Charging of Insulator Surfaces by Ionization and Transport in Gases

Insulator surfaces in gases collect charge when the rate of charge arrival exceeds the rate of conduction by the insulator from the surface region. The source of the collected charge may be in close proximity to, and hence greatly influenced by, the surface. Alternately, the source may be remote so that it releases charge independent of the surface accumulation. For the latter arrangement, charge transport through the gas greatly influences where it is collected. Surface charging is desired in some situations, such as for producing images or for processing. Charging is undesirable and hazardous in other situations; for example, where electrical failure may be triggered. A third possibility makes use of surface charge collection as a diagnostic procedure for materials and transport studies. This paper is concerned with the basic production and accumulation of surface charges from the adjacent gas and presents results on the processes involved. Transport parameters of drift, diffusion, and spacecharge effects are considered. Examples of charging and measured distribution under different conditions, including saturation effects, are analyzed.