Semiconductor cores

Cao YW, Banin U (2000) Growth and properties of semiconductor core/shell nanocrystals with InAs cores. J Am Chem Soc 122 9692-9702... 

Some important observations, which should apply de facto to many nematic systems containing dispersed nanoparticles, particularly those with metal or semiconductor cores, were reported in 2006 by Prasad et al. [297]. The authors found that gold nanoparticles stabilized with dodecanethiol decreased the isotropic to nematic phase transition of 4-pentyl-4 -cyanobiphenyl (5CB) almost linearly with increasing nanoparticle concentration (x p) and increased the overall conductivity of these mixtures by about two orders of magnitude. However, the anisotropy of the electric conductivity (Act = [Pg.349]

On the other hand, when low concentrations of metal are used to cap the semiconductor core we can expect the outer layer to be discontinuous. Such a configuration of core shell particles (i.e. small metal islands deposited on the Ti02 core) provides a favorable geometry for facilitating the interfacial charge transfer under UV irradiation. It should be noted that, a new band appears at 390 nm in the case of Ti02/Au nanoparticles as the transient absorption corresponding to (SCN)2 ... 

Figure 35 The total-energy variation when interchanging a close S Se pair between the core and the shell of semiconductor core/shell nanoparticles. The reaction coordinate equals 0 before and 1 after the interchange, and the AaBbCcDd notation means an AaBb core covered by a CcDd shell before the interchange...

Bardhan, R., Grady, N.K., Ali, T., and Halas, N.J. (2010) Metallic nanoshells with semiconductor cores optical characteristics modified by core medium properties. ACS Nano, 4, 6169-6179. 

Thus, semiconductor core-shell nanocrystals can exhibit a huge enhancement of optical transitions lying in the spectral range from 10 microns to submillimeters. 

Coating a given ensemble of nanoparticles with another material yields core-shell nanocrystals (see above see also Refs [272,273]). In these structures, the cores may be any type of colloidal particle, such as metals, insulators, and all classes of semiconductors. Likewise, the shells may consist of type of material, including organics. At this point, attention is focused on semiconductor cores and inorganic shells, mainly of semiconductor materials. 

This section first provides a general discussion of the synthetic strategy employed for group III-V semiconductor nanocrystals, followed by a description of the synthesis of InAs nanocrystals as a prototypical example. The characterization of the particles produced, using a variety of methods, is briefly reviewed, after which details are provided of the synthesis of core-shell nanocrystals with III-V semiconductor cores, focusing particularly on InAs cores. 

In semiconductors, core levels are shifted because of charge transfer between surface atoms. Table 5.2-15... 

Gu CK, Xu H, Park M, Shamion C (2009) Synthesis of metal-semiconductor core-shell nanoparticles using electrochemical surface-limited reactions. Langmuir 25(1) 410- 14... 

The hot-soup method has also been applied to the production of semiconductor core/shell nanostructures, where a semiconductor nanocrystal is coated with a second semiconductor of wider bandgap. Shown in Figure 23 is a scheme for the synthesis of CdSe/CdS core/shell nanocrystals. These nanostructures were synthesized via a high-temperature route in a mixture of TOP and TOPO (223,224) and via a low-temperature route in pyridine (225). Among the semiconductor core/shell nanomaterials produced were CdSe/ZnS, CdSe/CdS, InAs/InP, InAs/CdSe, InAs/ZnSe, and InAs/ZnS (223,225-228). In these structures, the shell type and thickness allow further control of the optical, electronic, and other properties of semiconductor nanocrystals. For example, the shell may be used to passivate the imperfect surface of the core semiconductor, resulting in significantly improved luminescence efficiency. 

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