Spatial evolution of EEPFs in a millimetre scale radio frequency argon plume

Abstract

The characteristics of a plume expanding from a 13.56 MHz rf hollow cathode discharge in argon were investigated using a compensated Langmuir probe and an emissive probe. Particular attention was paid to the spatial evolution of the electron energy probability function (EEPF) and its relationship to the local plasma potential. It was found that the plasma emerges from the source with a Maxwellian distribution before becoming bi-Maxwellian further downstream. Eventually, the EEPF returns to a single temperature when the low energy electrons have diffused to the point where they are not present in sufficient quantity to be measured. By creating a zero-dimensional iterative model to study the EEPF, it was determined that contrary to expectations, inelastic collisions in the diffusion chamber are unlikely to be responsible for the modification of the EEPF.