Cadmium-zinc-tellurium

A p-type layer 18 and an n-type layer 20 of HgCdTe are grown epitaxially on a substrate 52 of cadmium zinc tellurium. A set of through holes are formed which extend through the layers 18 and 20 up to the surface of the substrate. A silicon dioxide layer is applied and at each detector a window is etched. A contact metal 24A is applied within each window. Contacts 24 and 26 are constructed on the detectors and on the read-out chip 14. The chip and the substrate 52 are pushed together to compress the contacts 24 and 26 against each other which cold welds them to each other. 

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. 

Production and Economic Aspects. Thallium is obtained commercially as a by-product in the roasting of zinc, copper, and lead ores. The thallium is collected in the flue dust in the form of oxide or sulfate with other by-product metals, eg, cadmium, indium, germanium, selenium, and tellurium. The thallium content of the flue dust is low and further enrichment steps are required. If the thallium compounds present are soluble, ie, as oxides or sulfates, direct leaching with water or dilute acid separates them from the other insoluble metals. Otherwise, the thallium compound is solubilized with oxidizing roasts, by sulfatization, or by treatment with alkaU. The thallium precipitates from these solutions as thaUium(I) chloride [7791 -12-0]. Electrolysis of the thaUium(I) sulfate [7446-18-6] solution affords thallium metal in high purity (5,6). The sulfate solution must be acidified with sulfuric acid to avoid cathodic separation of zinc and anodic deposition of thaUium(III) oxide [1314-32-5]. The metal deposited on the cathode is removed, kneaded into lumps, and dried. It is then compressed into blocks, melted under hydrogen, and cast into sticks. 

Determination of copper as copper(I) thiocyanate Discussion. This is an excellent method, since most thiocyanates of other metals are soluble. Separation may thus be effected from bismuth, cadmium, arsenic, antimony, tin, iron, nickel, cobalt, manganese, and zinc. The addition of 2-3 g of tartaric acid is desirable for the prevention of hydrolysis when bismuth, antimony, or tin is present. Excessive amounts of ammonium salts or of the thiocyanate precipitant should be absent, as should also oxidising agents the solution should only be slightly acidic, since the solubility of the precipitate increases with decreasing pH. Lead, mercury, the precious metals, selenium, and tellurium interfere and contaminate the precipitate. 

The chalcogenides are binary compounds of a chalcogen (i.e., the elements of Group Ilb zinc, cadmium, mercury) with a less electropositive element, such as those of Group VIb (oxygen, sulfur, selenium, and tellurium). This section covers the sulfides, selenides, andtellurides. Oxides are reviewed above in Ch. 11. Most of the chalcogenides have useful optical characteristics and their applications are usually found in optics. 

Reaction on warming powdered cadmium with selenium or tellurium is exothermic, but less vigorous than that of zinc. 

Nickel and selenium interact with incandescence on gentle heating [1], as do also sodium and potassium, the latter mildly explosively [2], Uranium [3] and zinc [4] also incandesce when their mixtures with selenium are heated, and platinum sponge incandesces vividly [5], The particle size of cadmium and selenium must be below a critical size to prevent explosions during synthesis of cadmium selenide by heating the elements together. Similar considerations also apply to interaction of cadmium or zinc with sulfur, selenium or tellurium [6], Interaction of powdered tin and selenium at 350° C is extremely exothermic [7],... 

Zinc telluride, ZnTe, was deposited on quartz, silicon, InAs, and GaSb substrates using Zn[TeSi(SiMe3)3]2 at temperatures between 250 °C and 350 °C. On InAs (orientation not specified) a cubic ZnTe layer was obtained. Problems of stoichiometry are encountered at temperatures below 325 °C because decomposition of the precursor is incomplete, while at higher temperatures (above 350 °C) the deposited ZnTe decomposes into Zn (which evaporates) and involatile elemental tellurium which remains. The results with the analogous cadmium precursor (1.4 torr, 290 °C) indicate that the CdTe films may be of better stoichiometry than those of ZnTe, with XRD results indicating that on a Si substrate the hexagonal phase is predominantly... 

The structural chemistry of some metal dithiocarbamates, i.e. systematics, coordination modes, crystal packing, and supramolecular self-assembly patterns of nickel, zinc, cadmium, mercury,363 organotin,364 and tellurium,365 366 complexes has been thoroughly analyzed and discussed in detail. Supramolecular self-assembly frequently occurs in non-transition heavier soft metal dithiocarbamates. Thus, lead(II),367 bismuth(III)368 zinc,369 cadmium,370 and (organo)mercury371 dithiocarbamates are associated through M- S secondary bonds, to form either dimeric supermolecules or chain-like supramolecular arrays. The arsenic(III)372 and antimony(III)373 dithiocarbamates are... 

Antimony, arsenic, bismuth, cadmium, calcium, cesium, chromium, cobalt, copper, gold, indium, iridium, iron, lead, lithium, magnesium, manganese, mercury, nickel, palladium, platinum, potassium, rhodium, rubidium, ruthenium, selenium, silver, sodium, tellurium, thallium, zinc... 

Tellurium forms many sulfides and oxysulfides. The metal reacts with sulfides of zinc, cadmium, or mercury, forming tellurium sulfide ... 

The first ALD thin films were deposited in the 1970s using elemental zinc and sulphur, reacting to form ZnS at 250-450 °C [44], Although metals as ALD precursors seems to be the most straightforward method of producing compound thin films, this type of process is limited by the generally low vapour pressure of elemental metals. Therefore only zinc and cadmium have been used as metal sources in ALD processes. However, some metalloids, e.g. selenium and tellurium, can be used as well. 

Aqueous solutions of the salts, or of tellurium dioxide in acids, easily undergo reduction.to elementary tellurium. Phosphorus, phosphorous acid,-7 hypophosphorous acid,8 sulphurous acid,9 thiosulphuric acid,10 hyposulphurous acid,11 hydriodic acid,12 hydrogen sulphide,13 ferrous salts, stannous salts,14 hydrazine 15 and phenylhydrazine, as well as various metals,18 e.g. zinc, iron, tin, cadmium, antimony and copper, are able to effect this reduction. 

On the basis of chemical profile, Wood (38) predicted that arsenic, selenium, and tellurium will be methylated in the environment, and lead, cadmium, and zinc will not. Elemental concentration in the aquatic food chain has been reported for As (39), Hg (40), Cd (41), Pb (42), and Cu (43). The biological half-life of methylmercury in fish, for example, is one to two years (44). Pillay et al. (40) implicated heavy coal burning in the mercurial contamination of plankton and fish populations of Lake Erie. Other metals, notably cadmium, have been shown to be incorporated into the grazing grasses surrounding a coal burning source (27). Trace element contamination, therefore, can enter the food chain at various points. Disposal of solid wastes in the form of ash and slag is yet another environmental consideration (45). 

Industrial specifications normally require that impurities in cadmium metal not exceed the following zinc, 0.035% copper. 0.015% lead. 0.025% tin, 0.01% silver. 0.01 % antimony, 0.001% arsenic. 0.003% and tellurium. 0.003%. The metal Is available in numerous Tornis, Eleclroplaters generally prefer balls 2 inches (5 centimeters) in diameter. 

Van Vleet JF, Boon GD, Ferrans VJ. 1981. Induction of lesions of selenium-vitamin E deficiency in ducklings fed silver, copper, cobalt, tellurium, cadmium, or zinc Protection by selenium. Am J Vet Res 42 1206-1217. 

From the late 1960s onwards, a number of research groups around the world began to investigate alternatives to pneumatic nebulization for sample introduction, in an attempt to overcome transport efficiency limitations. The most successful approaches were those which involved heating small, discrete liquid samples, and sometimes even solid samples, directly on a metal filament, boat, or cup which could be positioned reproducibly into a flame. However, since the temperature of the metal would be lower than that of the flame itself, the techniques were confined to the determination of relatively easily atomized elements such as arsenic, bismuth, cadmium, copper, mercury, lead, selenium, silver, tellurium, thallium, and zinc. 

---