Semiconducting particles, particle sizes

As mentioned above, the electronic properties of SWCNTs depend on their chirality and may be semiconducting or metallic. There is still no satisfying way to produce just one sort of SWCNTs, which would require the exact control of catalyst particle size at elevated temperature. Hence, the separation of semiconducting from metallic SWCNTs is of paramount importance for their application in, for example, electric devices, field emission and photovoltaics etc. 

The membrane-mimetic approach has the potential of providing superior size, morphology, and monodispersity control for ceramic particles. The relatively meager amount of published work in this area [826-834] (see Table 11) is rather surprising. Vigorous and sustained activities, inspired by biomineralization [15-18] and modeled on the incorporation of metallic, catalytic, and semiconducting particles into membrane-mimetic compartments, are fully expected. 

When the particle sizes of semiconducting materials become smaller than about 100 A. their band gap energies become larger. The band structure aillapses, and discrete energy levels appear. Therefore, such small (and size quantized) semiconducting particles show a remarkable blue shift and clear structure in their absorption spectra. 

The main approach to reach higher sensor sensitivity is based on maximization of the electron depletion layer compared with the semiconducting core this can be realized by decreasing the particle size down to the scale of the depletion layer thickness.6-8 Oxide semiconductors in the form of nanocrystalline powders,9-11 nanorods,12 nanowires,13-15 nanotubes,1617 and nanobelts18 with a high surface area/ volume ratio have been studied intensively as highly sensitive materials. 

Finally, a study of fairly monodisperse CdSe semiconducting nanorods functionalized with amphiphilic molecules in a suspension of cyclohexane has recently been published that shows preliminary results indicative of a typical nematic behavior [ 102]. Note that these nanorods have been synthesized by the pyrolysis of organometallic precursors of Cd and Se in hot surfactant mixture allowing a good control of the aspect ratio. This state of the art particle size and shape control method should allow one to customize accurately their semiconducting properties. 

The rate of photocorrosion depends on the size of the semiconducting sulfide particles. 

A semiconductor can be doped with donor atoms to provide electrons to the conduction band. Semiconducting materials can also be doped with acceptor atoms that take electrons from their valence band and leave behind some positive charges (holes). The most effective properties of semiconducting nanoparticles are noticeable changes in their optical properties which differ from their bulk counterpart materials. There is a significant shift in the optical absorption spectra toward the blue region (shorter wavelengths) as the particle size is reduced [360]. 

The microstructure of the semiconducting particles and the surface composition, both of which are characterized by the crystallite size D, the grain-size distribution, and the coagulation structure, all subject to some control through the inclusion of additives,... 

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