Correlations between energy flux and thin film modifications in an atmospheric pressure direct current microplasma

Abstract

A custom-built atmospheric pressure direct current microplasma discharge was designed utilizing Au coated Si3N4 transmission electron microscopy (TEM) grids as electrodes to enable a direct imaging of the plasma treated anode and cathode surfaces. Significant differences between the anode and the cathode, as well as between Ar or He operation of the microplasma, respectively, were observed already by examination of the electrode surfaces by light microscopy. Scanning electron microscopy as well as TEM imaging revealed details such as grain growth and changes in surface morphology. The energy fluxes from plasma towards the anode and cathode were determined and correlated with the surface modifications. As expected from structure zone diagrams higher energy fluxes result in higher degree of crystallinity even at atmospheric pressure. Furthermore, ions and their respective energy contributions were identified to play a major role for the surface modification, despite their low kinetic energy due to the large number of collisions. Depending on the working gas, Ar or He, the identified energetic contributions of the total ion energy flux change and, subsequently, result in visible differences in the plasma treated Au films.