Electrical techniques

A current-voltage technique was developed by Rajeshwar iS9 to study oil shales. When an electric field is applied to a solid substance, the current flowing through it is time-dependent. Two types of polarization mechanisms have been used to explain this time dependency linear polarization and nonlinear polarization. A convenient method of distinguishing between these is to examine the In versus In V plots (where is current density and V is the voltage). Linear polarization will result in curves with a slope of -I-1, whereas nonlinear polarization will give linear In Jx versus In J plots of slope 1. The oil shales reveal a complex behavior involving both linear and nonlinear polarization effects. 

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Experiments on transport, injection, electroluminescence, and fluorescence probe the spatial correlation within the film, therefore we expect that their response will be sensitive to the self-affinity of the film. This approach, which we proved useful in the analysis of AFM data of conjugated molecular thin films grown in high vacuum, has never been applied to optical and electrical techniques on these systems and might be an interesting route to explore. We have started to assess the influence of different spatial correlations in thin films on the optical and the electro-optical properties, as it will be described in the next section. 

A general disadvantage that limits the field of employing the electrical techniques of detecting EEPs is in the complexity of the hardware involved. As a rule, all electrical methods call for use of superhigh vacuum, the technique of excited particle bundles, the electron beam optics, and need high noise inununity. 

Zeenath, N. A. Pillai, P. K. V. Bindu, K. Lakshmy, M. Vijakakumar, K. P. 2000. Study of trap levels by electrical techniques in p-type CuInSe2 thin films prepared using chemical bath deposition. J. Mater. Sci. 35 2619-2624. 

The design requirements for intrinsically safe would seem to be demanding, and a review of NFPA 493 enforces this fact. Today s industrial environment imposes additional requirements not only on the use of intrinsically safe electrical circuits, but other hazardous electrical techniques as well. These requirements are due to the Occupational Safety and Health Act and the employer s increasing vulnerability for liability. 

In spite of the rigorous design requirements and the need for certification, instrinsically safe electrical circuits offer many advantages which the other hazardous location electrical techniques do not. 

Because of the very important role of impurities in determining semiconductor properties, it is desirable to know their concentrations, at least of the electrically active ones. Of course, the techniques we have discussed in this chapter never make a positive identification of a particular impurity without confirmation by one of the established analytical techniques, such as spark-source mass spectroscopy (SSMS) or secondary-ion mass spectroscopy (SIMS). Once such confirmation is established, however, then a particular technique can be considered as somewhat of a secondary standard for analysis of the impurity that has been confirmed. It must be remembered here that an analytical method such as SSMS will see the total amount of the impurity in question, no matter what the form in the lattice, whereas an electrical technique will see only that fraction that is electrically active. 

Moldavan A (1934). Photo-electric technique for the counting of microscopical cells. Science 80 188-189. 

New methods, more experimental and expensive, are emerging, which can improve the performance of electrical approaches, but for the forseeable future electrical techniques will remain the more basic and widespread methodology, and will remain useful provided their limitations are clearly understood and experimental conditions are designed to overcome the associated difficulties as much as possible. 

An electric technique to measure the gas holdup was implemented by Linek and Mayrhoferova (1969). In this method, the surface elevation of the gas-liquid interface of the nonaerated and aerated liquid in the vessel is detected at certain selected points by means of an electrical probe. The height is determined by the vertical position of the probe at which the sum of contact times equals one-half of the measurement period. The gas holdup is then calculated from the total surface elevation, the cross-section of the reactor, and the liquid volume. The accuracy of the measured value of the total surface elevation is claimed by the authors to be +0.2 mm. 

Flagan, R.C., Electrical techniques, in Aerosol Measurement, PA. Baron and K. Willeke, Eds., John Wiley Sons, New York, 2001. 

Insertion of transgenes into protoplasts can be achieved either by fusion of different protoplasts from different species, or DNA insertion into the protoplast through the plasmamembrane. Several approaches have been developed for this including a) chemical techniques, such as the use of PEG (polyethylene glycol), Ca -DNA co-precipitation or use of liposomes b) electrical techniques, where... 

Optical techniques like photoluminescence (10) and infrared photothermal spectroscopy (11.) work well for the characterization of shallow level impurities, while electrical techniques work well for deep level impurities. There are a number of methods that have been used for electrical characterization. I will only discuss deep level transient spectroscopy (DLTS), however, because it has become the most popular and gives a fairly complete characterization. 

Voltage contrast and Electron Beam Induced Current (EBIC), two electrical techniques usually used for circuit analysis, have proven useful for semiconductor materials characterization. 

Microscopic analysis, sieves or membrane techniques are also used for the separation of solids in waters [6], These optical, physical or electrical techniques are rather easy to use, but need specific and often expensive instruments. 

Individual cells can be identified on the basis of differences in size and dielectric properties using electrical techniques that are non-invasive and label-free. Characterization of the dielectric properties of biological cells is generally performed in two ways, with AC electrokinetics or impedance analysis. AC electrokinetic techniques are used to study of the behavior of particles (movement and/or rotation) and fluids subjected to an AC electric field. The electrical forces act on both the particles and the suspending fluid and have their origin in the charge and electric field distribution in the system. They are the basis of phenomena such as dielectrophoresis [10-14], travelling wave dielectrophoresis [15, 16], electrorotation [17, 18] and electroorientation [19]. 

In terms of cell lysis on-chip, Li and Harrison [39] were the first to report cell lysis through combination of a chemical method using SDS and electrical techniques. Since then, other on-chip lysis methods have appeared, including mechanical [40], thermal [41], ultrasonic [42], and electrophoretic [43, 44]. 

Since a number of different techniques are included under the broad term of thermoelectrometry, this discussion will be divided into three categories (1) electrical conductance, current, and resistance (2) dielectric constant and capacitance and (3) miscellaneous electrical techniques that are of interest to thermal analysis. 

Electrical techniques primarily measure the electrical impedance of a mixed-phase medium. Because the dielectric constant or electrical conductivity of a solid phase differs from that of the fluid, one can measure electrical conductance or capacitance to determine phase distribution. To attain better sensitivity, conductance flowmeters are usually applied to conducting media, such as aqueous solutions or solids/water slurries, whereas capacitive flowmeters are applied to solid/gas flows and solid/nonconducting-liquid flows. Capacitance measurements are generally more reproducible because they are not affected by the ion concentration of the solution, which is difficult to control during processing. 

Electrical studies The electrical analysis on gum Arabica includes a wide range of studies that extract the electroactive nature of gum specimens. Almost each and every electrical technique is based on electrical conductivity measurement. The electrical conductivity of an electrolyte is given in Equation 12.3,... 

In electrochemistry, because electrical quantities are easy to use and provide information directly relating to the behavior of the interface, they are particularly useful to identify interfacial processes. Contrary to other techniques, which require a vacuum chamber [low-energy electron diffraction (LEED), Auger electron spectroscopy, etc.] or electromagnetic radiation (optical ellipsometry, or X-rays EXAFS), which need no alteration of the electrode surface, electrical techniques can be used in situ on any surface state of the electrode. In addition, thanks to the advances in electronics, experimentalists can use more and more sophisticated... 

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