Application-related Aspects of Dielectrics

Because of the complexity of the relationships between the properties of the gate dielectric and the performance of organic TFTs and ICs it may be useful to explain 

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Solvent permittivity — is an index of the ability of a solvent to attenuate the transmission of an electrostatic force. This quantity is also called the -> dielectric constant. -> permittivity decreases with field frequency. Static (related to infinite frequency) and optical op (related to optical frequencies) permittivities are used in numerous models evaluating the solvation of ions in polar solvents under both static and dynamic conditions. Usually the refractive index n is used instead of op (n2 = eop), as these quantities are available for the majority of solvents. The theory of permittivity was first proposed by Debye [i]. Systematic description of further development can be found in the monograph of Frohlich [ii]. Various aspects of application to reactions in polar media and solution properties, as well as tabulated values can be found in Fawcetts textbook [iii]. 

Proton tautomerism in the solid state has drawn attention from the aspect of application as well. Further investigations in related areas, such as photochromism, thermochromism, photochemical hole-burning and hydrogen-bonded dielectrics, may open a horizon of protonic molecular devices. 

Various aspects of the use of PCHE and related materials as a dielectric layer in capacitor films has been described and patented by several workers [72,73]. The material properties that are important for this application are low moisture absorption (which allows for the formation of thin films with minimal pinhole formation), a high heat distortion temperature, and high breakdown voltage. 

The coupling of microwave energy and a medium depends on the dielectric properties of the substance [198]. This can be measured by the dielectric coefficient Sr, a characteristic for each substance and its state. The dielectric coefficient relates to the capacitance C. The aspects of technical applications of microwaves in chemical reactions and scale-up are discussed in more detail by Nuchter and colleagues [199]. 

Initially, electrochemical methods were restricted to rather conducting media (solvents with large dielectric constants, large ionic strength), because of problems related to a precise control of an electrode-solution potential difference. Since the rapid development of ultramicroelectrodes in the past decade, this is no more the case, and electrochemistry in solvents of low dielectric constants (arenes, alkanes,efo) or in the absence of deliberately added electrolytes is feasible routinely. Both the theoretical and experimental aspects of such unconventional electrochemistries are now well mastered and the techniques ready for use and application. We have no doubt that the breaking of these historical frontiers of electrochemistry will allow a rich harvest of mechanistic studies performed under conditions that may now approach those used in homogeneous reactions and in catalysis. 

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