Semiconductor Composites

Recent considerations of metal UPD on semiconductor surfaces suggest that light-assisted processes gain much significance in the relevant technology. The use of photoinduced UPD as an approach for the preparation of compounds and composite semiconductors either in thin films (layered structures) or in particulate suspensions is a challenging issue that will be outlined promptly. 

Chenthamarakshan CR, Ming Y, Rajeshwar K (2000) Underpotential photocatalytic deposition A new preparative route to composite semiconductors. Chem Mater 12 3538-3540... 

Nasr C, Hotchandani S, Kim WY, Schmehl RH, Kamat PV (1997) Photoelectrochemistry of composite semiconductor thin films. Photosensitization of Sn02/CdS coupled nanocrystal-Utes with a ruthenium polypyridyl complex. J Phys Chem B 101 7480-7487... 

ZnS-CdS (bandgap = 2.3-2.4 eV) composite semiconductor photoelectrodes show a broad spectral response and n-type behavior, with saturation of the anodic photocurrent upon increasing anodic potential making the system suitable for use as a photoelectrochemical cell photoanode [72], Nanostructured ZnS-CdS thin film electrodes show that anodic photocurrent saturation can be attained with the application of a small, 0.1 V, bias [73], while hydrogen evolution is observed at the Pt cathode. The performance of the ZnS-CdS photoanodes appear strongly dependent upon the method of film preparation [72,73], with Zn rich films demonstrating superior photocurrent generation, and stability, in comparison to Cd rich films. 

Formation of composite and sandwich-type semiconductors constitutes an interesting development (Fig. 100) [576,605-609]. A composite semiconductor, like a cherry and its stone, contains one material as its core and a second material as its shell. CdS particles coated by Cd(OH)2, CdSe coated by ZnS, and HgS coated by CdS are examples of recently prepared composite semiconductors... 

The feasibility of synthesizing composite semiconductor nanoclusters by chemical precipitation or electrochemical deposition opens up a wide array of possi-... 

Composite semiconductor nanoclusters can be classified into two categories, namely, capped- and coupled-type heterostructures. The capped nanoclusters essentially have a core-shell geometry while in a coupled system two semiconductor nanoclusters are in contact with each other. The principle of charge separation in capped and coupled semiconductor systems is illustrated in Fig. 12. 

An interesting aspect of composite semiconductor nanoclusters is their ability to rectify the charge carrier flow following the bandgap excitation of the... 

Nasr, C. Hotchandani, S. Kamat, P. V. Photoelectrochemical behavior of composite semiconductor thin films and their sensitization with ruthenium polypyridyl complex. In Photoelectrochemistry, K. Rajeshwar, ed., The Electrochemical Society Pennington, NJ, 1997, in press. 

Kamat PV. Composite Semiconductor Nanoclusters. Studies in surface science and catalysis. Amsterdam Elsevier, 1996. 

Figure 7.17 Modes of Ti02 photosensitization (a) photosensitization with organic or inorganic chromophores chemisorbed onto titanium dioxide surface (b) formation of surface complexes exhibiting metal-to-band charge transfer transitions (MBCT) (c) bulk doping resulting in formation of acceptor or donor levels and (d) formation of composite semiconductors. A denotes the electron acceptor, D the electron donor...

Composite semiconductors Semiconductor mixing (composite) is another strategy for developing photocatalysts with visible-light response from photocatalysts with a wide band gap. This strategy is based on the coupling of a wide band-gap semiconductor with a narrow band semiconductor with... 

P. V. Kamat, Composite Semiconductor Nanoclusters, in Semiconductor Nanoclusters - Physical, Chemical and Catalytic Aspects., P. V. Kamat and D. Meisel, Editors. 1997, Elsevier Science Amsterdam, p. 237-259. 

Figure 11. Photo-induced charge separation in composite semiconductor particles (a) capped and (b) coupled semiconductor nanocrystallites. Photo-generated charge carriers move in opposite directions.

Fig. 2 (A) Schematic of SLS growth mechanism. M and E are elements of the composite semiconductor material. (B) TEM image of an InP whisker. The white arrow points at the In flux particle at the whisker s tip. (Erom Ref. l)...

Boron Boron, metallic EINECS 231-151-2 HSDB 4482. Nonmetallic element. Used in special-purpose alloys cementation of iron neutron absorber in reactor controls oxygen scavenger for copper and other metals fibers and filaments in composites semiconductors rocket propellant mixtures, mp = 2200" insoluble in H2O. Atomergic Chemetals Noah Chem. 

Chapters 12 and 13 cover two of the most important novel catalytic applications of carbon materials, electrocatalysis and photocatalysis. In the first case, carbons are used mostly as supports for metal catalysts in fuel cells, while the synergistic effects of carbon-based composite semiconductor materials, such as C-TiOi, make them particularly effective in photocatalytic degradation reactions. 

In this section some optical properties of composite semiconductor particles are reviewed. We shall restrict ourselves to aspects of surface modification of given particles and the formation of core-shell structures. We are leaving out of consideration the field of sandwich colloids (i.e., two different semiconductor particles attached to each other) since their properties have been reviewed in detail before [5,11,12]. 

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