Charge generator

As in most electrophilic reactions, the abiUty to stabilize the positive charge generated by the initial addition strongly affects the relative rates. MX reacts faster than OX and PX because both methyl groups work in conjunction to stabilize the charge on the next-but-one carbon. Sulfonation was, at one time, used to separate MX from the other Cg aromatic isomers. MX reacts most rapidly to form the sulfonic acid which remains in the aqueous phase. The sulfonation reaction is reversible, and MX can be regenerated. 

Fig. 7. The field-dependence of the charge-generation efficiency of a 2.0- lm thick (0) a l.l-).tm thick ( ), and 1.8-).tm thick (A) fuUerene/PMPS film obtained with positive charging and 340-nm irradiation (A). The soHd lines are calculated from the Onsager model. The best-fit curve is obtained with Tq = 2.7 nm and = 0.85. Also plotted is the charge-generation efficiency of a fuUerene/PVK film (+) obtained with positive charging and 340-nm irradiation (B). The soHd lines are calculated from the Onsager model. The best-fit curve is obtained with = 1.9 nm and = 0.9 (13).

Table 3. Charge-Generation Efficiency of Selected Polymeric Photoconductors ...

Experimental Values of Charge-Generation Efficiencies. In this section the charge-generation efficiencies of many polymeric photoconductors are compared (Table 3). When the experimental data has been fitted to the Onsager model, the initial electron—hole separation distance,... 

The intrinsic charge-generation efficiency of polymers is often low and needs to be enhanced by the addition of sensitizers. The sensitizer can be dissolved in the polymer to enhance the bulk charge-generation efficiency of the polymer. Effective sensitizers include 2,4,7-trinitro-9- uorenone [129-79-3] (TNF), hiUerene, thiapyryhum dye, CdS nanoclusters, etc (Table 3). Molecular stmctures of selected sensitizers are shown in Figure 8. 

Recently photorefractivity in photoconductive polymers has been demonstrated (92—94). The second-order nonlinearity is obtained by poling the polymer doped with a nonlinear chromophore. Such a polymer may or may not be a good photoconductor. Usually sensitizers have to be added to enhance the charge-generation efficiency. The sensitizer function of fuUerene in a photorefractive polymer has been demonstrated (93). 

Since surfactant-type antistats function by attracting atmospheric moisture to the plastic, the relative humidity (rh) has a significant effect on antistat performance (Fig. 6). Relative humidity also has an effect on charge generation (Table 7). 

Table 7. Effect of Relative Humidity on Charge Generation...

The performance characteristics of ceramic sensors are defined by one or more of the foUowing material properties bulk, grain boundary, interface, or surface. Sensor response arises from the nonelectrical input because the environmental variable effects charge generation and transport in the sensor material. 

Some of these devices have a respectable quantum efficiency of charge generation and collection, approaching 0.4 (20). The nature of the polymeric binder has a large effect on the device performance (21), and so does the quaUty and source of the dye (22). Sensitivity to the environment and fabrication methods results in some irreproducibiUties and batch-to-batch variances. However, the main advantage of the ZnO-based photoreceptor paper is its very low cost. 

Fig. 6. Classes of charge-generating dyes and pigments (a) perylenes, (b) thiapyrylium, (c) phthalocyanines, (d) squaiaines, and (e) a2o. R and Z are organic...

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