Cadmium sulfide deposition

Cadmium Sulfide Photoconductor. CdS photoconductive films are prepared by both evaporation of bulk CdS and settHng of fine CdS powder from aqueous or organic suspension foUowed by sintering (60,61). The evaporated CdS is deposited to a thickness from 100 to 600 nm on ceramic substates. The evaporated films are polycrystaUine and are heated to 250°C in oxygen at low pressure to increase photosensitivity. Copper or silver may be diffused into the films to lower the resistivity and reduce contact rectification and noise. The copper acceptor energy level is within 0.1 eV of the valence band edge. Sulfide vacancies produce donor levels and cadmium vacancies produce deep acceptor levels. 

Copper Sulfide—Cadmium Sulfide. This thin-film solar cell was used in early aerospace experiments dating back to 1955. The Cu S band gap is ca 1.2 eV. Various methods of fabricating thin-film solar cells from Cu S/CdS materials exist. The most common method is based on a simple process of serially overcoating a metal substrate, eg, copper (16). The substrate first is coated with zinc which serves as an ohmic contact between the copper and a 30-p.m thick, vapor-deposited layer of polycrystaUine CdS. A layer is then formed on the CdS base by dipping the unit into hot cuprous chloride, followed by heat-treating it in air. A heterojunction then exists between the CdS and Cu S layers. 

Cadmium is an extremely toxic metal that finds its way into the aqueous environment as a result of some human activities. A major cause of cadmium pollution is zinc mining and processing, because natural deposits of ZnS ores usually also contain CdS. During the processing of these ores, highly insoluble cadmium sulfide ( sp = 7.9 X 10 ) maybe converted into considerably less insoluble cadmium hydroxide (.E p — 7.2 X 10" ). What mass of Cd (OH)2 will dissolve in l.OOx lO L of an aqueous solution ... 

Rieke PC, Bentjen SB (1992) Deposition of cadmium sulfide films by decomposition of thiourea in basic solutions. Chem Mater 5 43-53... 

Lincot D, Ortega-Borges R (1992) Chemical bath deposition of cadmium sulfide thin films. In situ growth and structural studies by Combined Quartz Crystal Microbalance and Electrochemical Impedance techniques. J Electrochem Soc 139 1880-1889... 

Ortega-Borges R, Lincot D (1993) Mechanism of chemical bath deposition of cadmium sulfide thin films in the ammonia-thiourea system. J Electrochem Soc 140 3464-3473... 

Let us add here that the fabrication of polycrystalline semiconductive films with enhanced photoresponse and increased resistance to electrochemical corrosion has been attempted by introducing semiconductor particles of colloidal dimensions to bulk deposited films, following the well-developed practice of producing composite metal and alloy deposits with improved thermal, mechanical, or anti-corrosion properties. Eor instance, it has been reported that colloidal cadmium sulfide [105] or mercuric sulfide [106] inclusions significanfly improve photoactivity and corrosion resistance of electrodeposited cadmium selenide. 

Rufus IB, Viswanathan B, Ramakrishnan V, Kuriacose JC (1995) Cadmium sulfide with iridium sulfide and platinum sulfide deposits as a photocatalyst for the decomposition of aqueous sulfide. J Photochem Photobiol A 91 63-66... 

Meth, J. S. Zane, S. G. Sharp, K. G. Agrawal, S. 2003. Patterned thin film transistors incorporating chemical bath deposited cadmium sulfide as the active layer. Thin Solid Films. 444 227-234. 

Kitaev, G. A. Uritskaya,A. A. Moksushin, S. G. 1965. Conditions for the chemical deposition of thin films of cadmium sulfide on a solid surface. Russ. J. Phys. Chem. 39 1101-1102. 

Popescu, V. Pica, E. M. Pop, I. Grecu, R. 1999. Optical properties of cadmium sulfide thin films, chemically deposited from baths containing surfactants. Thin... 

O Brien, R McAleese, J. 1998. Deposition and characterization of cadmium sulfide thin films by chemical bath deposition. /. Mater. Chem. 8 2309-2314. 

UPD Cd can also be used to obtain cadmium sulfide, an important semiconductor for electronics. Electrochemical epitaxial growth of organized CdS structures, involving underpotentially deposited Cd on Au(lll) was thus reported [161, 265]. 

Cadmium sulfide [68859-25-6], CdS, Mr 144.48, occurs as greenockite or cadmium-blende in several natural deposits, which are, however, of no importance as pigments. The mineral crystallizes hexagonally in the wurtzite lattice (a-form). 

H.-J. Klimisch, C. Gembardt, H.-P. Gelbke Lung Deposition and Clearance, Lung Pathology and Renal Accumulation of Inhaled Cadmium Chloride and Cadmium Sulfide in Rat, BASF, Ludwigshafen 1991. 

Colloids of semiconductors are also quite interesting for the transmembrane PET, as they possess both the properties of photosensitizers and electron conductors. Fendler and co-workers [246-250] have shown that it is possible to fix the cadmium sulfide colloid particles onto the membranes of surfactant vesicles and have investigated the photochemical and photocatalytic reactions of the fixed CdS in the presence of various electron donors and acceptors. Note, that there is no vectorial transmembrane PET in these systems. The vesicle serves only as the carrier of CdS particles which are selectively fixed either on the inner or on the outer vesicle surface and are partly embedded into the membrane. However, the size of the CdS particle is 20-50 A, i.e. this particle can perhaps span across the notable part of the membrane wall. Therefore it seems attractive to use the photoconductivity of CdS for the transmembrane PET. Recently Tricot and Manassen [86] have reported the observation of PET across CdS-containing membranes (see System 32 of Table 1), but the mechanism of this process has not been elucidated. Note, that metal sulfide semiconductor photosensitizers can be deposited also onto planar BLMs [251],... 

Investigations by Malinowska et al. [110] have shown that absorption can be used to recover 90% of ammonia that is vaporized during chemical bath deposition of cadmium sulfide thin layers from which concentrated solutions with more than lOmolL-1 of pure ammonia can be obtained. Additionally, a cake with mixed cadmium sulfide-cadmium cyanamide is produced, from which cadmium can be recovered hydrochemically as cadmium sulfate [111]. The global process recovers up to 99.999% of cadmium and generates only solid sulfur and a liquid effluent containing traces of cadmium. 

According to the foregoing interpretation, chrysocolla of ancient times is neither malachite nor a blue copper silicate (the mineral now called chrysocolla) but is a yellow substance, possibly the yellow mineral cadmium sulfide, which appears as a coating on other minerals, chiefly zinc sulfide. This description fits Pliny s text, which describes gold solder (chrysocolla) as a liquid that flows from several mines to give a solid deposit. ... 

The basic structure of polycrystalline cadmium telluride (CdTe) thin-film cells has a glass superstrate and a layer of TCO as front contact, a near-transparent n-type cadmium sulfide (CdS) window layer, p-type CdTe, and a metallic rear contact. The CdTe is usually deposited by three families of techniques. In the first group (vapor transport deposition, close space sublimation, physical vapor deposition, and sputtering) elemental vapors of Cd and Te condense and react on the substrate. In the second (electrodeposition), Cd + and HTe02" ions in acidic electrolyte are galvanically reduced at the surface ... 

Due to the presence of the ionic P4VP-Re-complex block on the film surface, nanoparticles decorated with anionic functional groups can be deposited on the copolymer film surface by electrostatic attraction. The copolymer film was immersed into a solution of cadmium sulfide nanoparticles (diameter = 10 nm), functionalized with carboxylate groups on the particle surface. The attachment of cadmium sulfide nanoparticles on the film surface was confirmed by X-ray photoelectron spectroscopy (XPS). In addition, particles deposited on the cylindrical blocks in the copolymer film surface were also observed in AFM image (Figure 5.12). This approach has potential in fabricating nanoparticle-polymer composites on patterned surface. 

Figure 5.12 AFM image of PS-h-P4VP-[Re(DIAN)(C0)3]+C10F deposited with cadmium sulfide nanoparticles. (From Cheng and Chan.71 Reprinted with permission. Copyright 2005 American Chemical Society.)...

Mixed alkyl/dithio- or diselenocarbamates are potential precursors to II-VI materials as they provide access to lower deposition temperatures. Zinc selenide, cadmium sulfide, and cadmium selenide thin films have been deposited from compounds of the type [RM(E2CNEt2)]2 (79, M = Zn, E = S, R = Me 80, M = Cd, E = S, R = Me 81, M = Cd, E = Se, R = Me 82, M = Cd, E = S, R = CH2CMe3 83, M = Cd, E = Se, R = CH2CMe3). The films were superior and higher growth rates were obtained as compared with those... 

Lead sulfide transducers arc sensitive in the region between 0.8 and 3 pm (12,500 to 3300 cm ). A thin layer of this eompound is deposited on glass or quartz plates to form (he cell. The cm ire assembly is then sealed in an evacuated container to protect the semiconductor from reaction with the atmosphere. The sensitivity of cadmium sulfide, cadmium seicnide.and lead sulfide transducers is shown by curves B. D, and O in Figure 7-27,... 

The wet synthesis of CdS nanoparticles used in this work is based on the reaction between a dissolved cadmium salt (CdCl2) and a S-containing compound (thiourea (NH2)2CS) in an aqueous solution. Chemical deposition of CdS nanoparticles in the CdCl2 - NH3 - NaOH - (NH2)2CS - H2O bath was described elsewhere [3]. In the present work all the baths had the same composition and were prepared from solutions of cadmium chloride CdCl2 (0.005 mold-1), ammonia NH3-H2O (1.5 moll"1), sodium hydroxide NaOH (0.074 mold-1) and thiourea (NH2)2CS (0.025 mol-F1) using distilled water. The synthesis temperature was varied from 294 to 325 K. The primary concentrations of the precursors have been chosen according to the thermodynamic analysis [4]. A supersaturation of the solution with Cd(OH)2 takes place in the baths. It means that the mechanism of the cadmium sulfide formation could involve the stage of Cd(OH)2 formation. When the deposition process of CdS particles in the solution completed, the residue was filtered at an ambient pressure and dried at room temperature. 

As indicated above for cadmium sulfides and selenides, CBD is a well-known deposition process for some other chalcogenides such as sulfides and selenides of Zn, In, Co, Hg, Pb, Sb2S3 and Sb2Bi2 S3 [231]. The deposition of metal cholcoge-nide films is based of following properties of thiosulfate/selenosulfate [232]. 

Poly(p-xylylene)-cadmium sulfide nanocomposites were synthesized using the vapor deposition polymerization in an inhomogeneous electric field [103]. There, a gradient of concentration and size of the cadmium sulfide nanoparticles along the direction of the applied electric field emerge. 

Dimethylcadmium forms an 1 1 adduct with dioxane which is used in metal-organic chemical vapor deposition of cadmium sulfide. This material is a self-organized monodimensional array, 23, formed via O Cd bonds (2.88 and 2.75 A). The coordination geometry around cadmium is rather curious the methyl groups are arranged linearly (C-Cd-C 173.0°), other angles being as follows O-Cd-0 114.2°, C-Cd-O 88.8° and 93.5°. Some association between dimethylcadmium and dioxane is also maintained in benzene solution [44]. 

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