Traps deep hole trap

The difference in stabilities of cation radicals located on G, GG, and GGG sequences was initially investigated by Sugiyama and Saito [14], who employed ab initio methods to calculate the gas phase ionization potentials of nucleobases stacked in B-DNA geometries. Their results indicated large differences in potential for holes on G vs GG (0.47 eV) and GGG (0.68 eV) sequences. A similar G vs GG difference was calculated by Prat et al. [62]. These values suggest that GG and GGG are, in fact, deep hole traps and they have been widely cited as evidence to that effect [54, 63]. 

The main elements of the energy landscape for positive charge transfer mentioned above are shown in Figure IB, using the fragment of the DNA duplex schematically depicted in Figure 1A as an illustration. In this particular case, the doublet G Gg is an example ofthe deep hole trap, sites G., and G exemplify intermediate states, while sites Tj, T, T, and Tg correspond to "bridging"states. 

The electron transfer reaction 5.12 takes place between the SCN ion and the OH radical when both are adsorbed at the surface of the same Ti02 particle. Consideration of the yield of the radical dimer in reaction 5.13 permitted an estimate of the redox potential of the surface-bound OH radical, Ti02- 0H, of about h-1.5 V vi. SHE. It is therefore a strongly oxidising species, yet a rather deep hole trap, lying -1.3 eV above the valence band of Ti02. The pA a of Ti02- 0H, as defined by reaction 5.14, was estimated to be 2.S-2.9. 

Sevilla et al. have shown that HO is not detected in relatively dry DNA (F < 8), but is detected in the F > 8 waters per nucleotide, suggesting that all holes do not transfer to DNA in the regime (8 > F > 22). The sites where these holes are initially produced are not particularly good hole traps. The holes move about until they encounter deep traps such as guanine. 

One can assume that the saturated residual potential, at the end of a large number of cycles, decays. As thermal release proceeds, holes are emitted and swept out from the specimen, resulting in a decrease in the measured surface potential. The decay rate of the saturated potential is strongly temperature dependent due to thermal release from deep mobility gap centers, located approximately 0.9 eV above for holes. The discharge of the saturated potential due to electron trapping occurs much more slowly. The reason is that the energy depth of electron traps from is about 1.2 eV, which is greater than that of hole traps from E. ... 

Fig. 3. Schematic energy level diagram of a p+-n junction showing the edges of the space-charge region, x = 0 to x, and x = x2 to W, within which a deep trap does not trap and emit carriers. EFp and EF are the quasi-Fermi levels for holes and electrons.

Rhodium, incorporated in the silver halide grains, decreases sensitivity and increases contrast. This action has been attributed to depression of latent image formation because of deep electron trapping by the trivalent rhodium ion (183-185). Eachus and Graves (184) showed that rhodium, probably as a complex, acts as a deep trap for electrons at room temperature. Weiss and associates (186) concluded that the rhodium salts introduce deep traps for both electrons and holes. Monte Carlo simulation showed that the photographic properties could be accounted for in this way over a wide range of exposure times. 

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