Formation of a Double Layer in Electronegative Plasma

A double layer (DL) was observed at the boundary between the source region and expansion region of an inductively coupled, radio frequency, plasma reactor when an oxygen discharge was ignited at low pressure. A DL is a narrow localized region with relatively large potential difference and electric field, which can be formed in electropositive as well as electronegative plasmas. In an inductively coupled plasma reactor of this type, it seems to be formed at the interface between the smaller source region and the larger expansion chamber and acts as an internal boundary separating two plasma regions of significantly different compositions, density, and plasma potentials.