Cathode contamination effects in a high-voltage glow discharge

Abstract

The electron emission from the cathode of a high-voltage low-pressure glow discharge, under various conditions, was studied with the aid of a simple electronemission microscope. The experiments were made in a roughing-pump atmosphere at a pressure of the order of 0.1 torr. Particular attention was paid to the influence of cathode temperature in the range 20-3OO"c. Organic contaminants appeared to spread over the cathode by an ion bombardment assisted process of surface migration at low temperatures, but decomposed to leave an immobile residue above about 1 5 0 " ~. The surface could be 'cleaned' by ion bombardment at an elevated temperature (250°c), and then appeared to remain in a relatively clean state while hot. Direct contamination from the gaseous atmosphere was not detected. This interpretation is discussed in regard to the glow-to-arc transition, to vapour-deposition processes and to vacuum breakdown.