Semiconductor-based composites

Rajeshwar, K., de Tacconi, N.R., and Chenthamarakshan, C.R. (2001) Semiconductor-based composite materials preparation, properties, and performance. Chemistry of Materials,... 

Fig. 1 Four types of semiconductor-based composite architectures (a) semiconductor/matrix (b) layered configuration of two semiconductors, A and B (c) coupled semiconductors (d) core-shell geometry SC denotes the semiconductor [12]...

Krishnan R., Nouia R. de Tacconi, Chenthamarakshan C. R. (2001) Semiconductor-Based Composite Materials Preparation, Propaties, and Perfouiance. Chem. Mater. 13 2765-2782... 

Composite semiconductors Semiconductor mixing (composite) is another strategy for developing photocatalysts with visible-light response from photocatalysts with a wide band gap. This strategy is based on the coupling of a wide band-gap semiconductor with a narrow band semiconductor with... 

As a probe of lattice vibrations, Raman spectroscopy is very sensitive to intrinsic crystal properties and extrinsic stimuli, especially in semiconductors. It may be employed to study crystal structure and quality, crystal orientation, optical interactions, chemical composition, phases, dopant concentration, surface and interface chemistry, and local temperatme or strain. As an optical technique, important sample information may be obtained rapidly and nondestructively with minimal sample preparation. Submicron lateral resolution is possible with the use of confo-cal lenses. These features have made it a vital tool for research labs studying semiconductor-based technologies. They also are increasingly important for the study of semiconductor NWs fabricated by both top-down and bottom-up approaches since many of the common characterization methods used with bulk crystals or thin films cannot be applied to NWs in a direct manner. 

Nanocomposites in the form of superlattice structures have been fabricated with metallic, " semiconductor,and ceramic materials " " for semiconductor-based devices. " The material is abruptly modulated with respect to composition and/or structure. Semiconductor superlattice devices are usually multiple quantum structures, in which nanometer-scale layers of a lower band gap material such as GaAs are sandwiched between layers of a larger band gap material such as GaAlAs. " Quantum effects such as enhanced carrier mobility (two-dimensional electron gas) and bound states in the optical absorption spectrum, and nonlinear optical effects, such as intensity-dependent refractive indices, have been observed in nanomodulated semiconductor multiple quantum wells. " Examples of devices based on these structures include fast optical switches, high electron mobility transistors, and quantum well lasers. " Room-temperature electrochemical... 

Dielectric materials will not conduct electricity and as such are of critical importance as capacitive elements in electronic applications and as insulators. It could be argued, with some justification, that without the discovery of new compositions with very high charge-storing capabilities, i.e., relative dielectric constants k > 1000, the impressive miniaturization of semiconductor-based devices and circuits would not have been as readily implemented. In addition, the traditional use of ceramics as insulators in high-power applications is still a substantial economic activity. 

Chapters 12 and 13 cover two of the most important novel catalytic applications of carbon materials, electrocatalysis and photocatalysis. In the first case, carbons are used mostly as supports for metal catalysts in fuel cells, while the synergistic effects of carbon-based composite semiconductor materials, such as C-TiOi, make them particularly effective in photocatalytic degradation reactions. 

In materials science we often divide materials into distinct classes. The primary classes of solid materials are ceramics, metals, and polymers. This classification is based on the types of atoms involved and the bonding between them. The other widely recognized classes are semiconductors and composites. Composites are combinations of more than one material and often involve ceramics, such as fiberglass. Semiconductors are materials with electrical conductivities that are very sensitive to minute amounts of impurities. As we will see later, most materials that are semiconductors are actually ceramics, for example, gallium nitride, the blue-green laser diode material. 

If you look in any introductory materials science book you will find that one of the first sections describes the classification scheme. In classical materials science, materials are grouped into five categories metals, polymers, ceramics, semiconductors, and composites. The first three are based primarily on the nature of the interatomic bonding, the fourth on the materials conductivity, and the last on the materials structure—not a very consistent start. 

Besides clay-based nanocomposites, there has been huge discussion on the metallic and semiconductor-based hybrid materials. The ability of polymer materials to assemble into nanostructures describes the use of polymers providing exquisite order to nanoparticles. Finally, a discussion on potential applications of polymer—nanoparticle composites with a special focus on the use of dendrite polymers and nanoparticles for catalysis should follow (Polymer-Nanoparticle Composites Part 1 (Nanotechnology), 2010) (Figure 1.15). 

Epoxy/cyanate ester thermoset blend-based composites have low dielectric constant desirable for advanced radomes, microwave anteimas, and stealth aircraft composite applications. Other applications include its use in copper clad laminates, semiconductor devices, and fire-resistant aircraft structural composites. 

Some measurements of this property have been made in a range of electrically conducting polymers. These include epoxy resin/polyaniline-dodecylbenzene sulfonic acid blends [38], polystyrene-black polyphenylene oxide copolymers [38], semiconductor-based polypyrroles [33], titanocene polyesters [40], boron-containing polyvinyl alcohol [41], copper-filled epoxy resin [42], polyethylidene dioxy thiophene-polystyrene sulfonate, polyvinyl chloride, polyethylene oxide [43], polycarbonate/acrylonitrile-butadiene-styrene composites [44], polyethylene oxide complexes with sodium lanthanum tetra-fluoride [45], chlorine-substituted polyaniline [46], polyvinyl pyrolidine-polyvinyl alcohol coupled with potassium bromate tetrafluoromethane sulfonamide [47], doped polystyrene block polyethylene [38, 39], polypyrrole [48], polyaniline-polyamide composites [49], and polydimethyl siloxane-polypyrrole composites [50]. 

Beside their well-known extra-high mechanical properties, single-walled carbon nanotubes (SWNTs) offer either metallic or semiconductor characteristics based on the chiral structure of fullerene. They possess superior thermal and electrical properties so SWNTs are regarded as the most promising reinforcement material for the next generation of high performance structural and multifunctional composites, and evoke great interest in polymer based composites research. The SWNTs/polymer composites are theoretically predicted to have both exceptional mechanical and functional properties, which carbon fibers cannot offer [105]. 

Moffit, M. et al. (1995) Size control of nanoparticles in semiconductor-polymer composites. 2. Control via sizes of spherical ionic microdomains in styrene-based diblock ionomers. Chemistry of Materials, 1,1185-1192. 

Another important category of conducting polymer-based composites includes films containing metal, metal oxide, clay, carbon black, semiconductor, and other types of particles (Table 20.17). These composites can be synthesized electrochemically by polymerizing the parent monomer (pyrrole, thiophene, or aniline) in a dis-... 

The performance of both types of composites in OPVs is still modest as compared to semiconductor-based solar cells. Improvement in the layer morphology and development of low-bandgap organic materials can lead to higher power conversion efficiencies. An estimation of the maximum expectable efficiency of bulk hetero-junction cells predicts that 10% for solar cells will be reached in the next few years, while practical values of 20-25% would be the limits of the best devices, still to be realized [92]. However, even with low but acceptable rj 5%, mass production of low-cost cells will be a nice solution for renewable energy sources. The main and difficult to solve issue is the stability of the devices, which should attain industrial commercialization requirements. Stable operation for more than 4000 h has been reported for P3HT PCBM bilayer structure cells and can be further improved [93]. 

This section includes a discussion of formulated products which contain wax. A fluori-nated copolymer was used in a wax composition for car body refinishing. A mixture of ethyl acetate, toluene and heptane is used as a solvent. A cleaning and polishing composition for automobiles is also based on a fluorinated polymer and eontains hydrocarbon solvent at up to 70%." Universal auto lotion is a water/solvent emulsion of wax." It contains isoparaffinic solvents. A car polish formulation contains 10-35% mineral spirits." A semiconductor polishing composition contains alcohols, acid and water. "... 

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