Alternating current properties

This chapter is dedicated to the basics of the silicon-electrolyte contact, with emphasis on the semiconductor side of the junction. The phenomenology of the I-V curve is discussed, together with basic charge states of semiconductor electrode like accumulation, depletion and inversion. Electrostatic and electrodynamic properties will be described, with emphasis on the direct current (DC) properties of the semiconductor electrode, while alternating current (AC) properties are discussed in Section 10.2. Details of charge exchange and mass transport as well as details of the reactions at the microscopic level are considered in Chapter 4. 

Cation—sulfonate interactions, as well as proton mobility, are also expressed in the electrical conductance behavior of these membranes. Many studies of this property have been reported, and there is no attempt in this review to cite and describe them all. Rather, a few notable examples are chosen. Most testing is done using alternating current of low voltage to avoid complications in the form of chemical... 

Some important dielectric behavior properties are dielectric loss, loss factor, dielectric constant, direct current (DC) conductivity, alternating current (AC) conductivity, and electric breakdown strength. The term dielectric behavior usually refers to the variation of these properties as a function of frequency, composition, voltage, pressure, and temperature. 

Selenium has many industrial uses, particularly electronic and solid-state applications, which have increased phenomenally in recent years. This is attributed to its unique properties (1) it converts light directly to electricity (photovoltaic action) (2) its electrical resistance decreases with increased illumination (photoconductivity) and (3) it is able to convert alternating current to direct current. 

Impedance spectroscopy is a versatile electrochemical tool, helpful to characterize the intrinsic dielectric properties of various materials. The basis of this technique is the measurement of the impedance (opposition to alternating current) of a system, in response to an exciting signal over a range of frequencies (Bard and Faulkner, 2001). 

Impedance spectroscopy may provide quantitative information about the conductance, the dielectric coefficient, the static properties of a system at the interfaces, and its dynamic changes due to adsorption or charge-transfer phenomena. Since in this technique an alternating current with low amplitude is employed, a noninvasive observation of samples with no or low influence on the electrochemical state is possible. 

Nevertheless, the mid-peak potentials determined by cyclic voltammetry and other characteristic potentials obtained by different electroanalytical techniques (such as pulse, alternating current, or square wave voltammetries) supply valuable information on the behavior of the redox systems. In fact, for the majority of redox reactions, especially for the novel systems, we have only these values. (The cyclic voltammetry almost entirely replaced the polarography which has been used for six decades from 1920. However, the abundant data, especially the half-wave potentials, 1/2, are still very useful sources for providing information on the redox properties of different systems.)... 

In 1909, Dr. E. Weintraub of the General Electric Company ran high-potential alternating current arcs between cooled copper electrodes in a mixture of boron chloride with a large excess of hydrogen (51), obtaining pure fused boron which differed greatly in properties from the impure amorphous product of earlier workers. 

The remarkable electrical property of germanium that caused the unprecedented demand for it is its ability to permit the flow of electricity in one direction and resist the flow in the other direction. Although vacuum tubes are used m tire construction of rectifiers to convert alternating current to direct current, many of them are bulky, fragile, and not sufficiently durable. A germanium rectifier only a few millimeters in diameter dissipates no heat, reacts instantly, and has about ten times the average life of a vacuum tube. 

The most exciting property of these materials is that thin polycrystalline films can behave as two dimensional Josephson Tunnel Junction Arrays (110) displaying remarkably good electromagnetic coupling (111) both as emitters and receivers. Alternating current to direct current conversion has been observed in bulk samples (112), but the thin film geometry allows use of one film as a radiation emitter, and another film as the receiver (111). 

The most important dielectric properties are the dielectric constant, e, and the dielectric loss factor, tan 8. These properties are of interest for alternating currents indicates the polarizability in an electric field, and, therefore, it governs the magnitude of the alternating current transmitted through the material when used in a capacitor. For most polymers e is between 2 and 5, but it may reach values up to 10 for filled systems. 

The electrical properties of polyelectrolyte complexes are more closely related to those of biologically produced solids. The extremely high relative dielectric constants at low frequencies and the dispersion properties of salt-containing polyelectrolyte complexes have not been reported for other synthetic polymers. Neutral polyelectrolyte complexes immersed in dilute salt solution undergo marked changes in alternating current capacitance and resistance upon small variations in the electrolyte concentration. In addition, their frequency-dependence is governed by the nature of the microions. As shown in... 

When it is struck or pressed, quartz generates an electric current. Materials having this property are known as piezoelectric materials. If an external voltage is applied across the crystal, the crystal undergoes vibrations that are in resonance with the alternating current frequency. This type of behavior is the basis for quartz being used as a timing device in watches or in crystals used to establish radio frequencies. 

The dielectric properties were measured by using an alternating current impedance analysis apparatus (HP-4294A). 

J. F. McClendon, R. Rufe, J. Barton, and F. Fetter, "Colloidal Properties of the Surface of the Living Cell 2. Electric Conductivity and Capacity of Blood to Alternating Currents of Long Duration and Varying in Frequency from 260 to 2,000,000 Cycles per Second," Journal of Biological Chemistry, 69 (1926) 733-754. 

Of what valne is it to have a semicondnctor that can condnct an electric cnrrent by the flow of electrons if it is n-type or by the flow of holes if it is p-type Many electronic functions can be fnlfilled by semiconductors that possess these properties, but the simplest is rectification—the conversion of alternating current into... 

In the majority of numerical calculations of the anomalous frequency behavior of such composites (in particular, near the percolation threshold pc) under the action of an alternating current, lattice (discrete) models have been used, which were studied in terms of the transfer-matrix method [91,92] combined with the Frank-Lobb algorithm [93], Numerical calculations and the theoretical analysis of the properties of composites performed in Refs. 91-109 have allowed significant progress in the understanding of this phenomenon however, the dielectric properties of composites with fractal structures virtually have not been considered in the literature. 

The fractal concept has proved to the helpful in describing such systems. In this connection our attention has been focused on using the fractal concept to make predictions concerning the physical properties of inhomogeneous media with a random structure. We remark that numerous other examples of fractal behavior than those treated here appear in the literature. We should mention resistance capacitance transmission lines [240] and fractal models for the alternating current response at a rough interface between materials of very dissimilar conductivities [241,242] and how a resistance capacitance line may be used as a semiintegrator [243]. 

Polar molecules display the property that they can be oriented along an electric field dipolar polarization phenomenon). In the absence of this phenomenon, dipoles are orientated at random and molecules submitted to Brownian movement only. In the presence of a continuous electric current, aU the dipoles are lined up together in the same direction. If submitted to an alternating current, the electric field is inversed at each alternance with a subsequent tendancy for dipoles to move together to follow the field. Such a characteristic induces stirring and friction of molecules which dissipates as internal homogeneous heating (Scheme 21). 

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