Semiconductor counters

Cadmium fluoride has similar uses to the zinc halide. Cadmium oxide is used in ceramic glazes the sulfate, as a source of other cadmium compounds and in the radio valve industry the sulfide is important as a yellow pigment for artists, and is used in the paint, soap, glass, textile, paper, rubber and pyrotechnics industries. Cadmium sulfide in admixture with other compounds such as the selenide gives rise to other pigments of value. It is also used in phosphors and fluorescent screens and in scintillation counters. Semiconductors such as CdS... 

Anthracene and phenanthrene are stereoisomers that are crystals in pure form. Anthracene is a pale yellow crystal, while phenanthrene exhibits a yellow to brown hue. Besides its common name, anthracene is referred to as anthracin, green oil, or paranaphthalene. The compound is commercially produced by recovery from the coal tar distillation fraction known as anthracene oil or green oil. Anthracene is the key ingredient in the production of anthraquinone. However, it and phenanthrene are also used for the manufacture of dyes, fibers, plastics, and wood preservatives. ° Phenanthrene, also known as phenanthrin, can be produced by high-temperature fractional distillation of coal tar oil. It is additionally used for the oxidation of diphenic acid for use in polymers, as well as the production of chemical softeners, explosives, and some pharma-ceuticals. Recent research has extended the application of both isomers to scintillation counters, semiconductors, and photoconductors. ... 

In the past, specifications for metal ion content and particles have been arbitrarily reduced for each new generation (smaller geometry) of devices. Recently, research has been conducted on the correlation of device performance with various impurities. While impurity specifications will continually drop, only troublesome impurities will be reduced. This change in strategy of purity management will reduce the burden on chemical suppliers, especially as specifications move toward 1 part per trillion (ppt) for metals and to the theoretical limits of particle size detection of optical counters. Semiconductor Equipment and Materials International (SEMI) has recently initiated an effort to reduce the number of specified metals down to 17 (Table 15.4) from over 30. 

The X-ray fluorescence spectrum is then registered on a photographic film or by Geiger, proportional or scintillation counters, semiconductor detectors, etc. 

Figure 8.28 shows how the X-rays fall on the solid or liquid sample which then emits X-ray fluorescence in the region 0.2-20 A. The fluorescence is dispersed by a flat crystal, often of lithium fluoride, which acts as a diffraction grating (rather like the quartz crystal in the X-ray monochromator in Figure 8.3). The fluorescence may be detected by a scintillation counter, a semiconductor detector or a gas flow proportional detector in which the X-rays ionize a gas such as argon and the resulting ions are counted.

The cadmium chalcogenide semiconductors (qv) have found numerous appHcations ranging from rectifiers to photoconductive detectors in smoke alarms. Many Cd compounds, eg, sulfide, tungstate, selenide, teUuride, and oxide, are used as phosphors in luminescent screens and scintiUation counters. Glass colored with cadmium sulfoselenides is used as a color filter in spectroscopy and has recently attracted attention as a third-order, nonlinear optical switching material (see Nonlinear optical materials). DiaLkylcadmium compounds are polymerization catalysts for production of poly(vinyl chloride) (PVC), poly(vinyl acetate) (PVA), and poly(methyl methacrylate) (PMMA). Mixed with TiCl, they catalyze the polymerization of ethylene and propylene. 

Benchtop X-ray energy dispersive analyzer BRA-17-02 based on a gas-filled electroluminescent detector with an x-ray tube excitation and range of the elements to be determined from K (Z=19) to U (Z=92) an electroluminescent detector ensures two times better resolution compared with traditional proportional counters and possesses 20 times greater x-ray efficiency compared with semiconductor detectors. The device is used usually for grits concentration determination when analysing of aviation oils (certified analysis procedures are available) and in mining industry. 

The photoelectrolysis of H2O can be performed in cells being very similar to those applied for the production of electricity. They differ only insofar as no additional redox couple is used in a photoelectrolysis cell. The energy scheme of corresponding systems, semiconductor/liquid/Pt, is illustrated in Fig. 9, the upper scheme for an n-type, the lower for a p-type electrode. In the case of an n-type electrode the hole created by light excitation must react with H2O resulting in 02-formation whereas at the counter electrode H2 is produced. The electrolyte can be described by two redox potentials, E°(H20/H2) and E (H20/02) which differ by 1.23 eV. At equilibrium (left side of Fig. 9) the electrochemical potential (Fermi level) is constant in the whole system and it occurs in the electrolyte somewhere between the two standard energies E°(H20/H2) and E°(H20/02). The exact position depends on the relative concentrations of H2 and O2. Illuminating the n-type electrode the electrons are driven toward the bulk of the semiconductor and reach the counter electrode via the external circuit at which they are consumed for Hj-evolution whereas the holes are dir tly... 

Detector Type U, Th, Pa, Ra Semiconductor Single ion counter Multiple-Faraday + single or multiple-ion counters Single ion counter Multiple-Faraday + single or multiple-ion counters Single ion counter Multiple-Faraday + single or multiple-ion counters Multiple-Faraday + single ion counter... 

The sensitizers display a crucial role in harvesting of sunlight. To trap solar radiation efficiently in the visible and the near IR region of the solar spectrum requires engineering of sensitizers at a molecular level (see Section 9.16.3).26 The electrochemical and photophysical properties of the ground and the excited states of the sensitizer have a significant influence on the charge transfer (CT) dynamics at the semiconductor interface (see Section 9.16.4). The open-circuit potential of the cell depends on the redox couple, which shuttles between the sensitizer and the counter electrode (for details see Section 9.16.5). 

Domestic consumption of selenium in 1981 exceeded 453,000 kg. About 50% was used in electronic and copier components, 22% in glass manufacturing, 20% in chemicals and pigments, and 8% miscellaneous (Cleveland et al. 1993). In 1987, world production of selenium was about 1.4 million kg (USPHS 1996). In 1986, 46% of the global selenium produced was used in the semiconductor and photoelectric industries 27% in the glass industry to counter coloration impurities from iron 14% in pigments and 13% in medicine, in antidandruff shampoos, as catalysts in... 

Excitation of sample by bombardment with electrons, radioactive particles or white X-rays. Dispersive crystal analysers dispersing radiation at angles dependent upon energy (wavelength), detection of radiation with gas ionization or scintillation counters. Non-dispersive semiconductor detectors used in conjunction with multichannel pulse height analysers. Electron beam excitation together with scanning electron microscopes. 

As discussed above, the measurement of characteristic y rays is very similar to the methods used in EDXRF. Early studies used a scintillation counter, typically a crystal of sodium iodide containing a small amount of thallium (Tite 1972). y ray absorption by these counters produces visible light, which is converted into an electrical pulse using a photosensitive detector. More recently semiconductor detectors have been used, either a lithium drifted germanium crystal, or, more typically, a pure ( intrinsic )... 

One of SACHEM s products is tetramethylammonium hydroxide (TMAH), which is sold to semiconductor industries. Suspended particles in TMAH solutions could cause severe mechanical damage to the electronic devices manufactured by their customers. The determination of the particle content in such solutions is therefore critical. It is performed with a laser-equipped particle counter, which provides 70% detection efficiency. The counting must take place in a clean room because tiny airborne particles can land in the solutions and give them a false high reading. A class 1000 environment is required in this case, which means that the count of particles in the air that are greater than or equal to 0.5 jrm in diameter must be less than 1000 per cubic foot. Typically, a customer s specification for TMAH solutions is less than 100 particles per milliliter for particles greater than or equal to 0.5 fim in diameter. 

Upon absorption of light an electron from the HOMO of the adsorbed dye, D, is raised to the LUMO from where it is injected into the conduction band of the n-type semiconductor and transferred to a counter electrode where an oxidant, O, is reduced. From the reduced species, R, the electron is transferred to the HOMO of the adsorbed dye to fill the electron vacancy, so that after the overall photoelectro-chemical process the dye is in its original oxidation state. Vlachopoulos et al. (1987) have reported on Ti02 photoelectrodes that were sensitized to visible light with various dyes and that showed high quantum yields of interfacial electron transfer under visible irradiation. 

Fujishima and Honda reported the splitting of water by the use of a semiconductor electrode of titanium dioxide (rutile) connected through an electrical load to a platinum black counter-electrode. Irradiation of the Ti02 electrode with near-UV light caused electrons to flow from it to the platinum counter-electrode via the external circuit. 

Figure 11.8 Schematic diagrams of the Fujishima-Honda cell using an illuminated Ti02 (rutile) semiconductor electrode and a platinum counter-electrode...

In this type of DSSCs, once the dye is photoexcited, charge separation drives electrons from the valence band (vb) of the semiconductor to the photoexcited dye. Common to both types of DSSCs is the regeneration of the oxidized or reduced dye by a redox mediating electrolyte. The latter is mainly in the form of a liquid and/or a solid. Platinum films deposited onto ITO or FTO are the most utilized counter-electrodes and are required to close the electronic circuit. 

Uses Dyes starting material for the preparation of alizarin, phenanthrene, carbazole, 9,10-anthraquinone, 9,10-dihydroanthracene, and insecticides in calico printing as component of smoke screens scintillation counter crystals organic semiconductor research wood preservative. 

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