Paper PS1-ThM6
Plasma Induced Modification of an Organic Photoconductor in an Electrophotographic System

Thursday, November 12, 2009, 9:40 am, Room A1

The goal of this study was to elucidate structural and compositional modifications of an organic photoconductor after an extensive exposure to plasma discharge by a charging element within an electrophotographic system. An organic photoconductor, commonly found in a variety of applications ranging from simple copiers to advanced high-speed digital presses, is the key element of the modern electrophotographic printing system. It facilitates formation of the latent image resulting from the area-selective light discharge of uniformly distributed charges deposited on its surface by the plasma. Its undesirable modifications may adversely impact the print quality.

Modifications of the photoconductor's surface layer were investigated with the help of Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR) and X-ray Photoelectron Spectroscopy (XPS). The experimental set-up was designed to simulate interactions between the plasma discharge and photoconductor occurring in a typical electrophotographic printing environment. Experiments were performed over an extended period of time corresponding to printing multiple pages. UV radiation and energetic particle bombardment originating from the plasma are the two major processes responsible for the photoconductor modifications. Therefore, further elucidation of the photoconductor modification phenomenon was obtained by employing the UV-only and the particle bombardment-only experimental conditions.

A long time exposure of the photoconductor to energetic neutral and charged species, and UV photons caused massive oxidation, substantial chemical bond breakage, and reformation of bonding configuration within a thin layer below the surface. This layer can be divided into two regions corresponding to the aforementioned photoconductor modification processes. The top region, having thickness of approximately 20nm - 30 nm, is formed primarily by the particle bombardment. It is heavily oxidized and its thickness is limited by the bombardment induced sputtering. Thicker region below is relatively free of oxygen and its molecular composition is distinctly different from the original photoconductor. It is primarily formed by UV-induced cracking of the benzene rings followed by reformation of the excited radicals into new molecular species. Thickness of this region corresponds to the UV penetration depth. The possibility of preventing the formation of a parasitic surface layer will be further discussed.