Nonmetallic materials semiconductors

In modem technology an increasing number of nonmetallic materials, such as semiconductors, oxides, ionic crystals, and polymers, is employed, which corrode or degrade via chemical rather than electrochemical mechanisms. Corrosion protection of these materials by inhibitors is currently only marginally studied and will be an important future challenge for inhibitor science. For the important case of oxides, similar concepts as employed for the stabilization of passive films in the inhibition of localized corrosion should be applicable. 

In the following sections, we look at several nonmetallic materials with applications in modem technology. We begin with a discussion of the different allotropes or forms of carbon—diamond, graphite, and the fullerenes—where research has produced some exciting discoveries (Section 13.4). The fullerenes are recently discovraed molecular forms of the element carbon, in which the carbon atoms form hollow balls and tubes that may make them important as catalysts or possibly as drug-delivay mataials. Diamond shows promise as a material that might supersede silicon in its role as a matmal for sohd-state electronics. Silicon and diamond can act as semiconductors, which we discuss in Section 13.5. We end the chapter with sections on silicon, silica, and silicates (Section 13.6), ceramics (Section 13.7), and finally composites (Section 13.8). 

Here, the target of measurement by infrared ER spectrometry is a thin film deposited on a flat surface of a dielectric material. Multilayered adsorbed species (adsorbates) may also be a target, but, if a quantitative analysis of their observed spectra is to be performed, each layer in the adsorbate film should have a flat and parallel structure. For this reason, the discussion in this chapter assumes that thin films like a Langmuir-Blodgett (LB) film [4], which has an ideally flat layer, are the target of study. A dielectric substrate is made of a nonmetallic material and includes semiconductors the surface of water is also regarded as a dielectric substrate. Monolayers spread onto the surface of water are often analyzed by ER spectrometry. 

This classification is ratfier arbitrary, since different reaction products may form at the same electrode, depending on the reaction conditions. Nonmetallic substances such as oxides, semiconductors, and orgaihc N4 complexes are used as electrode materials as well. 

As early as 1943, Sommer (101) reported the existence of a stoichiometric compound CsAu, exhibiting nonmetallic properties. Later reports (53, 102, 103,123) confirmed its existence and described the crystal structure, as well as the electrical and optical properties of this compound. The lattice constant of its CsCl-type structure is reported (103) to be 4.263 0.001 A. Band structure calculations are consistent with observed experimental results that the material is a semiconductor with a band gap of 2.6 eV (102). The phase diagram of the Cs-Au system shows the existence of a discrete CsAu phase (32) of melting point 590°C and a very narrow range of homogeneity (42). 

It is possible to prepare thin foils from hard materials by mechanical methods alone. This is especially useful for modern nonmetallic electronic materials such as compound semiconductors and multication oxides. These materials are not easily polished chemically, and ion beams can cause unequal... 

Defects that introduce extra electrons, or that give missing electrons or holes , have a large influence on electronic conduction in nonmetallic solids. Most semiconductor devices use doped or extrinsic semiconductors rather than the intrinsic semiconduction of the pure material. Doping Si with P replaces some tetrahedrally bonded Si atoms in the diamond lattice (see Topic D2) with P. Each replacement provides one extra valence electron, which requires only a small... 

Production of any predetermined size of the particles can be generated through radiation chemical synthesis by controlling an easy-to-control parameter, radiation dose. Even a very small size can be obtained with monodispersity. Good crystallinity can be achieved and different phases of metal sulfide nanoparticles can be prepared just by choosing different nonmetallic sources and solvents (Qiao et al. 1999). A variety of nanocrystalline semiconductor materials has been synthesized so far in different media (Table 23.4). 

It should be mentioned at this point that not all aspects of the world of nanoparticles can be considered in a single volume. For instance, the rapidly developing field of nanorods and nanowires has again not been considered, as these species are indeed worthy of their own monographs. The terminus Nanoparticles, as in the First Edition, is restricted to metal and semiconductor species. Numerous other materials exist as nanopartides, while nonmetallic and oxidic nanopartides exist and exhibit interesting properties, especially with respect to their applications. Nevertheless, from a scientific point of view, metal and semiconductor nanopartides play perhaps the most interesting role, at least from the point of view of the Editor. 

Silicon is a nonmetallic chemical element that is used quite extensively in the manufacturing of transistors and various electronic and computer chips. Pure silicon is not found in nature it is found in the form of silicon dioxide in sands and rocks or found combined with other elements such as aluminum or calcium or sodium or magnesium in the form that is commonly referred to as silicates. Silicon, because of its atomic structure, is an excellent semiconductor, a material whose electrical conductivity properties can be chai d to act either as a conductor of electricity or as an insulator (preventor of electricity flow). Silicon is also used as an alloying element with other elements such as iron and copper to give steel and brass cert desired characteristics. 

In any metallic element or alloy, and thus 0 = — p is a materials constant. This is not true, however, in a nonhomogeneous or nonmetallic substance because the Fermi position is not a unique constant of the material. For example, in a semiconductor such as GaP, Ep can be made to vary 1-2 eV by doping , as described below. 

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