Nanocomposite semiconductor

Nanocomposite semiconductors such as nanowires arrays of CdZnTe can be used for detecting low-energy gamma rays (Gandhi et al. 2008). The CdZnTe compound semiconductor is electrodeposited in the form of nanowires onto a Ti02 nanotubular template. The preKminary results indicate that the CZT nanowire arrays can be used as radiation detector materials at room temperature with a much lower bias potential (0.7-2.3 V) as compared to the 300-500 V applied to bulk detector materials. 

Ramrakhiani [155] has reported the EL in nanocrystals and nanocomposites. Semiconductor nanocrystals exhibit many unique properties, which are promising for the improvement of electroluminescence (EL) devices. Combination of polymer and semiconductor nanocrystals allows the fabrication of flexible and lightweight EL devices. The incorporation of nanocrystals in polymer is expected to increase the life of the device and enhance the brightness of emission. The II-VI semiconductor nanoparticles and the nanocomposites in polymers have been synthesized by chemical route. The samples have been characterized and their electroluminescence has been investigated. 

The synthesis of MNCGs can be obtained by sol-gel, sputtering, chemical vapor-deposition techniques. Ion implantation of metal or semiconductor ions into glass has been explored since the last decade as a useful technique to produce nanocomposite materials in which nanometer sized metal or semiconductor particles are embedded in dielectric matrices [1,2,4,23-29]. Furthermore, ion implantation has been used as the first step of combined methodologies that involve other treatments such as thermal annealing in controlled atmosphere, laser, or ion irradiation [30-32]. 

The formation of nanocomposites can be done using different arrangements, for example, the dispersion of a semiconductor in a continuous matrix, the formation of stacked layers, core-shell geometries, or simply physically contacted, with consequences for the energy transfer between the phases (Figure 4.5) [76]. 

Figure 4.5 Schematic representation of four different possibilities to form semiconductor nanocomposites from a semiconductor A (SCA) and a semiconductor B (SCB), namely...

Although the terms nanocomposite and hybrid are often used to define similar materials, we will use the classification indicated by Vilatelaand Eder [1], Nanocomposites are multiphase materials, in which one phase is dispersed in a second phase, resulting in a combination of the individual properties of the component materials. The volume fraction of the nanocarbon is typically less than a few percent. Nanocarbon hybrids are instead formed by both components with similar volume fractions. The inorganic compound (such as semiconductor nanoparticles) is deposited onto the surface of the... 

Nonlinear optics, lithography, conductors, semiconductors, piezoelectronic, pyroelectronic, solar energy conversion, electrodes, computer chip circuitry UV absorption, smart materials, nanocomposites, laser, sealants, paints, caulks, lubricants, gaskets... 

Materials development and synthesis is another important dual-use type of chemistry. Developments over the past few decades include a number of elec-troitic materials and their processing, fuel cells and batteries, photoresist and semiconductor synthesis, high-performance composites (structural components) and nanocomposite materials, colloidal nanoparticle technology, solid-state lasers, and light-emitting diodes. 

While the variety of NPs used in catalytic and sensor applications is extensive, this chapter will primarily focus on metallic and semiconductor NPs. The term functional nanoparticle will refer to a nanoparticle that interacts with a complementary molecule and facilitate an electrochemical process, integrating supramolecular and redox function. The chapter will first concentrate on the role of exo-active surfaces and core-based materials within sensor applications. Exo-active surfaces will be evaluated based upon their types of molecular receptors, ability to incorporate multiple chemical functionalities, selectivity toward distinct analytes, versatility as nanoscale receptors, and ability to modify electrodes via nanocomposite assemblies. Core-based materials will focus on electrochemical labeling and tagging methods for biosensor applications, as well as biological processes that generate an electrochemical response at their core. Finally, this chapter will shift its focus toward the catalytic nature of NPs, discussing electrochemical reactions and enhancement in electron transfer. 

The formula (11) in view of relations for /ie and /ih describes above-mentioned basic features of size effects in semiconductor crystal. It is important that as against metals, semiconductors show appreciable quantum dimensional effects at the sizes of particles from 3 to lOnm (depending on electronic structure of the semiconductor and sizes of AE0) [20]. Such nanoparticles are usually formed at synthesis of nanocomposite films. 

Similar histograms were determined by TEM for Pb-, Zn-, and Cd-containing nanocomposite PPX films prepared by vapor deposition cryochemical synthesis [85]. The value d of metal nanocrystals in these films is also 5nm. The same approximately size d ( 4.5nm) has been evaluated from Ai/2 of X-ray diffraction peak for semiconductor PbS nanocrystals in PbS-PPX nanocomposite [71]. It should be particularly emphasized that d value of M/SC nanocrystals embedded by cryosynthesis in PPX and C1PPX matrices does not depend on M/SC content as for low loading (0.2-2 vol.% for Ag in PPX and C1PPX [75, 80] and 0.01-1 vol.% for Pb in PPX [85]) and for high loading (5-11 vol.% for PbS in PPX [3, 71, 86]) systems. 

Some applications are at a fundamental research stage with associated higher risk, i.e. electroless coating, semiconductors, anodising, nanocomposite coatings. 

Keywords photocatalysis, hydrogen evolution, Ti02, semiconductor nanoparticles, sol-gel synthesis, template synthesis, mesoporous materials, metal-semiconductor nanocomposites... 

Dawson A., Kamat P.V. (2001) Semiconductor-metal Nanocomposites. Photoinduced Fusion and Photocatalysis of Gold-Capped Ti02 (Ti02/Gold) Nanoparticles, J. Phys. Chem. B. 105(5), 960-966. 

Keywords. Dendrimer, Metal nanoparticles, Semiconductor nanoparticles, Nanocomposites... 

Cozzoli, P.D., R. Comparelli, E. Fanizza, M.L. Curri, A. Agostiano and D. Laub (2004a). Photocatalytic synthesis of silver nanoparticles stabilized by Ti02 nanorods A semiconductor/metal nanocomposite in homogeneous nonpolar solution. Journal of the American Chemical Society, 126(12), 3868-3879. 

Kawahara, K., K. Suzuki, Y. Ohka and T. Tatsuma (2005). Electron transport in silver-semiconductor nanocomposite films exhibiting multicolor photochromism. Physical Chemistry Chemical Physics, 7(22), 3851-3855. 

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