Low pressure arcing on graphite: evidence of a columnar growth within the cathode spot

Abstract

Summary form only given, as follows. Graphite cathode sources are used in arc ion plating devices for diamond-like film synthesis. A series of experimental studies and recent modeling results have been published on the problem of the detrimental co-emission of macro-particles from these sources. These suggested the emitted spherical carbon particles were a result of the local plasma conditions above the surface leading to the high pressure and temperature requirements for liquid droplet ejection, followed by a process similar to metallic electrodes. Contrary to this mechanism, this paper first presents SEM and Raman spectroscopy observations of carbon columnar growth layers formed on the cathode spot surface during the residence time of the carbon arc plasma. The emitted particles seem to originate from the cauliflower structure observed on the top layer of this growth. Cross sections of the cathode spot craters and film will be shown, with structure evolution passing from amorphous carbon at the base of the columnar structure to a dominating Raman peak of diamond at the top surface. Characteristics of the growth with varying source material morphology, their macro-particle emission behavior and arc mobility will be given together with modeling results of the plasma properties above the surface. Graphite materials showing important macro-particle emission show good correlation with decreasing spot mobility, increasing spot crater diameter and increasing growth layers. A self-sustained cathode spot model is used to evaluate the operating conditions at the plasma-surface interface.