ELECTROPHOTOGRAPHIC PROCESSES IN ZNO LAYERS

The principles and applications of electrophotography have been described in several monographs(1-3) as well as in numerous journal articles.(4,5) It is not the intention here to compete with these publications, or to provide an overview of the main electrophotographic processes known today, but rather to try to work out the materials related aspects of the electrophotographic process of Electrofax layers. Since Electrofax layers are composed of fine ZnO particles, which are coated and held together by an organic binder material, the study of their electrical and photoelectrical properties is extremely complicated and has not been explored in complete detail. Therefore, certain questions will remain unanswered and, hopefully, will induce further work in this field. After a general introduction into the electrophotographic process, we shall seek to facilitate the understanding of them, and separate the various physical processes, by discussing the discharge of photoreceptors and some models and approximations to the physical situation relevant to Electrofax layers. A review is then given of the pertinent electrical properties and defects of the bulk of ZnO and of the surface properties, including dye sensitization. The following section is devoted to the properties of polycrystalline ZnO layers. In a final section, the electrophotographic processes are discussed, such as charging, dark and light induced decay of the surface voltage and some photographic properties. © 1979.