High electric field

Only at extremely high electric fields are the water molecules fiilly aligned at the electrode surface. For electric fields of the size normally encountered, a distribution of dipole directions is found, whose half-widtli is strongly dependent on whether specific adsorption of ions takes place. In tlie absence of such adsorption the distribution fiinction steadily narrows, but in the presence of adsorption the distribution may show little change from that found at the PZC an example is shown in figure A2.4.10 [30]. 

Highly protective layers can also fonn in gaseous environments at ambient temperatures by a redox reaction similar to that in an aqueous electrolyte, i.e. by oxygen reduction combined with metal oxidation. The thickness of spontaneously fonned oxide films is typically in the range of 1-3 nm, i.e., of similar thickness to electrochemical passive films. Substantially thicker anodic films can be fonned on so-called valve metals (Ti, Ta, Zr,. ..), which allow the application of anodizing potentials (high electric fields) without dielectric breakdown. 

The rapid application of a very high electric field (lifl lO V cm can perturb chemical equilibria. This effect is described by tire thennodynamic relation... 

Field desorption. The formation of ions in the gas phase from a material deposited on a solid surface (known as an emitter) that is placed in a high electrical field. Field desorption is an ambiguous term because it implies that the electric field desorbs a material as an ion from some kind of emitter on which the material is deposited. There is growing evidence that some of the ions formed are due to thermal ionization and some to field ionization of material... 

Field ionization. The removal of electrons from any species by interaction with a high electrical field. 

In contrast to the LEDs, electroluminescent phosphors operate under high voltage and very high electric fields. The Sharp devices are ac and purely... 

MaxweU-Boltzmann distribution. At high electric fields, E > 10 kV/cm, no longer increases with electric field and approaches a limiting saturation speed, determined primarily by optical phonon emission. Eigure 3 shows the variation of drift speed with electric field for electrons and holes in various semiconductors. 

The apphcation of a high electric field across a thin conjugated polymer film has shown the materials to be electroluminescent (216—218). Until recentiy the development of electroluminescent displays has been confined to the use of inorganic semiconductors and a limited number of small molecule dyes as the emitter materials. Expansion to the broad array of conjugated polymers available gives advantages in control of emission frequency (color) and facihty in device fabrication as a result of the ease of processibiUty of soluble polymers (see Chromogenic materials,electrochromic). 

Heat, kT High electrical field, F Mechanical force... 

A few techniques, one or two of which are important, cannot be classified according to the nature of the exciting particle, because they do not employ primary particles but depend instead on the application either of heat or a high electric field. These techniques are listed in Tab 1.2. 

Oxide films formed at low temperatures are initially continuous and amorphous, but may undergo local crystallisation with the incorporation of the oxide islands , a process that is facilitated by water, heat, high electric fields and mechanical stress... 

Figure 12-7. j(F) characteristics for a 100 mu thick film of diphciiyluininosiyrylheiucue (DASMB) sandwiched belween ITO and Al-eleclrudcs, paraniciric in temperature. The saturation at high electric fields is due to the resistance of the ITO. 

The reason for the success of this type of data fitting is that for moderately large barriers it becomes unimportant whether escape for the image potential is treated within the framework of the Onsager or the RS model. An indication that the Onsager description is, nevertheless, more appropriate is the intersection of j(/ ) curves for variable temperature at high electric fields. This is a characteristic feature of Onsager processes 24J. 

A phase transition can be induced also by a high electric field. This is, for instance, the case of the conversion of the non polar a form (form II) of PVDF to the polar 8 form (form lip) [31] (see Sect. 2.3). 

Interesting phenomena are observed by increasing the concentration of reversed micelles, changing the temperature or pressure, applying high electric fields, or adding suitable solutes, In some conditions, in fact, a dramatic increase in some physicochemical properties has been observed, such as viscosity, conductance, static permittivity, and sound absorption [65,80,173,233,243,249,255,264-269],... 

In Section II, the basic equations of OCT are developed using the methods of variational calculus. Methods for solving the resulting equations are discussed in Section III. Section IV is devoted to a discussion of the Electric Nuclear Bom-Oppenhermer (ENBO) approximation [41, 42]. This approximation provides a practical way of including polarization effects in coherent control calculations of molecular dynamics. In general, such effects are important as high electric fields often occur in the laser pulses used experimentally or predicted theoretically for such processes. The limits of validity of the ENBO approximation are also discussed in this section. 

For polycr5rstalline piezoceramics to work, the electrically charged dipoles within the entire piezoelectric component must be aligned by placing the piezoceramic within a high electric field—a process known as poling. The ability of piezoceramics to almost instantaneously convert electrical... 

---