Mass spectrometry measurements of a low pressure expanding plasma jet

The free expansion of a plasma can be used to produce a supersonic jet of neutrals and ions capable of creating thin films having specific nanostructures. The supersonic jet is generated by the pressure difference between two vacuum chambers connected through a converging nozzle. The authors acquired expansion profiles for a binary argon-oxygen mixture first starting from a neutral gas, and then from an inductively coupled plasma created inside the first chamber. The gas density was measured along the axis of the expanding supersonic jet. The gas profiles confirm the validity of an isentropic model without ending shock recompression for both the neutral gas and the plasma expansion. Ion profiles were measured for the plasma jet and show that, at the end of the supersonic jet, there is an enhancement of the local ion flux in the high energy part of their spectra.