Semiconductors colloids

Peng Z G, Wickham J and Alivisatos A P 1998 Kinetics of ll-VI and lll-V colloidal semiconductor nanocrystal growth focusing of size distributions J. Am. Chem. Soc. 120 5343... 

Peng, X. G. (2003). Mechanisms for the Shape-control and Shape-Evolution of Colloidal Semiconductor Nanocrystals. Adv. Mater., 15,459-463. 

An important aspect of semiconductor photochemistry is the retardation of the electron-hole recombination process through charge carrier trapping. Such phenomena are common in colloidal semiconductor particles and can greatly influence surface corrosion processes occurring particularly in small band gap materials, such... 

Kamat PV, Dimitrijevic NM (1990) Colloidal semiconductors as photocatalysts for solar energy conversion. Sol Energy 44 83-98... 

Duonghung D, Ramsden J, Gratzel M (1982) Dynamics of interfacial electron-transfer processes in colloidal semiconductor systems. J Am Chem Soc 104 2977-2985... 

Spanhel L, Haase M, Weller H, Henglein A (1987) Photochemistry of colloidal semiconductors. 20. Surface modification and stability of strong luminescing CdS particles. J Am Chem Soc109 5649-5655... 

Peng X, Wickham J, Ahvisatos AP (1998) Kinetics of 11-VI and III-V colloidal semiconductor nanocrystal growth Focusing of size distributions. J Am Chem Soc 120 5343-5344... 

With respect to using methyl viologen as electron relay, it might be of interest to note tlmt MV " can be oxidized by positive holes produced in illuminated colloidal semiconductors such as Ti02 Two oxidation products of MV are 1, 2 -di-hydro-l,r-dimethyl-2 -oxo-4,4 -bipyridylium chloride and 3,4-dihydro-l,r-dime-thyl-3-oxo-4,4 -bipyridylium chloride, which can readily be detected by their strong fluorescences at 516 nm and 528 nm, respectively. These products are also produced in the direct photolysis of MV " solutions and in the reaction of MV "" with OH radicals in homogeneous solution... 

The photoassisted reduction of C02 with suspended semiconductor powders gives, at present, very low energy efficiencies (at most, ca. 0.01% or less). The use of colloidal semiconductor particles is more efficient in some cases. 

Kamat, P.V., Interfacial charge transfer processes in colloidal semiconductor systems, Prog. React. Kinet., 19,277,1994. 

Colloidal semiconductor nanocrystals are attracting growing attention as the building blocks for inexpensive, large-area, solution-processed solar cells. The advantages here are the scalable and controlled synthesis, an ability to be processed in solution, the broadband absorption, and the superior transport properties of traditional photovoltaic semiconductors. Solar cells that rely exclusively on colloidal nanocrystals have been anticipated theoretically58 and... 

Vanmaekelbergh, D. Liljeroth, P. 2005. Electron-conducting quantum dot solids novel materials based on colloidal semiconductor nanocrystals. Chem. Soc. Rev. 34 299-312. 

Photoredox processes with colloidal semiconductor particles as photo-catalyst, e.g. degradation of refractory organic substances... 

M. Gratzel, Colloidal semiconductors, in Photocatalysis, Fundamental and Applications, E. Pelizzetti, N. Serpone (eds.), J. Wiley and Sons, New York, 1989, pp. 123-157. 

M. A. El-Sayed, Small is different Shape-, size-, and composition-dependent properties of some colloidal semiconductor nanocrystals. Accounts Chem. Res. 37, 326—333 (2004). 

Gratzel, M. (1982) Artificial photosynthesis, light-driven electron transfer processes in organized molecular assemblies and colloidal semiconductors. Pure. Appl. Chem, 54, 2369-82. 

One of the most distinguishing features of semiconductor nanoparticles for use in photoelectrocatalysis is the absence of band bending at the semiconductor-electrolyte interface, see Fig. 4.2. In contrast to bulk behavior, for a colloidal semiconductor or a semiconductor comprised of a nanociystalline network in contact with an electrolyte the difference in potentials between the center (r = 0) of the particle and a distance r from the center can be expressed [83] ... 

Baral S, Eojhk A, Weller H, Henglein (1986) A Photochemistiy and radiahon chemistry of colloidal semiconductors 12 intermediates of the oxidahon of extremely small particles CdS, ZnS, CdsP2 and size quanhzahon effects (a pulse radiolysis study). J Am Chem Soc 108 375-378... 

Fischer CH, Weller H, Fojtik A, Lumepereira C, Janata E, Henglein A (1986) Photochemistry of Colloidal Semiconductors, 10. Exclusion Chromatography and Stop Flow Experiments on the Formation of Extremely Small Cds Particles. Ber Bimsen-ges 90 46-49... 

However, there are a number of difficulties associated with the synthesis of colloidal semiconductor particles. The preparation of stable, monodispersed, well-characterized populations of nanosized, colloidal semiconductor particles is experimentally demanding and intellectually challenging. Small and uniform particles are needed to diminish non-productive electron-hole recombinations the mean distance by which the charge carriers need to diffuse to reach the particle surface from which they are released is necessarily reduced in small particles. Monodispersity is a requirement for the observation of many of the spectroscopic and electro-optical manifestations of size quantization in semiconductor particles. Small semiconductor particles are difficult to maintain in solution in the absence of stabilizers flocculations and Ostwald ripening... 

Fig. 96. Schematic illustration of a colloidal semiconductor. Band-gap excitation promotes electrons from the valence band (VB) to the conduction band (CB). In the absence of electron donors and/or acceptors of appropriate potential at the semiconductor surface or close to it, most of the charge-separated, conduction-band electrons (e CB) and valence-band holes (h+VB) non-pro-ductively recombine. Notice the band bending at the semiconductor interface [500]...

Particles in the nanometer-size regime necessarily have large surface-to-volume ratios approximately one-third of the atoms are located on the surfaces of 40 A CdS particles, for example. Furthermore, colloid chemical preparations typically result in the development of surface imperfections and in the incorporation of adventitious or deliberately added dopants. Such surface defects act as electron and/or hole traps and, thus, substantially modify the optical and electro-optical properties of nanosized semiconductor particles. Altered photostabilities [595], fluorescence [579, 594, 596, 597], and non-linear optical properties [11, 598-600] are manifestations of the surface effects in colloidal semiconductors. 

Fig. 102. Schematics of available sites for organizing colloidal semiconductors in single-bilayer surfactant vesicles [500]...

Separate nanometer- to micron-sized colloidal semiconductors dispersed in solutions they are usually stabilized by polyions or polymers. 

Physically interconnected colloidal semiconductor particles supported by a monolayer, a BLM, or a solid substrate. 

Colloidal semiconductor particles were in situ generated and coated by catalysts in reversed micelles, surfactant vesicles and polymerized surfactant vesicles. 

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