TABLE 2.

The classification of plasma sources.

CP	Generating mechanism and characteristics	References
Dielectric barrier discharges (DBD)	Plasma occurs between two electrodes, and then, an AC high voltage is applied on the electrodes. It is an excellent CP source with 1–10 eV and high density.	(32)
Gliding arc discharge	Two (or more) metallic electrodes connected to an AC or DC high-voltage transformer. A plasma plume is generated when the high voltage is applied. This arc is then pushed away by a gas flow and glides along the electrodes until it collapses.	(33)
Plasma jet	Two coaxial electrodes, between which gas flows at high rates. The free electrons are accelerated by the RF field and collide with molecules of background gas. These inelastic collisions can produce various reactive species (excited atoms and molecules, free radicals) that exit the nozzle at high velocity.	(25, 34)
Corona discharge plasma jet	Containing substantial electric field for expediting the ionization energy of arbitrarily produced electrons to that of milieu gas atoms or molecules.	(29)
Microwave (MW)/radio frequency (RF) plasma	RF plasma is usually achieved when a gas is placed within an oscillating electromagnetic field, produced by an induction coil or distinct electrodes kept outside the reactor. MW/RF CP is usually generated under reduced pressure.	(35, 36)