Cadmium chalcogenide

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. 

Complex equilibria among multiple species are typical also of polyselenide and polytelluride solutions. Aqueous polyselenide solutions have been employed as electrolytes in high-elRciency PEC with photoanodes made of gallium arsenide and cadmium chalcogenides (Chap. 5). Unlike polysulfides, the fundamental equilibria constraining the distribution of polyselenide species have not been meticulously characterized [19]. 

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. 

Bouroushian M, Loizos Z, Spyrellis N, Mamin G (1997) Hexagonal cadmium chalcogenide thin films prepared by electrodeposition from near-boihng aqueous solutions. Appl Surf Sci 115 103-110... 

Klein JD, Herrick RD, Palmer D, Sailor Ml, BrumUk CJ, Martin CR (1993) Electrochemical fabrication of cadmium chalcogenide microdiode arrays. Chem Mater 5 902-904... 

Rauh RD (1988) Cadmium Chalcogenides (CdS, CdSe, CdTe). In Finklea HO (ed) Semiconductor Electrodes (Studies in Physical and Theoretical Chemistry 55) Elsevier... 

Elhs AB, Kaiser SW, Bolts JM, Wrighton MS (1977) Study of n-type semiconducting cadmium chalcogenide-based photoelectrochemical cells employing polychalcogenide electrolytes. J Am Chem Soc 99 2839-2848... 

Hodes G, Manassen J, Neagu S, Cahen D, Mirovski Y (1982) Electroplated cadmium chalcogenide layers Characterization and use in photoelectrochemical solar cells. Thin Solid Films 90 433-438... 

Although direct synthesis of cadmium chalcogenide quantum dots in the aqueous phase was achieved nearly 30 years ago, the synthesis of size-controlled CdSe quantum dots in the aqueous phase became possible only recently. Rogach et al. successfully synthesized CdSe quantum dots in the aqueous phase from a mixture of cadmium perchlorate (4.7 mmol), sodium hydroselenide (2.2 mmol), and 2-mercaptoethanol or 1-thioglycerol (11.54mmol) [15]. In a typical synthesis, the above mixture was refluxed in an aqueous NaOH solution (pH = 11.2) in a N2... 

The first deposition experiments using SILAR were performed to grow zinc and cadmium chalcogenide films.1 Metal salt solutions and sodium sulfide were used as precursors in most experiments. Table 8.2 provides a more complete... 

Cadmium chalcogenide thin hlms have been grown by ECALE using cadmium sulphate as metal source and sodium sulphide, sodium selenite,... 

Stability of Cadmium-Chalcogenide-Based Photoelectrochemical Cells... 

A major concern for the use of these quantum dots in liquid crystal applications is their stability. Weller et al. using NMR spectroscopy, UV-vis spectrophotometry, and analytical ultracentrifugation (AUC) showed that thiol-stabilized cadmium chalcogenide quantum dots are unstable at low particle concentrations (<10 pM in DMF), i.e., even the covalently bound thiols desorb from the quantum dot surface... 

NCs is indispensable. In the case of cadmium chalcogenide NCs, the concentration of a colloidal solution can be determined in good approximation by means of UV-vis absorption spectroscopy thanks to tabulated relationships between the excitonic peak, the NC size, and the molar absorption coefficient.96 An advanced approach for shell growth derived from chemical bath deposition techniques and aiming at the precise control of the shell thickness is the so-called SILAR (successive ion layer adsorption and reaction) method.97 It is based on the formation of one monolayer at a time by alternating the injections of cationic and anionic precursors and has been applied first for the synthesis of CdSe/CdS CS NCs. Monodispersity of the samples was maintained for CdS shell thicknesses of up to five monolayers on 3.5 nm core CdSe NCs, as reflected by the narrow PL linewidths obtained in the range of 23 to 26 nm FWHM. 

ZnO and CdO are wide bandgap semiconductors, and these materials may serve as transparent conducting oxides for photovoltaics and flat panel displays. ZnO may also have applications in blue and ultraviolet fight emitting devices and laser diodes. Thin films of zinc and cadmium chalcogenides also have many potential applications. The technological goals of these materials have been smnmarized in several recent... 

Metal microtubules were prepared in a similar marmer, with lower internal diameters of 0.8 nm, and the authors could demonstrate that ion transport through such tubules can be switched from positive to negative ions with external potentials applied to the membrane. 2 Gold nanowires (of as little as 10 nm diameter) deposited in nanoporous filtration disks can also act as nanoelectrodes with sensitive cyclic voltammetric detection limits. Finally, the template membrane approach has also been extended to arrays of cadmium chalcogenide phases. Thus, 200 nm-diameter CdSe or graded CdSe/CdTe cylinders were electrodeposited in the pores of Anopore membranes. A Ni-CdSe array was found to be rectifying.i ... 

McHale JM, Auroux A, Perrotta AJ, Navrotsky A (1997) Surface energies and thermodynamic phase stability in nanocrystalline aluminas. Science 277 788-791 Molteni C, Martonak R, Parrinello M (2001) First principles molecular dynamics simulations of pressure-induced stiuctural transformations in silicon clusters. J Chem Phys 114 5358-5365 Murray CB, Norris DJ, Bawendi MG (1993) Synthesis and characterization of nearly monodisperse CdE (E = S, Se, Te) semiconductor nanocrystallites. J Am Chem Soc 115 8706-8715 Onodera A (1972) Kinetics of polymorphic transitions of cadmium chalcogenides under high pressure. Rev Phys Chem Japan 41 1... 

Ternary compounds (not alloys) such as CdCr2Sc4 can be grown from a PbCl2-CdCl2 flux. These are magnetic semiconductors, but they have been eclipsed by the manganese- and iron-based alloys with zinc and cadmium chalcogenides, such as Cdi -,cMn,tTe. The pure compounds, usually made by direct reaction, are often used as... 

S.E. Dann and M.T. Weller, Synthesis and Structure of Cadmium Chalcogenide Beryllo-silicate Sodalites. Inorg. Chem., 1996, 35, 555-558. 

---