Conductors, Semiconductors

Insulators can be distinguished from conductors or semiconductors in terms of their different conductivity at room temperature (T = 293 K) as shown in Table 3.3. 

To give a general description of covalent solids and metals, the band theory arising from the infinite polyene chain must be extended to three dimensions. The properties of solids depend largely on the way in which electrons fill the different available bands. 

The fact that a solid is a metal or a nonmetal will therefore depend on three factors (i) the separation of the orbital energies in the free atom (ii) the lattice spacing and (iii) the number of electrons provided by each atom. For a realistic description of the three-dimensional crystal, we must therefore extend our simple Hiickel theory5 in two respects. First, we must consider more than a single type of AOs (e.g. 2s, 2 p, 3d, ), and, second, we must consider more than an electron per atom. By increasing the 

5 In solid state theory called the tight-binding approximation (TBA) (see Table 3.4). 

HOMO/LUMO energy difference Hiickel theory 

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Semiconductors. The basic material employed in LEDs is the semiconductor, a soHd which possesses a conductivity intermediate between that of a conductor and an insulator. Unlike conductors, semiconductors and insulators possess an energy gap, E, between two energy bands, the... 

CVD in Electronic Applications Semiconductors 347 2.1 Conductors, Semiconductors, and Insulators... 

The description derived above gives useful insight into the general characteristics of the band structure in solids. In reality, band structure is far more complex than suggested by Fig. 6.16, as a result of the inclusion of three dimensions, and due to the presence of many types of orbitals that form bands. The detailed electronic structure determines the physical and chemical properties of the solids, in particular whether a solid is a conductor, semiconductor, or insulator (Fig. 6.17). 

By the nature of conduction and values of conductivity, materials can be classified as conductors, semiconductors, or insulators (dielectrics). It is a special attribute of conductors that free electric charges are present in them. The migration of these free charges in an applied electric field manifests itself as electric current. 

The conductors, semiconductors, and superconductors that have been discussed are materials that can be prepared via some type of CVD process. In order to prepare each material, a precursor is required. The precursor chemistry of these materials is based heavily on organometallic and inorganic chemistry. Numerous ligand platforms have been investigated for use in the preparation of suitable CVD precursors. 

The processible organic conductors, semiconductors, and insulators (not discussed in this chapter but well known historically for saturated polymers with sp3 electronic configuration) form fundamental material set for device applications. In the following sections, we discuss how to construct a PLED with such material set. 

The problem of preparation of pure ion-radical salts in solid state is very important technically. This problem is decisive in new application fields snch as organic conductors, semiconductors, and magnets. Especially, Chapter 8 of this book considers methods for the preparation of solid ion-radical salts for these materials. 

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... 

The very first information obtained is whether a given compound is a conductor, semiconductor or insulator. Such a basic answer is of importance concerning the 5 f localiza-... 

Materials can be classified as conductors, semiconductors or insulators. Conductors typically have resistivity in the range 10 2-103 xQ cm, semiconductors approximately 106-10n iQ cm, and insulators about 1013-1018 (xQ cm. Table 1.5 compares the electrical resistivity of the elements and compounds at room temperature. Although the carbides and nitrides have somewhat higher resistivity than do the pure metals, they still have resistivity in the regime of metallic conductors. In comparison the ceramic materials have much higher values, and are typically insulators. 

Symmetrical placement of the ion-selective membrane is typical for the conventional ISE. It helped us to define the operating principles of these sensors and most important, to highlight the importance of the interfaces. Although such electrodes are fundamentally sound and proven to be useful in practice, the future belongs to the miniaturized ion sensors. The reason for this is basic there is neither surface area nor size restriction implied in the Nernst or in the Nikolskij-Eisenman equations. Moreover, multivariate analysis (Chapter 10) enhances the information content in chemical sensing. It is predicated by the miniaturization of individual sensors. The miniaturization has led to the development of potentiometric sensors with solid internal contact. They include Coated Wire Electrodes (CWE), hybrid ion sensors, and ion-sensitive field-effect transistors. The internal contact can be a conductor, semiconductor, or even an insulator. The price to be paid for the convenience of these sensors is in the more restrictive design parameters. These must be followed in order to obtain sensors with performance comparable to the conventional symmetrical ion-selective electrodes. 

We continue with this hypothetical case of a conductor, whose work function changes on exposure to a certain chemical species, to discuss the second reason we listed for employing I-layers. In this example, we assume that there is no chemical reaction between the conductor and the semiconductor. Further, we assume here that this chemical species has only the effect of modifying the conductor work-function. For this demonstration of the second use of I-layers, it is assumed that there is a very high density of interface states at the conductor/semiconductor junction in the C-S configuration. Such a high density of states would pin the barrier height (the quantity... 

Semiconductors are materials with electrical conducting properties somewhere between those of insulators and conductors. Semiconductors are prepared from semimetals, most commonly silicon. Semiconductors are used in many electronic devices including computers. What makes these materials so popular is the ability to control the conductivity by the addition of small amounts of impurities called doping agents. 

There is a range of difficult technological and scientific hurdles that will need to be overcome before reliable products can be manufactured with the required performance at low cost by commercial printing techniques. A complete set of solution processible materials including not only conductors, semiconductors and di-... 

In the technology of ceramics, electronic conductors (semiconductors), ionic conductors (solid electrolytes) and mixed electronic-ionic conductors are encountered. In all cases the conductivity is likely to vary with temperature according to... 

Wilson ((>85) has pointed out that if a Brillouin zone is full, the electrons occupying the states of this zone can make no contribution to the electric current. This fact follows from the definition of the zone as a region enclosing all reduced wave vectors. Imagine all electrons of Figure 6 shifted Akx by an external field. The electrons in states within Akx of the zone boundary are reflected to the opposite zone boundary, so that the zone remains filled and there is no transfer of charge. This observation permits a sharp distinction between metallic conductors, semiconductors, and insulators. Because of the high density of states in a band, a crystal with partially filled bands is a metallic conductor. If all occupied zones (or bands) are filled, the crystal is a semiconductor if Ef kT, is an insulator if kT. 

The electric conductivity specifies the electric character of the material. Solid materials, in three groups of conductors, semiconductors, and insulators, exhibit a wide range of electric conductivities. Metals have conductivities on the order of 107 (fi m)-1, insulators have conductivities ranging between 10 10 and 10 20 (O m), and the conductivities of semiconductors range from 10 6 to 104 (O m). ... 

Carbon Fullerenes Chalcogenides Sohd-state Chemistry Defects in Solids Diffraction Methods in Inorganic Chemistry Ionic Conductors Semiconductors Superconductivity Zeolites. 

With respect to their conductivity, materials can roughly be divided into three categories metallic conductors, semiconductors and insulators. 

Some of the most important physical characteristics of selenium are its electrical properties. For example, selenium is a semiconductor. A semiconductor is a substance that conducts an electric current better than non-conductors, but not as well as conductors. Semiconductors have many very important applications today in the electronics industry. Selenium is often used in the manufacture of transistors for computers, cellular phones, and hand-held electronic games. 

An electric current is a flow of electrons. This movement of electrons can be used to carry information. Metals are good conductors of electricity non-metals are poor conductors. Semiconductors fall somewhere in between. Silicon s conductivity can be improved by the addition of phosphorus or boron—a process called doping. 

In Chapter 3, the Hiickel model of linear and closed polyene chains is used to explain the origin of band structure in the one-dimensional crystal, outlining the importance of the nature of the electronic bands in determining the different properties of insulators, conductors, semiconductors and superconductors. 

Another possible way of classifying soUds is according to their electrical properties as conductors, semiconductors or insulators. This aspect of the solid state is discussed briefly in Section 1.5. below. 

Figure 5.14 Resistance of conductors, semiconductors and superconductors as a function of temperature...

Next to the printing process, also materials for printed electronics have to be carefully engineered. Materials for printed electronics can be subdivided into conductors, semiconductors and dielectrics. However, it is important not to look at the single materials, but to combinations of materials with matching properties. An optimized transistor for instance has electrodes of a conductor plus a dielectric with properties that match those of the semiconductor, resulting in optimal device performance. Evonik aims to supply such system solutions for the printed electronics market. 

Keywords Liquid crystal Liquid-crystalline polymer Side-chain polymer Ion-conductor Semiconductor... 

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