Fundamentals and applications of ion–ion plasmas

Ion–ion plasmas can form in the late afterglow of pulsed discharges or downstream of continuous wave discharges in electronegative gases. In ion–ion plasmas, negative ions replace electrons as the negative charge carriers. In the absence of electrons, ion–ion plasmas behave quite differently compared to conventional electron–ion plasmas. Application of a radio frequency bias to a substrate immersed in an ion–ion plasma can be used to extract alternately positive and negative ions, thereby minimizing charging on device features during micro-device fabrication. Ion–ion plasmas are also important in negative ion sources, dusty plasmas, and the D-layer of the earth’s atmosphere.