath within which the cations acquire enough kinetic energy to move towards the cathode connects the plasma sheath and the plasma region in the discharge to one another. The physical and chemical nature of the plasma, which is affected by the different mechanisms available for the generation of electrons in the discharge, are discussed in the chapter.