Polariton dynamics of a bounded weak ferromagnet in an external dc electric field tangential to the interface

Using the example of a semibounded easy-plane weakly ferromagnetic crystal, magnetized tangentially to its surface, the conditions have been determined under which, with the application of an external dc electric field along the easy-magnetization axis, a number of anomalies arise at the transmission and localization of OA and TM electromagnetic waves through the interface between a nonmagnetic dielectric and a weak ferromagnet due to quadratic magneto-optical interaction.     

Crystallization of a germanium melt in an external electric field

Data are presented on experimental studies of the influence of an external electric field on crystallization of a germanium melt under the layer of a B₂O₃ flux. It has been found out that with the field supercoolings of the melt sharply change. This effect is due to the change of the number of active nucleation centres at the germanium – B₂O₃ flux interface. The maximum supercoolings of the germanium melt ΔT⁻ = 190 K were obtained when a negative potential was connected to germanium. The dependences of supercooling on preliminary melt overheating were measured.     

Crystallization of proteins under an external electric field

An external electric field affects the crystallization of proteins when applied under some conditions of temperature, pH, and precipitating agent composition. As suggested in the theoretical part of this paper, it produces large protein concentration gradients inside the mother liquor leading to a local supersaturation area in the crystallization solution. Such an experiment has been used for the first time on the crystallization of a protein. The effects of an external electric field on the crystallization of hen egg-white lysozyme at 293 K, pH 4.5, and two NaCl concentrations (0.6–0.7 M) have been investigated using the vapor diffusion method. The application of electric field results in a smaller number of crystals with larger size. The crystals grew at the droplet surface, near the cathode. The nucleation rate is drastically reduced and this experimental method could be used to control the number of crystals in the droplet.     

Theoretical description of the external electroluminescence around a single dislocation oriented perpendicular to the surface

Under the assumption that a dislocation decorated by impurities can be described as a macroscopic inhomogeneity the radial distribution of the flux of photons around a dislocation is calculated, where the internal absorption of the luminescence is taken into account in addition to the effect of the surface. The theoretical results are used to compute simulated images for different values of the radiative lifetime inside the dislocation region.     

Nucleation rate enhancement of porcine insulin by application of an external AC electric field

The nucleation rate of porcine insulin increased under application of an external AC electric field at 3 MHz. This is attributed to the electrostatic energy added to the chemical potentials of both the liquid and solid phases; the chemical potential of the solid was significantly changed compared with that of the liquid, which lead to an increase in the driving force for nucleation. Therefore, application of an external AC electric field can be a useful technique for protein crystallization.     

Effect of various precipitants on the nucleation rate of tetragonal hen egg-white lysozyme crystals in an AC external electric field

It was observed that the effect of an external electric field on the nucleation rate of tetragonal hen egg-white lysozyme crystals varied depending on the precipitant used (NaCl, NiCl₂ or YbCl₃) and that the electric double layer (EDL) played an important role in generating an external electric field of the necessary strength to control the nucleation rate. This phenomenon depended on the ionic strength of the precipitant used; that is, a precipitant of greater ionic strength resulted in a thinner EDL and increased the effect of the external electric field as the driving force for nucleation. The dependence of the nucleation rate on the precipitant was attributed to the magnitudes of the external electric fields generated in EDLs of varying thickness which were formed in the presence of different precipitants.     

Theory and computer simulation of the reflection and refraction of bulk acoustic waves in piezoelectrics under the action of an external electric field

The basic equations describing the conditions for reflection and refraction of bulk acoustic wave at the interface between acentric crystals subjected to the action of a uniform external electric field are reported. Numerical analysis of the effect of this field on the reflection and refraction anisotropy of bulk acoustic waves at the crystal/vacuum and piezoelectric/elastic-isotropic-medium interfaces is performed.     

Formation of unusual nonferroic domains in TeO2 single crystals under external electric field

The formation of unusual slowly relaxing domains under an external dc electric field has been revealed in paratellurite (TeO₂) crystals. These domains differ from those arising in ferroics (ferromagnets, ferroelectrics, ferroelastics, etc.). The effect is characterized by the existence of a threshold field strength (at which domains begin to be formed) and long equilibrium settling times (up to a few hours, depending on the electric field strength). A crystal returns to the initial single-domain state also after a few hours after the field is switched off. High-resolution triple-crystal X-ray diffractometry has revealed that domains retaining the paraelastic tetragonal phase rotate with respect to each other in space without changing their lattice parameter. The domain sizes are 2–4 mm, depending on the field strength. Currently, the exact mechanisms of domain formation are unclear. Possible reasons for the formation of these defects and an analogy of the observed effects with the behavior of liquid crystals under electric field are discussed.     

Propagation of elastic waves near acoustic axes in crystals under the action of extreme external forces: I. Piezoelectric crystal in an electric field

The directions of an external electric field at which extreme changes occur in the difference in the velocities of elastic waves propagating along the initial acoustic axis in a piezoelectric medium of arbitrary symmetry are theoretically determined. The problem of degeneracy in an external electric field is considered for elastic waves propagating in a given direction from the vicinity of an initial acoustic axis. The extreme electric fields and corresponding changes in the characteristics of transverse waves are calculated by the example of the behavior of acoustic axes in Bi₁₂GeO₂₀, Bi₁₂SiO₂₀, La₃Ga₅SiO₁₄, and LiNbO₃ crystals.     

Time evolution of cholesteric fingers of the second species in an electric field

Different growth modes of isolated cholesteric fingers of the second species (CF‐2) in an electric field at voltages near a coexistence line (V₂) between cholesteric and nematic mesophases are in detail described. Videomicroscopy and computer image analysis were used for investigation of the pattern in polarized light. It is shown how a drift, a lengthening and a shape of fingers depend on the voltage at which the growth sets in and three typical scenarios are distinguished. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optimization of the calculation of a local electric field in crystals by the transient-region method

The specific features of using the method of transient-region for calculating local electric fields and the corresponding potentials are considered on examples of the calculations for NaF, CsCl, and LiNbO₃ crystals. It is shown that for crystals with a primitive cubic lattice, this method can provide any given accuracy of the calculated Madelung constant; for displacive-type ferroelectrics (LiNbO₃), the method allows the calculation of the local electric field with a very high accuracy. It is emphasized that for each specific object, one has to carefully select the parameters of the convergence function.     

Propagation of elastic waves near acoustic axes in crystals under the action of extreme external forces: II. Centrosymmetric crystal in an electric field; III. Crystal under mechanical stress

The problem of degeneracy of elastic waves propagating in the vicinity of acoustic axes in centrosymmetric crystals in an external electric field and in crystals with arbitrary symmetry under uniaxial mechanical stress is considered. For the case of acoustic axes coinciding in the absence of external forces with the symmetry axes, equations describing the directions of external forces at which the difference in the velocities of initially degenerate transverse waves or angles of splitting and shift of the initial degeneracies reach maximum values are obtained. By the example of acoustic axes in LiNbO₃, La₃Ga₅SiO₁₄, Bi₁₂SiO₂₀, and SrTiO₃ crystals, extreme directions of uniaxial mechanical stress and the corresponding changes in the characteristics of transverse waves are calculated. The behavior of acoustic axes under uniaxial compression is analyzed.     

The electric field gradient in a random packing model of amorphous ionic materials

The electronic field gradient distribution at both the cation and anion sites has been computed for a dense random packing model of amorphous FeF₃ and analysed with particular reference to the sign of the principal component q. For the (large sphere) anion components twice as many sites are found with q>0 as with q<0 and the distribution of asymmetry parameter η is quite anomalous for the sites with positive q. These unusual features, and their essential absence at the (small sphere) cation sites, can be understood in terms of the local coordinations of the two types of ionic constituent and are likely to remain at least qualitatively valid for majority anions and minority cations in a wider context of amorphous ionic materials.     

Crystal growth of InN by MOCVD with electric field along the c-axis

We report on physical properties of InN grown by metalorganic chemical vapor deposition (MOCVD) with electric field applied along the c-axis. The electric field is applied continuously from the growth of the low temperature InN buffer layer to the procedure of cooling down to room temperature. As a result, the crystal morphology degrades, c-lattice constant elongates by 0.12% at ±1 kV/cm, Hall mobility decreases, and the phonon vibration along the c-axis broadens, which suggests that the physical properties of InN can be controlled by the electric field applied along the c-axis during the crystal growth.     

The impurity heterogeneities in the surface layer of silicon with an atomically clean surface

The electrical and photoelectrical properties of the surface region of silicon after evaporation in vacuum used in obtaining an atomically clean surface at the subsequent epitaxy are studied. The formation kinetics of a p-layer at 1300 and 1350 °C for the heating time of 10 to 10³ s is investigated. The effective values of holes mobility in p-layers are independent on a decrease of layer thicknesses down to 0.2μm at the concentration of acceptors of 10¹⁷ to 10¹⁸ cm⁻³ (294 K). The concentrations of doping impurities in the surface region of silicon before and after thermal treatment are determined by the method of mass-spectrometric analysis. The peculiarities of transport and building-in of doping impurities of the III and V groups at epitaxy and the possible nature of acceptor levels are discussed. A concentration profile of acceptors and donors from the surface deep into the silicon bulk is determined by the methods of layer-by-layer etching and of C-V characteristics. An effective built-in electric field is due to acceptor and donor distribution, which favours drift separation of minor radiation-generated current carriers in the p-n structure. The high-sensitive and fast-responding photoreceivers have been produced. The given detectability reaches 2 × 10¹² cm Hz^1/2/W at a wavelength of 1.06μm.     

Formation of quasi-ordered structures on the surface of strontium titanate in a plasma field

The X-ray diffraction and X-ray spectroscopic properties of strontium titanate single crystals and their surface exposed to plasma have been investigated. Both undoped SrTiO₃ crystals and crystals containing impurity ions of the iron or lanthanum groups have been analyzed. Data on the plasma-induced formation of ordered crystallites on the sample surface were obtained by electron and atomic force microscopy. The crystallites are from 10^?7 to 10^?9 m in size and their hypothetical orientation [321] is independent of the sample orientation and irradiation dose.     

Influence of magnetic field on the director profile in nematic layer with curved surface

A nematic liquid crystal layer with a curved upper boundary exposed to a magnetic field directed along the layer plane has been studied. Strong nematic anchoring at the lower boundary surface is assumed. A phenomenological expression for the director profile is proposed to solve the problem on the director profile distribution in this system and its stability with respect to the rotational deformations in relation to the degree of the upper-surface roughness and the magnetic field value. The distribution parameters are found by optimizing the expression for the free energy of the liquid crystal system.     

The use of an electric analogue to solve the lamellar eutectic diffusion problem

An electrical analogue technique has been developed to obtain numerical solutions to the diffusion equation in the liquid ahead of a growing lamellar eutectic. Using the solutions it has been possible to examine certain of the approximations made in earlier treatments of the problem. A modification has been made to the Jackson and Hunt model of eutectic growth which becomes important when composition differences in the interfacial liquid composition become large (i.e. at very high growth velocities). The modified treatment no longer predicts υλ² = constant although the variation of υλ² with growth velocity is not likely to be detected easily.     

Specular reflection of X-rays under the conditions of grazing diffraction in a crystal with an amorphous surface layer

Specific features of the anomalous angular dependence of the specular-reflection intensity under the condition of noncoplanar grazing X-ray diffraction in a crystal coated with an amorphous surface film were revealed and studied experimentally. The phenomenon was analyzed theoretically and its high sensitivity to the presence and the thickness of a several-nanometer-thick amorphous film was shown. The experimental data were used to determine the thickness and the density of a native oxide layer formed on the surface of a silicon single crystal.