Function Of Electric Field Strength Research Articles

Electrically Controlled Second-Harmonic Generation in Ferroelectric Liquid Crystal

The angularly phase-matched second-harmonic generation (SHG) in ferroelectric liquid crystal has been studied as a function of electric field strength, sample thickness, rotating angle and temperature. A sharp angular phase-matching curve of the SHG controlled by an electric field is observed even in the liquid crystal. The temperature dependence of the phase-matched SHG in the ferroelectric phase has also been studied, and the temperature-tuned phase matching of SHG is realized by using the change in tilt angle of the ferroelectric liquid crystal.

Tunnel ionization of donors in pure germanium

Abstract Transient currents due to field ionization of shallow donors at the liquid helium temperature are investigated in thin germanium samples by transient tunneling spectroscopy (TTS). The electron tunneling time from the antimony atoms to the conduction band has been measured as a function of electric field strength and compared with a simple scaled hydrogenic model.

Physical properties of carbon-black/polymer compounds

The conductivity of carbon-black/polymer compounds with a low percolation threshold has been studied as a function of electrical-field strength, carbon-black concentration, temperature, pressure and frequency. In addition ESR experiments have been performed. The results are compared with predictions of classical-percolation and tunneling models.

Ionization of liquid argon by x-rays: Effect of density on electron thermalization and free ion yields

Free ion yields were measured in liquid argon as a function of electric field strength at densities 736–1343 kg/m 3 (temperatures 149–195 K). The field dependence of the yields was parametrized using the extended Onsager and box models. Over the present density range the total ion yield was constant within 1% and was taken as 4.4, the average of earlier values at 87–91 K. The absence of internal vibrational modes in argon makes its electron thermalizing ability smaller than that of methane. The electron thermalization distance b GP in liquid argon is 3–5 times longer than that in liquid methane at a given d d c( d c = critical fluid density).

Kinetic theory of field evaporation of metals

Starting from adiabatic energy curves, calculated as a function of electric field strength we develop a perturbational method to construct diabatic states which form the basis to compute the temperature dependent ionization probabilities for field evaporation of metals. Employing a master equation we calculate the energy dependent ion yield as a function of field strength and temperature, and extract the field dependence of the activation barrier and the prefactor. As a function of field strength the activation barrier for field evaporation decreases monotonically for tungsten, whereas the prefactor increases up to a field strength of 4.5 VÅ for tungsten due to an increase in the ionization probability and then decreases due to changes in the surface potential.

Electron thermalization-distance distributions in electron-attaching fluids

The electron ejected from a molecule by an energetic impact moves away from the resultant ion and loses energy to the molecules with which it collides. The distance such electrons travel away from their ions during thermalization can be estimated by measuring the free-ion yields as a function of electric-field strength. This was done in gaseous and liquid carbon disulfide and hexafluorobenzene over wide ranges of densities. The electron thermalization-distance distribution in C6F6 was the same as that in most other liquids; it was a Gaussian distribution with a power tail. However in liquid CS2 the distribution was different, an exponential with a power tail, as in liquid nitrogen and liquid carbon monoxide. The different distributions reflect differences in the thermalization processes. The thermalizing ability of both CS2 and C6F6 is less in the liquid than in the gas. There is an especially sharp decrease in the thermalizing ability of CS2 at the highest densities.

Theory of field desorption and field ionization: Thermal field desorption of helium

Starting from adiabatic energy curves, calculated as a function of electric field strength we use a unitary transformation to construct diabatic states which form the basis to compute the temperature dependent ionization and neutralization probabilities for neutral helium and its single charged ion, respectively. Employing a master equation we calculate the energy dependent ion yield in thermal field desorption as a function of field strength and temperature.

Electron mobility in krypton dense gas as functions of electric field strength, temperature, and density

Electron mobilities μ were measured in dense gaseous krypton as a function of density normalized electric field E/n at 3.8≤n/1026 molecule m−3≤40 and 152≤T/K≤250. At each density a constant value of the mobility μ0 is attained at low E/n. At fields higher than a threshold (E/n)th μ first increased, passed through a maximum, and then decreased. In the saturated vapor nμ0 decreased with increasing (n,T) while at constant n, nμ0 increased with T. The density dependence of nμ0 is compared to the dielectric screening model of Baird [Phys. Rev. A 32, 1235 (1985)].

Electron thermalization distances and free ion yields in dense gases and liquids: Effect of molecular dipole moment

The effect of a molecular dipole moment on electron thermalization in X-irradiated fluids was examined by determining the effect of density on the density-normalized electron thermalization distance bGPd in dimethyl ether. Free ion yields were measured as a function of electric field strength at 0.06≤d/dc<2.7 (critical fluid density dc =271 kg m−3), and bGP values were obtained using an extended Onsager model. The permanent dipole increases the thermalizing ability of the fluid at all densities. However, the effect is smaller in the dense fluids and the transition from low-density gas behavior occurs at d/dc≊0.2.

Field adsorption of helium and neon on tungsten: An energy-resolved atom-probe study

The effect of an electric field on the interaction of He and Ne with tungsten surfaces in a field ion microscope is investigated using a retarding potential analyzer combined with a magnetic sector atom probe. Appearance-energy analysis and measurements of surface-temperature dependencies, especially of electron stimulated field desorbed He n+ and Ne n+ -yields, enable the determination of binding distances, vibration frequencies and desorption energies as a function of electric field strength. The He + yield generated by field ionization above a single surface site is measured as a function of time to determine the Ne field adsorption kinetics in the presence of He. Within the accessible field strength range of 3–5 V/Å, the He-W and the Ne-W bonds are considerably strengthened, in agreement with published atom-probe FIM results. A reduction of binding distances and an increase of vibration frequencies has been measured for He ads and Ne ads, which has not been observed before. This supports the tight binding cluster model of Kreuzer and Nath that suggests formation of a weak, field-induced chemisorption bond.

Electrohydrodynamic Flow in Thick Liquid Crystal Cells

ABSTRACTThe thermal transport across a thick (0.66 cm) liquid crystal cell has been measured versus applied ac voltage and frequency. These measurements are correlated with the optically observed onset of flow and turbulence in cells as identical as practicable to those used for the thermal transport measurements. In addition, the measurements are compared with reported observations in thin cells. The thermal transport across the liquid crystal is characterized by an effective thermal conductivity Kf. It was found that Kf increases with increasing frequency, at constant voltage, to a maximum enhancement at about 40 Hz at room temperature. Optical observations on thick cells indicate that dynamic columnar domains of flowing liquid crystal are the primary mode of heat transport, as determined by correlating the structure and characteristic lifetime of such domains as a function of voltage and frequency. Optical observations at low voltages suggest that Williams Domains do not exist in these thick cells, and that all observed responses are functions of electric field strength, not applied voltage (as in thin Williams Domain cells).

Electrostrictions in high-power soliton generator

Electrostriction effects are considered in a high power dielectric loaded transmission line designed to generate solitons. The Čerenkov emission of elastic waves from the metal-dielectric interface produces the largest strain among the strain producing mechanisms. The expression for strain as a function of electric field strength is found. The signal loss due to the emission of elastic waves is shown to be insignificant.

Electron thermalization distances and free ion yields in dense gases and liquids-effects of molecular structure

Radiolysis free ion yields were measured as a function of electric-field strength in vapor/liquid equilibrium fluids of ethene, propene, cyclopropane, propane, n-butane and i-butane at 0.15<or=d/d/sub c/<3(d/sub c/=critical fluid density). From these yields, secondary electron thermalization distances b/sub GP/ were estimated using the extended Onsager model. In the normal liquid at d/d/sub c/>1.5, the effects of molecular shape gave b/sub GP/d in methane>i-butane>ethane>propane>n-butane. The effect of pi -bonding gave n-butane>cyclopropane>ethene approximately propene; the permanent dipole of propene had negligible effect in the dense liquid. The conduction-band energy in supercritical fluids of n-butane, isobutane, n-pentane and isopentane was measured as a function of the fluid density. The conduction-band energy values in these fields show a density dependence that is related to their molecular structure. The correlation between the density dependence of conduction-band energy and of electron mobility is discussed in terms of the deformation potential theory.<<ETX>>

Electron mobility in dense gases of deuterated methanes as functions of electric field strength, temperature, and density

Values of electron mobility μ were measured in gaseous deuterated methanes CHxD4−x(x=0–4) as a function of density normalized electric field strength at 0.2≤n/1026 molecule m−3≤61=nc (subscript c denotes critical fluid), and 98≤T/K≤433. The mobility at low E/n had a constant value μ0 but at fields above a threshold (E/n)th, μ increased. In the saturated vapor the ratio of the electron drift velocity at (E/n)th to the speed of sound in the vapor was determined mainly by T, while nμ0 was mainly determined by n; there was no clear isotope effect. The effect of density on nμ0 is discussed in terms of the deformation potential and dielectric screening models. The former fits better.

Time-resolved reflection spectrum of ordered structure of monodispersed polystyrene spheres in an electric field

Electrically induced changes in lattice structure have been studied by time-resolved reflection spectrum measurements of monodispersed polystyrene latices (diameter 91 nm) in deionized solution. The reflection spectrum peak shifts to longer or shorter wavelengths depending on the polarity of the electric field. The transformation of the lattice structure on applying a voltage has at least two relaxation times. Fast and slow steps correspond to the structural relaxation and the relaxations of grain boundaries or crystallites, respectively. The Young's modulus of the crystallites is evaluated as 62 dyn cm–2 from the magnitude of the shift as a function of electric-field strength. The results support the idea that the electrostatic intersphere repulsion in the effective hard-sphere model is essential for the ordering.

Investigations of the nonlinearity of permittivity of a triglycine sulphate crystal above the curie temperature

From measurements of variations of permittivity as a function of electric field strength for various temperatures in the vicinity of Tc in the paraelectric phase, values were found for the critical exponents γ0 = γ = 0.95 ± 0.05, γ2 = 4.0 ± 0.2 and γ4 = 6.8 ± 0.5 in the temperature relations α2n = A2nτ-γ2n, where α2n are the coefficients in the expansion of the series for permittivity as a function of electric field, i.e. e = α0 + α2E2 + α4E4 + ···. The values of gap exponents Δ4 = 1.5 ± 0.1 and Δ6 = 1.4 ± 0.2 were determined. It was also confirmed that there is good agreement as to the order of the amplitude ratios A2:A0 and A4:A2.

Dielectric behavior of polyelectrolytes. IV. Electric polarizability of rigid biopolymers in electric fields.

The equilibrium Kerr effect of a system of mobile charges constrained to the surface of biomacromolecules is calculated. Cylindrical and spherical geometries are considered. For the cylinder we determine the anisotropy of electric polarizability as a function of length, temperature, and number of charged species in the low-field regime, and the fraction of the maximum induced dipole in the field direction for higher electric fields. The results are compared to experimental data for DNA oligomers taken from the literature. With spherical geometry we calculate the fractional induced dipole moment as a function of electric field strength and from this deduce the orientation function. The field dependence of the orientation function is compared to experimental data in the literature for bovine disk membrane vesicles.

Distorted-wave calculations of dielectronic recombination as a function of electric field strength.

The effects of external electric fields on dielectronic recombination have been studied in the distorted-wave approximation. The eigenvectors for the doubly excited Rydberg states were determined by diagonalizing a Hamiltonian matrix which includes the internal electrostatic and spin-orbit terms, as well as the Stark matrix elements. Calculations were performed for the dielectronic recombination transitions associated with the 2s..-->..2p excitation in the Li-like ions B/sup 2 +/, C/sup 3 +/, and O/sup 5 +/; and the 3s..-->..3p excitation in the Na-like ions P/sup 4 +/, S/sup 5 +/, and Cl/sup 6 +/. The results for the Na-like ions are compared with recent merged-beam measurements, and the differences between the two sequences with respect to the enhancement of dielectronic recombination as a function of electric field strength are discussed.

ChemInform Abstract: FIELD DEPENDENCE OF THE PHOTOIONIZATION CURRENT FROM N,N,N′,N′‐TETRAMETHYL‐P‐PHENYLENEDIAMINE IN THE PRESENCE OF AN ELECTRON SCAVENGER

The photocurrent from TMPD in 2,2,4-trimethylpentane (isooctane) excited at 213.8 nm was measured as a function of electric field strength (to approx. = to 170 KV/cm) and, at each field strength, as a function of the concentration, c, of n-perfluoroheptane (to 0.61 M). The form of the field dependence confirms that the perfluorocarbon acts to somehow reduce the spatial extent of the distribution function of initial separation distances of the geminate pair. The field dependence can be well fitted to the Onsager theory with distribution functions of the form f(r)r/sup 2/ dr = (..cap alpha../sup n + 1/ /nexclamation)r/sup n/e/sup -ar/ dr with n = 1, 2 in both the presence and absence of perfluorocarbon. The dependence of ..cap alpha.. on c is discussed; a conclusion is drawn that the most satisfactory distribution function of the exponential form for describing both the concentration dependence and the field dependence of the photocurrent is obtained with n = 2. 9 references, 3 figures, 1 table.

Field dependence of the photoionization current from N,N,N',N'-tetramethyl-p-phenylenediamine in the presence of an electron scavenger

The photocurrent from TMPD in 2,2,4-trimethylpentane (isooctane) excited at 213.8 nm was measured as a function of electric field strength (to approx. = to 170 KV/cm) and, at each field strength, as a function of the concentration, c, of n-perfluoroheptane (to 0.61 M). The form of the field dependence confirms that the perfluorocarbon acts to somehow reduce the spatial extent of the distribution function of initial separation distances of the geminate pair. The field dependence can be well fitted to the Onsager theory with distribution functions of the form f(r)r/sup 2/ dr = (..cap alpha../sup n + 1/ /nexclamation)r/sup n/e/sup -ar/ dr with n = 1, 2 in both the presence and absence of perfluorocarbon. The dependence of ..cap alpha.. on c is discussed; a conclusion is drawn that the most satisfactory distribution function of the exponential form for describing both the concentration dependence and the field dependence of the photocurrent is obtained with n = 2. 9 references, 3 figures, 1 table.