Photoreceptors surface layers

Fig. 4. Photoinduced-discharge (PID) curves of a-Si H photoreceptor (multiple-layer type), (a) Surface voltage plotted as a function of exposure tim e for the following light intensities at 600 nm (1) 1.6 fiW cm-2, (2) 0.32, (3) 0.16, and (4) 0 08. (b) The photocurrent (estimated from the time derivative of the PID curves) versus surface voltages for a-Si H photoreceptor (a-Si B, 10 ppm, 10 /an thick exposure 600 nm, 2.0 X 1012 photons cm-2 sec-1). [From Oda eta/. (1981b).]...

Fig. 10.26. Typical structure of a xerographic photoreceptor showing the blocking layer at the substrate, the surface layer and the photoconductor (Pai 1988).

Organic photoreceptors can be prepared in either a flexible web or drum format. Webs are usually prepared on polymer substrates, polyethylene tere-phthalate being the most common. The substrates are between 100 to 200 pm in thickness and coated with a conducting surface layer. The substrates often contain layers on the reverse side for reduced curl, static discharge prevention, and control of frictional characteristics. The web configuration is also widely used for laboratory studies. For drums, the substrate is a metal cylinder, usually Al. Recently, however, drums of a poly(phenylene sulfide) resin doped with conductive C black have been developed (Kawata and Hikima, 1996). Drums are widely used in low- and mid-volume applications. Drums, however, are not well suited for research purposes. Thus, the preparation and characterization of drum photoreceptors is usually related to a specific application. 

For some applications, photoreceptors are prepared with surface layers for protection from chemical, radiation, and physical damage. Most surface layers are less than 5 pm. A key electrical requirement is the conductivity. If the layer is too insulating, a residual potential will build up during cycling. Thus, this... 

Decreased charge acceptance of dual-layer photoreceptors with N,N -dipheny l-N,N -bis(3 -methylphenyl)-( 1,1 -bipheny l)-4,4 -diamine (TPD) containing transport layers after extended corona exposures has been reported by Pai and Yanus (1984). This effect was reduced by the addition of a thin polymer surface layer doped with bis-(2-methyl-4-N,N-diethylaminophenyl)phenyl-methane. Ong et al. (1989) described a similar effect with an inverse dual-layer photoreceptor. In this case, the surface layer contained an electron transport... 

Osawa and Doi (1992) described a surface layer of plasma-polymerized amorphous C over the transport layer to retard ozone interactions with the transport material along with increased transport material at the interface to compensate for any material that may be destroyed. The reasoning is that without a protective surface layer, the transport layer is destroyed by ozone but the surface is continually abraded so the cycling characteristics are relatively unaffected. However, in an overcoated photoreceptor the surface layer cannot be worn away and destruction of transport material by ozone results in a rising residual potential with cycling. This effect can be reduced by having a higher concentration of transport material at the interface. 

Overcoat layers are used to protect the photoreceptor surface from scratching and abrasion, and chemical degradation due to corona by-products [7]. Overcoats may be relatively thick polymeric layers (microns) or thin (submicron) refractory... 

Photoreceptors may be characterized by optical microscopy for layer structure and architecture. Surface defects may be characterized by atomic force microscopy. Scratch resistance can be characterized by scratching the photoreceptor surface with a stylus of known dimensions under specified loads. Brittleness measurements are... 

Another field of application for boron nitride is its use as blocking layer and/or surface layer in electrophotographic photoreceptors [69 to 96,380]. Again, these layers are produced by the CVD methods described in Section 4.1.1.10.2, p. 62. Depending on the deposition method or specific conditions, the boron nitride layers in the electrophotographic receptors may also consist of or contain p-BN [97 to 100]. 

The retina besides containing the specialized photoreceptor cell layer is a portion of CNS grey matter comprising a large surface of excitable membranes. Thus it is endowed with a high content and wide variety of polar lipids. 

The abihty to accept and hold the electrostatic charge in the darkness. The photoconductive layer should support a surface charge density of approximately 0.5-2 x 10 C/cm. The charge also has to be uniformly distributed along the surface, otherwise nonuniformities can print out as spot defects. The appHed surface potential should be retained on the photoreceptor until the time when the latent electrostatic image is developed and transferred to paper or, if needed, to an intermediate belt or dmm. In other words, the "dark decay" or conductivity in the dark must be very low. The photoconductor materials must be insulators in the dark. 

UV-irradiated cells. Using cell-free cytosolic keratinocyte extracts, Simon and colleagues26 confirmed the role of membrane oxidation in NF-kB activation. Particularly important aspects of the experimental design employed by Simon and colleagues was the use of keratinocytes versus cells derived from a cervical cancer patient, and the use of biologically relevant UVB (290 to 320 nm) radiation versus UVC (200 to 290 nm) radiation, which is filtered out by the atmospheric ozone layer and does not reach the earth s surface. Overall, these data indicate that the activation of cytokine transcription, a step essential for the induction of immune suppression, can occur independently of UV-induced DNA damage and suggest that membrane lipid oxidation can serve as a UV photoreceptor. 

JP 05197182 (Japanese) 1993 Electrophotographic Photoreceptor with Amorphous Silicon Pho-toconductive Layer Fuji Xerox Co. Ltd., Japan S Yagi et al. Copolymer useful for surface protective coating photoreceptor shows stability and gives sharp images Maleimide-terminated siloxane-imides crosslinked coatings were used to protect photoreceptors. 

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