Capacitively coupled discharge works similarly to DC glow discharge. They both rely on the electric field created by the voltage applied on the electrodes to accelerate free-moving electrons to knock out bonded electrons in neutrals. Thus, they are categorized as “E-discharge” in comparison with “H-discharge” (inductively coupled discharge). Unlike DC discharge, there is no fixed cathode or anode in capacitive discharge. An alternating high voltage is applied on both electrodes. The majority of the free-moving electrons will be oscillating back and forth. Compared with DC discharge, they will have less chance of absorption by electrodes and a higher chance of ionizing neutral particles. Thus, capacitive discharge offers higher ionization efficiency than DC discharge.