Cadmium illuminated

The deposition takes place from HTeOs and cadmium-EDTA complex solutions at a potential whereat, whilst Te is deposited from HTeOs under a diffusion-limited condition, the Cd-EDTA complex ion is not reduced to metallic Cd. The first step is the dark deposition of one monolayer of elemental Te on the p-Si substrate (Fig. 4.11a, i). After completion of this step, as specified by measuring the charge passed, the electrode is illuminated by light with energy higher than the band gap energy of silicon for a limited time. Then conduction band electrons are... 

The metal formed is deposited on the colloidal particles and causes the absorption of the solution to increase at all wavelengtlK. The depositel cadmium is very reactive. It is reoxidized when air is admitted to the illuminated solution. Addition of methyl viologen to the illuminated solution under the exclusion of air yields the blue colour of the semi-ceduced methyl viologen, MV". As the absorption coefficient of MV" is known, the concentration of reduced cadmium can be readily calculated. reoxidises cadmium atoms ... 

Fig. 12. The hydrogen and cadmium metal concentration at various times of illumination of CdS in a 1 M sulfite solution...

Since the photophoretic force depends on the electromagnetic absorption efficiency Q y , which is sensitive to wavelength, photophoretic force measurements can be used as a tool to study absorption spectroscopy. This was first recognized by Pope et al. (1979), who showed that the spectrum of the photophoretic force on a 10 foa diameter perylene crystallite agrees with the optical spectrum. This was accomplished by suspending a perylene particle in a Millikan chamber with electro-optic feedback control and measuring the photophoretic force as a function of the wavelength of the laser illumination. Improvements on the technique and additional data were obtained by Arnold and Amani (1980), and Arnold et al. (1980) provided further details of their photophoretic spectrometer. A photophoretic spectrum of a crystallite of cadmium sulfide reported by Arnold and Amani is presented in Fig. 11. 

Minoura H, Tsuiki M (1978) Anodic reaction of several reducing agents on illuminated cadmium sulfide electrode. Electrochim Acta 23 1377-1382... 

Studies of the radiation emitted by a metallic vapor when it is illuminated by radiation from a cooled arc of that metal have been made for mercury by Wood, Fuchtbauer and others and for mercury, cadmium, lead, bismuth and thallium by Terenin. These results serve either as a verification of the Bohr energy level scheme of an atom or as a means for identification of certain energy levels in an atom whose series relations are unknown. 

KC1, which bathed the CdS film. This system was also investigated by cyclic voltammetry both in the dark and under illumination. Starting at about — 0.9 V, the dark cathodic current exhibited a peak at — 1.15 V due to Cd2+ reduction and then rose to — 1.4 V as a result of hydrogen production. The observed anodic peak at — 0.85 V was attributed to the stripping of cadmium deposits in the lattice (Cd ). Cyclic voltammetry subsequent to illumination resulted in the appearance of cathodic waves at — 1.0 V and — 1.3 V, at the expense of that at — 1.15 V. The anodic peak broadened, as is indicative of photocorrosion. 

In certain solids such as titanium dioxide or cadmium sulfide, the energy of the band gap corresponds to that of light (visible, ultraviolet, or infrared), with the result that the solid, when illuminated, may become electrically conducting or acquire potent chemical redox characteristics because of the promotion of electrons to the conduction band (which is normally unoccupied). These properties have obvious practical significance and are considered at length in Chapter 19. 

Analysis of Current-Voltage Characteristics of Illuminated Cadmium Selenide-Polysulfide Junctions... 

Acid (pH 3) ammonium oxalate has been widely used to dissolve iron and aluminium oxides and release bound trace metals since its introduction in 1922 (Tamm, 1922) (Tamm s reagent). Typically McLaren et al. (1986) used 0.17moll-1 ammonium oxalate +0.1 moll- 1 oxalic acid. The extraction is sensitive to light (Mitchell and Mackenzie, 1954) and particularly to ultraviolet light (Endredy, 1963). Schwertmann (1964) showed that in the dark the amorphous iron oxides were mainly attacked and under ultraviolet illumination the crystalline phases were dissolved as effectively as by the dithionite reagent. Heavy metals are released, with the exception of lead and cadmium whose oxalates are poorly soluble and which coprecipitate with calcium oxalate. The use of oxalic... 

Spanhel, L., H. Weller and A. Henglein (1987). Photochemistry of semiconductor colloids. 22. Electron ejection from illuminated cadmium sulfide into attached titanium and zinc oxide particles. Journal of the American Chemical Society, 109, 6632-6635. 

A major use of selenium has been in photoelectric devices. Its conductivity increases with illumination, and this provides a way of measuring light intensity or operating electrical switches. However, newer types of photocells are available that are made of other materials (such as cadmium sulfide). A second and more important use of selenium is in rectifiers to convert alternating current to direct current. Also, some pigments contain selenium and tellurium compounds, and both elements have been used in vulcanization of rubber. Selenium compounds have been used in dandruff treatment shampoos, and low levels of selenium may be necessary for dietary balance. Some studies have shown that persons whose diets are deficient in selenium may have a higher incidence of heart attacks. 

The three basic types are photoconductive, photovoltaic, and photo-emissive, and all are sensitive to both heat and light. The resistance of a photoconductive cell is lowered when it is illuminated and, over a small range, its response is linear. Cells containing lead sulfide, which is sensitive at wavelengths greater than 700 nm, and cadmium sulfide or selenide, with a sharp response maximum at 710 nm, have been used but may not give a stable response and are largely restricted to specialized applications in other fields. Silicon photodiodes and transistors are sensitive from 340 to 1200 nm with a peak at 900 nm. 

In the case of CdTe solar cells, CBD CdS is used in combination with electro-deposited [14, 238] or coevaporated CdTe [13, 32]. The process used for evaporated CdTe cells is based on an ammonia bath and has been described in detail [32]. An interesting point is that it seems that it is possible to control the doping of as grown CdS by introducing borate ions in the solution (boron is an n-type dopant in substitution of cadmium atoms). Resistivities of 10 Q - cm in dark and 2 Q cm under illumination were measured. Note that in this process the CdTe layer is deposited at... 

As reported in [125, 127], cadmium sulfide semiconductor wafers have been used as such a surface the conductance of these wafers was varied by exposure to light. The least adhesion was found for the surface that had been illuminated (Fig. IV.3, curve 3). The adhesion interaction correlates with the electrical resistance of the CdS wafer. When the wafer was protected from light, this resistance was 7 10 f2 after brief exposure to light it was 3 10 f2, and after extended exposure it dropped off to 5 10 The work function drops off upon illumination since the surface conductance increases and the resistance drops off. The increase in work function of the CdS brings about an equivalent decrease in adhesion (Fig. IV.3). 

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