Nanocrystalline semiconductors

Trindade, T. O Brien, P. and Pickett, L. N. (2001). Nanocrystalline Semiconductors Synthesis, Properties and Perspectives. Chem. Mater., 13, 3843-3858. 

Kanatzidis MG, Pottgen R, Jeitschko W (2005) The metal flux a preparative tool for the exploration of intermetallic compounds. Angew Chem Int Ed 44 6996-7023 Trindade T, O Brien P, Pickett NL (2001) Nanocrystalline semiconductors Synthesis, properties, and perspectives. Chem Mater 13 3843-3858... 

Thin film coatings of nanocrystalline semiconductors, as collections of quantum dots (QD or Q-dot) attached to a solid surface, resemble in many ways semiconductor colloids dispersed in a liquid or solid phase and can be considered as a subsection of the latter category. The first 3D quantum size effect, on small Agl and CdS colloids, was observed and correctly explained, back in 1967 [109]. However, systematic studies in this field only began in the 1980s. 

The preceding treatment of the spin Hamiltonian terms in bulk semiconductors, where they are relatively-well understood, will provide a basis for the discussion of the NMR of nanocrystalline semiconductors in Sect. 4, since as a group they present special considerations and many unanswered questions remain. Section 5 will provide some general conclusions and suggest future promising avenues of NMR research in semiconductors. 

Nanocrystalline semiconductor thin film photoanodes, commonly comprised of a three dimensional network of inter-connected nanoparticles, are an active area of photoelectrochemistiy research [78-82] demonstrating novel optical and electrical properties compared with that of a bulk, thick or thin film semiconductor [79,80]. In a thin film semiconductor electrode a space charge layer (depletion layer) forms at the semiconductor-electrolyte interface charge carrier separation occurs as a result of the internal electric... 

Semiconductor nanoparticles have unique size-dependent photoelectrochemical properties. Demand for nanocrystalline semiconductors of uniform size and shape has stimulated research into different synthesis techniques some of which we consider here. 

A colloid chemical approach to CdS/HgS/CdS spherical quantum wells was described [79]. Size-dependent third-order non-linear susceptibilities of CdS clusters were investigated [80]. Reviews appeared on size-quantized nanocrystalline semiconductor films [81] and on the quantum size effects and electronic properties of semiconductor microcrystallites [82]. 

To date, one of the most promising applications has been the direct conversion of light into electricity with sensitized nanocrystalline semiconductor fdms. 

Figure 1 Schematic representation of a Gratzel solar cell. Sub-band-gap light absorption leads to the formation of the sensitizer excited state, followed by electron injection into the conduction band of the high-area nanocrystalline semiconductor. The electrons can be drawn into a circuit to do useful work and returned to the system through the redox mediator, the I/Ij" couple, at the counterelectrode.

Semiconductor photochemistry and photophysics play an important role in the broad field of supramolecular photochemistry. The unique properties of nanocrystalline semiconductor particles—which include quantum size effects on the band-gap, high surface area which is optimal for interfacial reactions, good photo- and thermal stability, and compatibility with the environment (i.e., green chemistry)—have led to an explosion of interest in the field. This volume of the Molecular and Supramolecular Photochemistry series provides chapters, authored by experts in the field, that discuss the area of semiconductor photochemistry and photophysics and highlight recent important advances in the area. 

R.W. Collins, P.M. Fauchet, I. Shimizu, J.-C. Vial, T. Shimada, and A.P. Alivisatos, Advances in Microcrystalline and Nanocrystalline Semiconductors—1996 (Materials Research Society, Pittsburgh, 1997). 

L.T. Canham, M.J. Sailor, K. Tanaka, and C.-C. Tsai, Microcrystalline and Nanocrystalline Semiconductors—1998 (Materials Research Society, Pittsburgh, 1999). 

In the past decade, lanthanide ions doped in nanocrystalline semiconductors have been the subject of numerous investigations. Although quantum size effects are not expected on lanthanide energy level structures, influence of quantum confinement in semiconductor on the luminescence properties of the lanthanides is expected. One of the advantages of lanthanide-doped semiconductor nanocrystals is that the lanthanide luminescence can be efficiently sen-... 

Lanthanides doped into nanocrystalline semiconductors have been the subject of numerous investigations in the past decades. If the size of a semiconductor particle is smaller than the Bohr radius of the excitons, the so-called quantum confinement occurs. As a result, the band gap of the semiconductor increases and discrete energy levels occur at the edges of the valence and conduction bands (Bol et al., 2002 Bras, 1986). These quantum size effects have stimulated extensive interest in both basic and applied research. 

The development of functional supramolecular devices remains mainly conceptual. However, photovoltaic devices are one of the few exceptions. Dye-sensitized nanocrystalline semiconductor materials have received significant interest as a result of their application in solar energy conversion. 

Figure 6.4 Correlation between space layer formation in bulk and nanocrystalline semiconductor particles...

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