Semiconductor/semiconductivity synthesis

It is possible that colloidal photochemistry will provide a new approach to prebiotic syntheses. The work described previously on redox reactions at colloidal ZnS semiconductor particles has been carried on successfully by S. T. Martin and co-workers, who studied reduction of CO2 to formate under UV irradiation in the aqueous phase. ZnS acts as a photocatalyst in the presence of a sulphur hole scavenger oxidation of formate to CO2 occurs in the absence of a hole scavenger. The quantum efficiency for the formate synthesis is 10% at pH 6.3 acetate and propionate were also formed. The authors assume that the primeval ocean contained semiconducting particles, at the surface of which photochemical syntheses could take place (Zhang et al 2007). 

Sometimes, semiconductivity depends on the type of a structural phase that arises from synthesis. Thus, in the case of (TCNQ) Cu the semiconducting phase is thermodynamically disfavored. To prepare this semiconductor, Harris et al. (2005) proposed to perform the reduction of TCNQ in acetonitrile at glass-carbon, gold, or platinum electrode in the presence of Cu. This allows the electrocrystallization of sparingly soluble TCNQCu semiconducting phase to occur by a nucleation... 

Since the first synthesis of mesoporous materials MCM-41 at Mobile Coporation,1 most work carried out in this area has focused on the preparation, characterization and applications of silica-based compounds. Recently, the synthesis of metal oxide-based mesostructured materials has attracted research attention due to their catalytic, electric, magnetic and optical properties.2 5 Although metal sulfides have found widespread applications as semiconductors, electro-optical materials and catalysts, to just name a few, only a few attempts have been reported on the synthesis of metal sulfide-based mesostructured materials. Thus far, mesostructured tin sulfides have proven to be most synthetically accessible in aqueous solution at ambient temperatures.6-7 Physical property studies showed that such materials may have potential to be used as semiconducting liquid crystals in electro-optical displays and chemical sensing applications. In addition, mesostructured thiogermanates8-10 and zinc sulfide with textured mesoporosity after surfactant removal11 have been prepared under hydrothermal conditions. 

From the perspective of a materials scientist, tellurium is certainly the most attractive element, and it has found applications mainly in the electronics industry because of its p-type semiconducting properties. It can also be used for the synthesis of so-called II-VI semiconductors (such as MgTe) or may be alloyed to yield superior intermetallic phases. In addition, some Te alloys are under investigation in the realm of phase-change media for rapid data storage [273]. 

The conclusions set out in Table 2 are based on Verwey s mechanism and supported by examples from various sources. We shall consider only those conclusions which are useful in the synthesis of semiconductors. The proportions represented by the cation-anion ratio must be obeyed strictly in the doping of a semiconducting compound and, therefore, an excess of one of the components must be added, in addition to the dopant. The essence of Verwey s mechanism must be understood correctly. For example, an attempt to prepare p-lype HgSe by adding pure silver is reported in [34]. When we consider this case, it becomes clear why the expected p-type conduction is not obtained and, in fact, the n-type conduction is enhanced. K follows from the reaction... 

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