TABLE OF CONTENTS Amorphous materials can best be defined as materials in which the three dimensional periodicity is absent. The atomic arrangement is not entirely random as in gases and there is a short range order of a few ngstr m units. As with crystalline solids, amorphous materials can be insulators, semiconductors or metals, and in some cases at very low temperatures they can even be superconductors [1, 2].
One of the outstanding optical applications of amorphous semiconductors is in electrophotography, commonly known as xerography [3 5]. The photosensitive insulating device employed in xerography is known as a photoreceptor. As schematically illustrated in Figure 4.1, there are five major steps involved in the xerography process: (a) sensitisation of the photoreceptor by a corona discharge; (b) image-wise exposure of the photoreceptor to produce a latent electrostatic image; (c) development of the latent image by fine toner particles; (d) transfer of the developed image to plain paper; and (e) fixation of the transferred image by fusing [6].
Improved methods of transferring print to paper have been established for applications such as word processing, electronic mail and high quality facsimile. Laser printers satisfy the desirable characteristics of high speed, graphic flexibility and high print quality because of the electronic controls and laser optics involved. He-Ne lasers together with external acousto-optic modulators may be used to modulate the light beam with the information to be printed.
The exposure unit for laser printers is more sophisticated than that of...
