Band-gap-narrowed semiconductors

Visible light absorption and charge separation using band-gap-narrowed semiconductor (BGNSC) materials that are stable in an oxidizing, aqueous solution environment and suitable for use as a photoanode. 

Visible Light Absorption and Charge Separation Using Band-Gap-Narrowed Semiconductors... 

Class C Quantum Supralattices. Another intriguing series of sodalites, that for the first time permits the investigation of narrow band gap monodispersed semiconductor QD s embedded in a wide band-gap semiconductor QS composed of monodispersed QD s (Figure 1), can be synthesized according to the following recipe ... 

The potassium salts are the most soluble and other salts usually are precipitated by addition of the appropriate metal chloride to a solution of the corresponding potassium salt. The metaniobates, MNbO, and orthoniobates, MNbO, generally are prepared by fusion of the anhydrous mixed oxides. The metaniobates crystallize with the perovskite stmeture and are ferroelectric (131) (see Ferroelectrics). The orthoniobates are narrow band-gap semiconductors (qv) (132). 

Heterogeneous Photocatalysis. Heterogeneous photocatalysis is a technology based on the irradiation of a semiconductor (SC) photocatalyst, for example, titanium dioxide [13463-67-7] Ti02, zinc oxide [1314-13-2] ZnO, or cadmium sulfide [1306-23-6] CdS. Semiconductor materials have electrical conductivity properties between those of metals and insulators, and have narrow energy gaps (band gap) between the filled valence band and the conduction band (see Electronic materials Semiconductors). 

Extensions in wavelength, into both the infrared and the ultraviolet ranges will continue, motivated by increasing interest in narrow band-gap semiconductors and wide band-gap materials. 

As an example, PL can be used to precisely measure the alloy composition xof a number of direct-gap III-V semiconductor compounds such as Alj Gai j, Inj Gai jfAs, and GaAsjfPj j(, since the band gap is directly related to x. This is possible in extremely thin layers that would be difficult to measure by other techniques. A calibration curve of composition versus band gap is used for quantification. Cooling the sample to cryogenic temperatures can narrow the peaks and enhance the precision. A precision of 1 meV in bandgap peak position corresponds to a value of 0.001 for xin AljfGai j, which may be usefiil for comparative purposes even if it exceeds the accuracy of the x-versus-bandgap calibration. 

Since the discovery of carbon nanotubes (CNTs) in 1991 [I], the band structures for CNTs have been calculated by a number of authors [2-7], They have predicted that CNTs can be metallic, narrow- or broad band-gap semiconductors. After macroscopic quantities of CNTs were synthesized [8], it has become possible to explore their practical properties. 

Organic dyes, aside from their role as sensitization agents for wide band gap semiconductors have been employed also for stabilization of narrow band gap semiconductors. The majority of such studies have considered metal or metal-free phthalocyanine films for both sensitization and electrode protection purposes [35]. 

Yet another approach to sensitizing PCs to a broader light spectrum is to use composite materials with a heterojunction (Fig. 6) between a narrow band gap and wide band gap semiconductors. A particular... 

The valence band top of d° or d10 stable oxide semiconductor with good photo-catalytic activity consists of an O 2p orbital. Commonly, the electrochemical potential of this VB is 2.5-3.5 V vs. NHE, which is considerably more positive than the redox potential of the O2/H2O redox couple. Strategies to narrow the band gap of these oxides and better match the redox potentials are ... 

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