Thermally stimulated current technique

For the characterization of the trap levels we applied the thermally stimulated current technique following the initial rise method [26] which was successfully applied to other conjugated polymers [27]. The device consisted of a sapphire substrate with an interdigital gold electrode structure on top of which a 200 nm thick polymer film was drop-cast. The gold electrodes had an overall length of... 

Aspects of common DEA techniques are presented in the following paragraphs, with emphasis on the instrumentation that is likely to be used in a typical thermal analysis laboratory examples are Novocontrol Spectrometers (BDS), TA Instruments (DEA 2970, although the production of this instrument has been discontinued), and Polymer Laboratories (DETA, this instrument is not available any more either). Dielectrometers (Micromet Instruments, now owned by Netzsch), used for in-process cure monitoring of thermosets, operate on similar principles. Features of the sensitive thermally stimulated current technique, and its comparison to DEA, are also discussed. 

Dielectric Depolarization Spectroscopy Thermally Stimulated Current Technique... 

K. Kawano and C. Adachi. 2009. Evaluating carrier accumulation in degraded bulk heterojunction oi anic soalr cells by a thermally stimulated current technique. Adv Funct Mater 19(24) 3934-3940. 

Faruque H S and Lacabanne C (1987) A thermally stimulated current technique for measuring the molecular parameters of Pebax, a polyether-block amide copolymer, J Mater Set 22 675-h78. 

Thermoluminescence and Thermally Stimulated Current Techniques References... 

In a similar fashion. Thermally Stimulated Current spectrometry (TSC) makes use of an appHed d-c potential that acts as the stress to orient dipoles. The temperature is then lowered to trap these dipoles, and small electrical currents are measured during heating as the dipoles relax. The resulting relaxation maps have been related to G and G" curves obtained by dynamic mechanical analysis (244—246). This technique, long carried out only in laboratory-built instmments, is available as a commercial TSC spectrometer from Thermold Partners L.P., formerly Solomat Instmments (247). 

It is also necessary to note that the success of TSR techniques to obtain information on trapping states in the gap depends on whether or not the experiment can be performed under conditions that justify equation (1.2) to be reduced to simple expressions for the kinetic process. Usually, the kinetic theory of TSR phenomena in bulk semiconductors—such as thermoluminescence, thermally stimulated current, polarization, and depolarization— has been interpreted by simple kinetic equations that were arrived at for reasons of mathematical simplicity only and that had no justified physical basis. The hope was to determine the most important parameters of traps— namely, the activation energies, thermal release probabilities, and capture cross section— by fitting experimental cnrves to those oversimplified kinetic descriptions. The success of such an approach seems to be only marginal. This situation changed after it was reahzed that TSR experiments can indeed be performed under conditions that justify the use of simple theoretical approaches for the determination of trapping parameters ... 

The presence of cooperative motion of chain segments present in intercalated polymer chains can be examined using various analytical techniques such as Differential Scanning Calorimetry (DSC), thermally stimulated current (TSC) and dielectric spectroscopy. DSC measurements on an intercalated PEO, (Mw= 100,000)/montmorillonite hybrid (20 wt. % polymer), indicated the absence of... 

Space-Charge-Limited Current, Thermally Stimulated Current, and Thermoluminescence and Isothermal Current-Decay Techniques... 

By thermally stimulated-current (TSC) techniques, Slowik (1976) measured a zero-field activation energy of 0.60 eV for PVK, slightly lower than the 0.65 eV reported by Gill (1972). The technique used by Slowik is based on an... 

Another way of investigating the depth in energy to which charges are trapped (a measure of the stability towards thermal decay) may be obtained by thermally stimulated currents (TSC). In this technique, electrodes on the two sides of the electret are connected via a sensitive current meter and the specimen is then heated at a constant, slow rate (1 Cmin-1, say). Discrete current peaks are observed as a function of temperature as successively more deeply trapped charges are released (Fig. 7.22). Dipolar relaxation may also give peaks in the TSC spectrum (van Turnhout, 1975). 

Thermally stimulated currents (TSC) have been used to probe the carrier generation mechanism in a dual-layer photoreceptor with an azo-pigment-based CGL and hydrazone-based CTL. It appears that this technique may be a useful tool in understanding the carrier generation process in organic photoreceptors [21]. 

For example, the most commonly used thermal method is and will almost certainly continue to be differential scanning calorimetry (DSC), hence here we have dedicated three chapters to the technique covering the principles, the optimal use of the method, and pharmaceutical applications. We then include chapters on thermo-gravimetric analysis, modulated temperature DSC, microcalorimetry, high sensitivity DSC, thermal microscopy, thermally stimulated current, and dynamic mechanical analysis, all of which have attracted great interest within the pharmaceutical field. In all cases, these chapters combine elements of theoretical background, measurement optimization, and pharmaceutical applications. It is our profound hope that in this way we will achieve a suitable mixture of depth, relevance, and accessibility. 

The techniques of thermally stimulated capacitance (TSCAP) and thermally stimulated current (TSC) are the simplest methods for surveying the... 

Cambridge University Press, Cambridge. A related technique, that of thermally stimulated current analysis is described by Ibar IP (1993) Fundamentals of Thermal Stimulated Current and Relaxation Map Analysis. SLP Press, New Canaan. 

In terms of modulated thermal analysis techniques , TMDSC clearly dominates the group. However, there is limited literature on temperature modulated thermogravimetic analysis (TMTGA) and temperature modulated thermomechanical analysis (TMTMA). Modulation principles have been applied to some less common thermal analysis techniques such as DMA and thermally stimulated current analysis and these developments will be briefly addressed here. It appears that the major development in thermal analysis in the next decade will be in the temperature modulated domain. 

Thermally stimulated current analysis (TSCA) is another member of the TEA group of techniques. In TSCA, the sample is subjected to a constant electric field and the current that flows through the sample is measured as a function of temperature. The mode of operation usually involves heating the sample to a high temperature under the applied field followed by quenching to a low temperature. This process aligns dipoles within the sample. The polarization field is then switched off and the sample is reheated and the current flow resulting from the relaxation of the induced dipoles back to the disordered state is monitored. 

G.P. Simon, A. Schonhals, Dielectric relaxation and thermal stimulated currents, in Polymer Characterization Techniques and Their Application to Blends, ed. by G.P. Simon (Oxford University Press, Oxford/New York, 2003), pp. 96-131 J. Skolnik, R. Yaris, Maciomolecules 15, 1041 (1982)... 

Relaxation-map analysis (RMA) n. A technique used on the results of a series of thermally stimulated current experiments in which the TSC data are transformed into relaxation times and plotted versus reciprocal absolute temperature to estimate enthalpy and entropy of activation for the molecular relaxations. 

The theory of dielectric relaxation is briefly summarized in another chapter Dielectric relaxation and dielectric strength of polypropylene and its composites in this book. The thermally stimulated current (TSC) technique is a special subclass of dielectric measuring methods. Nevertheless, because of its versatility and specific features, it is worth treating separately. 

Although the above approaches may all be amenable to detection of crystallization in finished products, they can also be used to characterize the HME (i.e., prior to downstream processing). Further, many other techniques are often applied exclusively to the HME intermediate. For instance, optical microscopy offers excellent detectability of crystalline material in transparent extrudates. Dielectric analysis (DBA Alie et al. 2004 Bhugra et al. 2007, 2008) and thermally stimulated current IR spectroscopy (Shah et al. 2006 Rumondor and Taylor 2010), atomic force microscopy (ATM Lauer et al. 2013 Marsac et al. 2012 Price and Young 2004), and calorimetric methods have also been used to detect crystallization from an amorphous matrix (Baird and Taylor 2012 Pikal and Dellerman 1989 Avella et al. 1991). 

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