Electrical properties phenomena

The principal use of gold is as a very thin coating about 0-05 /xm thick for electrical and electronic applications. Because of the thinness of gold electrodeposits, porosity must be very carefully controlled since seepage of corrosion products from substrate or undercoat exposed at these pores can have serious adverse effects on both appearance and electrical properties of the composite. The porosity can vary with the thickness of the deposit (Fig. 13.1), and with the type of plating bath and with its method of operation (Fig. 13.2), and the phenomenon has been extensively studied by Clarke and many other workers. 

Microbial deterioration of plastics is intimately involved with the moisture problem, especially with regard to plastics in electronic equipment. For this reason much of the literature treats the two problems together. Furthermore, there is often confusion between the deterioration of the electrical properties of plastics, more often than not a moisture phenomenon, and actual deterioration of the substance of the polymer. 

To dissociate molecules in an adsorbed layer of oxide, a spillover (photospillover) phenomenon can be used with prior activation of the surface of zinc oxide by particles (clusters) of Pt, Pd, Ni, etc. In the course of adsorption of molecular gases (especially H2, O2) or more complex molecules these particles emit (generate) active particles on the surface of substrate [12], which are capable, as we have already noted, to affect considerably the impurity conductivity even at minor concentrations. Thus, the semiconductor oxide activated by cluster particles of transition metals plays a double role of both activator and analyzer (sensor). The latter conclusion is proved by a large number of papers discussed in detail in review [13]. The papers cited maintain that the particles formed during the process of activation are fairly active as to their influence on the electrical properties of sensors made of semiconductor oxides in the form of thin sintered films. 

TCNQ-Polyphosphazene Systems. Tetracyanoquinodimethane (XX) salts crystallize in the form of stacked arrays that allow electrical semiconductivity (42). Although this phenomenon has been studied in many laboratories, it has not been possible to fabricate conductive films or wires from these substances because of the brittleness that is characteristic of organic single crystals. However, it seemed possible that, if the flexibility and ease of fabrication of many polyphosphazenes could be combined with the electrical properties of TCNQ, conducting polymers might be accessible. 

The phenomenon of superconductivity was discovered at the beginning of the twentieth century by the Dutch physicist H. Kamerlingh Onnes, during the first attempts to liquefy helium (which at atmospheric pressure boils at 4.2 K). After refining the technique of helium liquefaction, in 1911, Onnes attempted to measure the electrical resistance of metals at these extraordinary low temperatures, and realized that at 4 K the resistance of mercury, as well as that of other metals indicated in Figure 1, became too low to be measured. This change in electrical property became the indication of the new superconductive physical state. The temperature below which materials become superconducting is defined as the critical temperature, Tc. 

The reaction of solid porphyrin films with light in the presence of oxygen by producing MgTPP must affect electrical properties, in particular semi conduct on, photoconduction, and photovoltaic properties. We have provided evidence for "photodoping" by light and oxygen, a phenomenon that must be clearly understood if these materials are to have device applications. 

Thus, protein adsorption and cell adhesion occur for various reasons and in different appearances. When surfaces of living systems are involved, specific recognition mechanisms undoubtedly play crucial roles. Nevertheless, since we are dealing with a rather general phenomenon, it is likely that these specific interactions are superimposed on a generic interaction mechanism. Bioadhesion and adsorption is very complicated from a physical chemical point of view. Interfacial tensions, wetting and electrical properties of the surfaces are prominently involved. 

The BNC nanotubes can have a metallic behavior if they do not have a band gap or a semi conductor behavior if there are band gaps. The importance of this phenomenon is that the electric properties of BCN compoimds can be controlled by varying the atomic composition and atomic arrangement of the compounds. In addition, their mechanical properties could be similar to these of diamond and cubic BN, providing new super-hard materials [14]. 

We analyze theoretically the phenomenon of photon-assisted quantum transport in superconductor(S)- semiconductorfN) mesoscopic system. Sub-gap structures in the I-V characteristics could be explained by multiple Andreev reflections. The electrical properties are strongly determined by the interface between superconductor and semiconductor. The current - voltage characteristics were found to be very sensitive to the photon frequency. 

The mechanical and electrical displacements for metalized and free surfaces at liquid-36 YX LiTa03 interface are shown in Figure 4.4a and 4.4b [22]. Most of the acoustic energy is conhned to within one wavelength from the surface of the substrate. When the surface is metalized and electrically shorted, the potential on the surface is zero. In this case, only the normalized displacement (U2) interacts with the liquid loading, and the phenomenon is called mechanical perturbation. If the surface is free and electrically open, then both U2 and normalized electric potential (d>) interact with the adjacent liquid medium (Figure 4.4b). Interactions of d> and the electrical properties of the liquid constitute the acoustoelectric interaction. The influence of both the mechanical and acoustoelectrical interactions on sensor response and material characterization is discussed in the subsequent sections. 

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