Transient current methods

The TSC signal strength will be proportional to the appropriate trap density, as seen in Eq. (55). Unfortunately, the lifetime t (or xp for hole emission) also enters the equation, and this quantity will depend on other traps and recombination centers in the sample. If t could be separately determined, then the TSC method could be calibrated for trap density. Essentially the same considerations hold for the transient-current methods (PITS and OTCS), as seen in Eq. (65). A further complication enters if eni and epi are of comparable magnitude, and ejepi is unknown [cf. Eq. (83)]. 

DC Transient-Current Method. In this method a step voltage is applied to the sample and the current response is measured by a fast-response electrometer. For the single- relaxation-time model, the current response would be given by equation (7-9). In recent years this method has been of renewed interest because with the advent of modem computing methods, it is possible to Fourier-transform the response in the time domain to obtain the frequency response. Several Fourier-transform dielectric spectrometers have been designed. We may note the one of historical significance due to Johnson et al.15, as well as modem commercial instruments.16 The method has the great... 

An alternative approach to decrease the time constant of electrochemical systems rests on the use of the miniaturized ITIES. Micron-scale ITIES use a micropipette to support the aqueous phase [98]. Subsequently an alternative approach, using micro-holes formed by laser ablation of thin polymer films, was reported [99]. The advantage of the micron-scale approach is that the radial diffusive flux to such an inlaid interface reaches a steady state, so the problems of transient current methods due to the double-layer charging constant are avoided. The low currents measured at such interfaces, due to their small size,... 

In most cases, the measurements are carried out isothermally in the frequency domain and the terms dielectric spectroscopy (DS) and dielectric relaxation spectroscopy (DRS) are then used. Other terms frequently used for DRS are impedance spectroscopy and admittance spectroscopy. Impedance spectroscopy is usually used in connection with electrolytes and electrochemical studies, whereas admittance spectroscopy often refers to semiconductors and devices. Isothermal measurements in the time domain are often used, either as a convenient tool for extending the range of measurements to low frequencies (slow time-domain spectroscopy, dc transient current method, isothermal charging-discharging current measurements) or for fast measurements corresponding to the frequency range of about 10 MHz - 10 GHz (time-domain spectroscopy or time-domain reflectometry). Finally, TSDC is a special dielectric technique in the temperature domain, which will be discussed in Section 2.2. 

In the transient voltammetric methods, one measures the characteristic parameters on transient polarization curves after some potential or current perturbation has been... 

The bulk of this review concerns transient experiments on heterogeneous catalysis at atmospheric pressure. After some comments on current methods for doing the experiments, the application of the method will be illustrated by two examples the oxidation of CO over Pt, and the hydrogenation of CO over Fe. 

Mager, S., Cao, Y. and Lester, H.A. Measurement of transient currents from neurotransmitter transporters expressed in Xenopus oocytes In Methods in Enzymology. 296, S.G. Amara, (ed.) p.551, Academic Press London, 1998. 

Juska G, Arlauskas K, Viliunas M, Kocka J (2000) Extraction current transients new method of study of charge transport in microcrystalline silicon. Phys Rev Lett 84 4946... 

For the development of SEU-hardened memory devices, it is expedient to reduce charge collected in a memory cell. For this purpose, the formation of buried oxide in device structures, i.e., the fabrication of SOI structure, is considered a useful method because such a buried oxide layer can be expected to suppress the charge collection due to the drift and funneling processes. However, no experimental approach had been made for the charge collection in SOI devices. To investigate the charge collection in the SOI structure, transient currents induced in SOI pn junctions by heavy ions such as 15-MeV carbon (C) or oxygen (O) ions have been measured. 

In [119], the hydrogen adsorption and desorption reactions in thin palladium electrodes were studied using the potential step method in order to analyze the mechanism of phase transformation. Transient current responses were recorded at the onset of the potential step for 47 pm thick Pd electrodes in 1 mol dm H2SO4 at ambient temperature. A model based on a moving boundary mechanism was proposed to account for the experimental i-t curves. It was found that the hydrogen adsorption reaction shows interfacial kinetic limitations and only numerical solutions can be obtained. Such kinetic limitations were not found for the desorption reaction and a semianalytical solution that satisfactorily fits the experimental data was proposed. 

The resemblance of the photocurrent to the optical adsorption spectrum has suggested the involvement of molecular excited states in the creation of charge carriers. While this resemblance is by no means universally observed, the concept of carrier creation via exciton interactions at or very near the illuminated electrode has become increasingly favored. Many of the data leading to these conclusions have been obtained by the use of pulsed light techniques (6, 7,3). These methods are virtually independent of electrode effects and the subsequent analysis of the transient current has led to considerable advances in the theory of charge transfer in molecular crystals. 

The transient current response of photo-electrodes to stepped-illumination changes suggests itself as a method of mechanistically interpreting this quantum efficiency problem. Though such transients have been studied for p-type GaP (1) and a number of n-type transition metal compounds (2, 3, 5, 6), published... 

Diffusion current is usually measured in the case of several transient electrochemical methods, e.g., in chronoamperometric and chronocoulometric experiments (see chronoamperometry, -> chronocoulometry, -> Cottrell equation) as well as it determines the shape of... 

The voltage-step method is, however, analogous to the TOF method and has been used in studies of semiconductive polymers. The theoretical transient current response is similar to that shown in the upper curve in Fig. 8.30(b). It rises from its initial value to a maximum and then falls away to a steady state... 

In the case of both reversible and irreversible electrode reactions, methods are now available for studying the steady-state and transient currents, and there has been much progress in the analysis of these currents in terms of the kinetic processes involved. 

In the treatment which follows, we assume that discharge of the doublelayer capacitance drives the reaction, and therefore use C = in Eq. (41). The effects of changes in coverage of the adsorbed intermediate are then taken into account by combining Eq. (41) with the kinetic equations for steps in the mechanism. In this method, no assumptions need then be made about the equivalent circuit or the nature of the pseudocapacitance, and the transient current during potential decay is not assumed to be equal to the steady-state current. The results then enable all three definitions of [Eqs. (46)-(48)] to be evaluated and compared, as illustrated in Fig. 10. 

In practice there are several limitations to such measurement. Obviously it implies that both members of the half-reaction are sufficiently stable for a cell to be realized. This is a serious difficulty in organic chemistry owing to usual great reactivities of the species formed upon electron transfers. For the most frequent cases it is then impossible to rely on reversible thermodynamic transformations to determine experimental values of standard reduction potentials. However, these important figures, or at least very precisely approximated values, can be obtained from current intensity potential curves or transient electrochemical methods as is discussed in a later section. 

As explained earlier, in transient electrochemical methods an electrical perturbation (potential, current, charge, and so on) is imposed at the working electrode during a time period 0 (usually less than 10 s) short enough for the diffusion layer 8 (2D0) to be smaller than the convection layer (S onv imposed by natural convection. Thus the electrochemical response of the system investigated depends on the exact perturbation as well as on the elapsed time. This duality is apparent when one considers a double-pulse potentiostatic perturbation applied to the electrode as in the double-step chronoampero-metric method. 

This paper describes some recently completed work on the electrical conductivity of paper. A reliable method of measuring bulk conductivity of paper, where the contact resistance is reduced to negligible values, has been developed. A study of the effect of some papermaking variables, such as the type of pulp, the degree of refining and the fiber orientation, on the bulk conductivity of paper is reported. Finally, an investigation has been made into the current transient phenomena exhibited by paper upon the application of an electric field. These transient currents were interpreted as the transport of ionic species within a water associated fibrous network making up the paper. 

A fundamental disadvantage of controlled-current techniques is that double-layer charging effects are frequently larger and occur throughout the experiment in such a way that correction for them is not straightforward. Treating data from multicomponent systems and stepwise reactions is also more complicated in controlled-current methods, and the waves observed in E-t transients are usually less well-defined than those of potential sweep i-E curves. 

One of the earliest applications of thermal transient spectroscopic methods to amorphous silicon was through the current DLTS measurements of R. Crandall (1980). Current DLTS measurements were carried out during the same period by Cohen et al. (1980b), and more recently by... 

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