Semiconductors cadmium compounds

Uses. The metal is used in electroplating, in solder for aluminum, as a constituent of easily fusible alloys, as a deoxidizer in nickel plating, in process engraving, in cadmium-nickel batteries, and in reactor control rods. Cadmium compounds are employed as TV phosphors, as pigments in glazes and enamels, in dyeing and printing, and in semiconductors and rectifiers. 

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... 

Simple cadmium compounds find application in many areas and the other chapters of this volume should be consulted. The more important of these uses appear to be as semiconductors and in various forms of colorizing agents. 

Second order non-linear optical properties have been reported for a variety of TTF donor-acceptor compounds <02T7463> and the palladium complex 84 is a room-temperature semiconductor <02CL936>. Preparation of the zinc and cadmium compounds 85 has been reported <02CC1474> and aromatic fused TTFs such as 86 form thin films with useful electrical properties <02JAP265466>. A ferromagnetic interaction occurs in the salt of a TTF... 

CdSe is a compound II-VI semiconductor composed of Cd + and Se ions. In the original synthetic procedure described by the Bawendi group, dimethyl cadmium [(Me)2Cd] and tri-n-octylphosphine selenide (TOPSe) were used as the precursors for Cd and Se, respectively. Later, other cadmium compounds such as cadmium acetate [Cd(Ac)2] and CdO were used alternatively, because (Me)2Cd is extremely toxic and pyrophoric. Although the exact reaction pathway has not been clearly elucidated, it is thought that atoms of Cd and Se are released via the thermal decomposition of the precursors. 

Quantum dots (QDs) are nanosized semiconductor particles of group II-VI or III-V main group elements with diameters of less than 10 nm [123]. These were first characterized in 1983 by Brus [124] as small semiconductor spheres in a colloidal suspension. QDs due to their nanoscale dimensions are subject to strong quantum confinement, which results in unique optical properties. Thus, in the last two decades, synthesis of QDs has attracted a lot of attention and generated a large number of publications [125]. A variety of methods have been proposed and implemented for synthesis of QDs. Of these methods, colloidal synthesis is the most accessible method for producing QDs suspended in solution. Colloidal synthesis of CdSe QDs is shown in Fig. 4. A cadmium compound is heated to 320°C... 

Materials like the cadmium compounds of sulfur, selenium, and tellurium, which are, respectively, yellow, red, and black, exhibit color by a mechanism we have not examined previously. Since cadmium has a d ° electronic configuration, crystal field splitting cannot be the origin of the color, but the color can be explained with recourse to a look at semiconductor properties. 

Mercury Telluride. Compounds of mercury with tellurium have gained importance as semiconductors with appHcations in infrared detection (9) and solar cells (10). The ratio of the components is varied, and other elements such as cadmium, zinc, and indium are added to modify the electronic characteristics. 

The intermetallic compounds with Group 16 (VIA) elements including CdS, CdSe, and CdTe have interesting semiconductor properties for photoconductors, photovoltaic cells, and ir windows. Cadmium sulfide is widely used as a phosphor in television tubes. 

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. 

Generally, the experimental results on electrodeposition of CdS in acidic solutions of thiosulfate have implied that CdS growth does not involve underpotential deposition of the less noble element (Cd), as would be required by the theoretical treatments of compound semiconductor electrodeposition. Hence, a fundamental difference exists between CdS and the other two cadmium chalcogenides, CdSe and CdTe, for which the UPD model has been fairly successful. Besides, in the present case, colloidal sulfur is generated in the bulk of solution, giving rise to homogeneous precipitation of CdS in the vessel, so that it is quite difficult to obtain a film with an ordered structure. The same is true for the common chemical bath CdS deposition methods. 

Dale PJ, SamantiUeke AP, Shivagan DD, Peter LM (2007) Synthesis of cadmium and zinc semiconductor compounds from an ionic liquid containing chohne chloride and urea. Thin Sohd Films 515 5751-5754... 

The next five chapters deal with deposition of specific groups of semiconductors. In Chapter 4, II-VI Semiconductors, all the sulphides, selenides, and (what little there is on) tellurides of cadmium (most of the chapter), zinc (a substantial part), and mercury (a small part). (Oxides are left to a later chapter.) This chapter is, understandably, a large one, due mainly to the large amount of work carried out on CdS and to a lesser extent on CdSe. Chapter 5, PbS and PbSe, provides a separate forum for PbS and PbSe, which provided much of the focus for CD in earlier years. The remaining sulphides and selenides are covered in Chapter 6, Other Sulphides and Selenides. There are many of these compounds, thus, this is a correspondingly large chapter. Chapter 7, Oxides and Other Semiconductors, is devoted mainly to oxides and some hydroxides, as well as to miscellaneous semiconductors that have only been scantily studied (elemental selenium and silver halides). These previous chapters have been limited to binary semiconductors, made up of two elements (with the exception of elemental Se). Chapter 8, Ternary Semiconductors, extends this list to semiconductors composed of three elements, whether two different metals (most of the studies) or two different chalcogens. 

Consequently, the bond is fully saturated for A sp = 0 with a bond order of 1, but it is only partially saturated by the time the gap closes for AEap/2 h = 1 (cf eqn (7.92)) when the bond order equals 0.76. This simple second moment model has been extended to include the compound semiconductors. The resultant values of the bond order are given in Table 7.2. We see that the bonds in tetrahedral carbon and silicon are almost fully saturated, but those in zinc selenide and cadmium telluride are only about 75% saturated due partly to the mismatch in the sp orbitals between chemically distinct atoms. 

The actions of photoexcited semiconductor particles on organic compounds under oxygen is of significant importance from both practical and basic aspects. Semiconductors like titanium dioxide and cadmium sulfide were shown to induce oxidation of olefins and aromatic hydrocarbons under oxygen, and also to sensitize isomerization of unsaturated systems. The mechanisms of these reactions are discussed. 

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