Paper is often used in the course of criminal activities, including kidnapping, bombings, forgery, conspiracy, threatening letters, and gambling. Thus the examination of paper is a common task for the document examiner [1].
Photoelectromagnetic and photoconductive lifetimes have been measured from 77° to 300°K in monocrystalline ^-type indium antimonide of net acceptor concentration ranging from less than 10 16 cm -3 to 10 18 cm -3 . It is concluded that at the lower temperatures, excess electrons are trapped in immobile states in the forbidden band and that the trap concentration is the same in all samples, regardless of net acceptor concentration. At intermediate temperatures, trapping becomes negligible but recombination continues to take place through states in the forbidden gap; there is some reason to believe that in this temperature region lifetimes are determined by more than one level of forbidden-band states. At still higher temperatures, where the samples are intrinsic, the lifetime data are consistent with the hypothesis of a direct interband Auger recombination process.
We have observed modulation of the dark current in Bii2Si02c (BSO) as a function of prior irradiation, and a time-varying absorption of radiation that is dependent upon prior irradiation. As a result of these observations and the previously reported observations of photoconductivity, photorefractivity, photosensitivity, and mobility modulation, a model theory of transport has been developed that requires multiple sources of defect/impurity energy levels. A hopping band exists in the forbidden energy gap where these levels coincide. Transport via exchange of charge is possible here, analogous to conduction via hopping in the presence of impurity bands or dense concentrations of defects. Traps capable of containing immobile charge carriers occur where these various levels do not coincide. Large mobility variations can occur as a result of photon-induced modulation of the Fermi level. Much of the phenomena observed in BSO can be explained through interaction between the multiple defect/impurity energy levels.
The electron density of a pure InSb crystal has been synthesized using very accurate x-ray diffraction intensities. After subtracting the electron density of the palladium core from both kinds of atoms, the distribution of the valence electrons was determined. By this means it was established that, on the average, 0.45±0.05 electrons are transferred from the Sb atoms to In atoms, as compared to a transfer of 0.34 or 0.42 electrons deduced from infrared absorption measurements. The effective ionic charge to be used in polar-scattering calculations for InSb was calculated to be 0.17±0.02 e based on the electron density, as compared to 0.18 e or 0.16 e determined from electron mobility measurements.
A two-dimensional light modulator has been developed based on the principle of photon controlled electroplating of metal onto a photoconducting semiconductor. It may be used in transmission or reflection, and forms positive or negative images. Some observed characteristics of the modulator are: 18-line pairs/mm resolution, reusability to the extent of about ten cycles, and image formation time of 0.5-5 sec. Other experimental observations are described, and device performance is analyzed in terms of semiconductor parameters.
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