Amorphous structure compared with crystalline one is in lack of the longrange orderness but still has the short-range orderness. This leads to the concept of “ bandtails ” in the energy gap state (developed by Mott) — the most relevant characteristics in the amorphous semiconductors.
Mechanisms of electrical conductivity, processes of high field conduction and of switching, optical absorption, photoconductive properties, photostructural change and photo-doping process in amorphous semiconductors are reviewed from the viewpoint of electronic band scheme. Applications of amorphous semiconductors to electronic devices, e.g., switching devices and memory cores, and to xerographic techniques are also reviewed.

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Six polypyrimidines were prepared from p-Xylylpyrimidine(l) with p-phenylenediamine (P1, PDA), benzdinene (P2, BD), diaminodiphenylether (P3, DPE), diaminodiphenylmethane (P4, DPM), diaminodiphenylsulfone (P5, DPS) and hexamethylenediamine (P6, HDA). These polymers prepared by polycondensation of carbonyl group and amino group have pyrimidine rings and azomethine in the main chain.
The relationship between chemical structure of polypyrimidines and dark- and light-decay characteristics of surface charge was discussed.
The dark- and light-decay of the surface charge by the negative corona discharge for polypyrimidines were observed. The decaying rates of the sureface potential were found to be in the following order; DPM > PDA > HDA > BD > DPE > DPS for dark decay, DPS > DPE > BD for light decay. The ratio of light decaying constant was found to be greater in the following order; DPS > DPE > BD.

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SUMMARY
In electrophotography, corona charges on photoconductive layers are preferable to show slow decay in the dark and quick decay by the exposure of image light. It is important, therefore, to clarify the theory and mechanism of dark and light decay for the improvement, of electrophotographic paper and equipment.
In this paper, some theoretical analyses and experimental verifications are given on the mechanism of dark decay of corona charges on ZnO-resin type photoconductive layers. The surface charged ZnO-resin layer is composed of electrode capacitance charge Qe and bulk capacitance Charge Qb. The dark decay curve is consisted of three ranges; avalanche-, electrode capacitance- and space charge capacitance-discharging ranges.
At the beginning of dark decay, the surface charge Qe is discharged by the leakage of avalance current. A linear relation between 1/(V-V_n) and decay time t is expected theoretically in this range, where V_n is the avalanche breakdown potential of the layer. After the avalanche range, the surface charge Qe is discharged by the ohmic leakage current. A linear relation between log(V-V_m)and decay time t is expected in this range, where V_m is the value of surface potential at the end of this range. In the final range, the sureface charge Qb is discharged also by the ohmic leakage current. A linear relation between logV and decay time t is expected in this range. The above three relations between V and t were proved to hold in experimental results.

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Isotherms of adsorption by zinc oxide of Rose Bengal dye from different solvents such as water, ethnol and water-ethanol mixtures were measured. The different amounts adsorbed at saturation were obtained from these isotherms, and the minimum adsorption value was obtained at about 70 vol.% of ethanol, which gives the minimum enthalpy of the mixed solvents. The maximum amount of dye adsorbed was obtained in the case of the pure water solvent, and the maximum coverage θ_BET(max) was about 0.5.
The dependence of the surface potential and the photovoltage of the dyed zinc oxide powder layers prepared by vaporization of solvents on the amounts of dye adsorbed was measured in air. The plots of the surface potential vs. the amount adsorbed showed M-shaped curves, and the plots of the photovoltage vs. the amount adsorbed showed N-sharped curves. Form these results, it was proposed that two types of adsorption sites for the sensitizing dye may exist on the zinc oxide sureface. The adsorption states of the dye molecules on the surface and the mechanisms responsible for the dye-sensitized photovoltages were dicussed.

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