Physics of Electrophotography

Abstract

Electrophotographic printing and copying systems are based on two wellknown but not well‐understood physical phenomena: electrostatic charging and photoconductivity. That some materials can acquire an electric charge by contact or rubbing has been known at least since the time of Thales of Miletus, around 600 B.C., and much work has been done on understanding the phenomenology of the effect, particularly in the 18th and 19th centuries; nevertheless the underlying physics of electrostatic charging of insulators remains unclear. Photoconductivity is a considerably more recent discovery, dating back only to 1873, when Willoughby Smith discovered the effect in selenium. Early work concentrated on crystalline covalent solids; only recently has the photoconductivity of highly insulating amorphous materials been studied. In fact the invention of electrophotography was a major catalyst to research in both electrostatic charging and photoconductivity.