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.     

Crystallization of amorphous germanium films

Kinetics of isothermal crystallization has been studied in the temperature range from 375 to 525°C. The kinetic curves are obtained and the rate of isothermal transformation of amorphous films into crystalline ones has been determined. Using experimentally determined kinetic curves the stability diagram of the amorphous films has been plotted in the temperature range from 400 to 525°C. The value of effective activation energy has been defined.     

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.     

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.     

Polariton spectrum of a bounded antiferromagnet with a center of antisymmetry in an external electric field oriented normally to the surface

The features of transmission of TE and TM polaritons through an interface between magnetic and nonmagnetic media and their localization at the interface in an external dc electric field have been studied. This field is directed along the hard magnetization axis. The magnetic medium is an easy-plane tetragonal antiferromagnet; it is odd with respect to inversion. A magnetic plate and a 1D magnetic photonic crystal in an external dc electric field, oriented normally to the interface, are considered.     

Crystallization of binary melt with a periodically varying rate

The time dependence of the crystallization rate at crystal pulling to the cold zone with a velocity that has a sinusoidal component has been investigated within a one-dimensional time-dependent model of solidification of a diluted binary melt by the net method. It is shown that the regularities that were obtained previously by the analytical method for pulling rates with small oscillations are repeated in many respects when considering oscillations of larger amplitudes. At significant oscillation amplitudes, the time-averaged values of impurity concentration at the interface for the stationary and vibrational crystallization modes may differ by several dozen percent.     

High field effects in amorphous germanium

Measurements of high field current have been made on amorphous Ge (a-Ge) films over the temperature range from 100 to 300 K. Non-ohmic conduction in a-Ge occurs at electric fields greater than 1–2 × 10⁴ V/cm. Field dependence of the conductivity has been explained in terms of the enhanced emission probability of carriers from the screened coulombic trap centers. Assuming the optical dielectric constant for a-Ge films, the screening length of the trap centers and the density of states at the Fermi level are estimated to be 12 Å and ～6.1 × 10²⁰ cm^?3 eV^?1, respectively.     

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.     

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.     

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.     

Crystallization of inorganic salts from aqueous solutions in a microwave field

The crystallization of some inorganic salts (KH₂PO₄, NaCl, Sr(NO₃)₂, KNO₂, Ca(OH)₂) by the thermal-gradient (with decreasing temperature) and solvent-evaporation methods using microwave heating of solutions is investigated. It is established that the growth rates of single crystals in a microwave field are an order of magnitude higher than obtained in other known techniques at comparable crystallization temperatures and supersaturations. For example, the growth rate of prismatic faces {100} of KH₂PO₄ crystals is as high as 11 mm/day at supersaturations of ～1.2%. The results obtained are discussed in the context of the effect of microwave radiation on the adsorption surface layers of crystals. Fine-grained phases of the salts under study are obtained by evaporation of the solvent.     

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.     

Crystallization of beryllian indialite from its own melt under oxidizing conditions

It is established that beryllian indialite (ideal formula Mg₂BeAl₂Si₆O₁₈) is formed spontaneously under oxidizing conditions in a wide range of relatively high cooling rates at small overheatings of its own melt and short overheating times. The significant difference in the growth rates of the prism and pinacoid faces of beryllian indialite from its own melt (0.08 and 0.40 mm/h, respectively) obtained by the Steber method is explained by the fact that the prism grows according to the tangential mechanism, while the pinacoid grows in the normal way. The face effect in these crystals manifests itself in the enrichment of the prism with beryllium and silicon as opposed to pinacoid.     

Instability of the melt flow in VGF growth with a traveling magnetic field

The linear instability of a thermally stratified melt flow in the VGF configuration driven by a traveling magnetic field (TMF) is considered numerically and experimentally. The dependency of the instability threshold on the governing parameters is found for several cuts through the parameter space covering a wide range of possible applications. In a first approximation the linear instability occurs when the dimensionless TMF forcing parameter reaches the magnitude of the Grashof number. This is particularly true in a medium-sized crucible where the first instability is axisymmetric and sub-critical. As the Grashof number increases the flow develops self-similar boundary layers and the instability becomes three-dimensional. The instability originates in the bottom boundary layer where the convection tends to suppress the imposed temperature gradient in the central part of the melt zone. It is shown that the TMF may serve as a tool to control the phase interface shape without causing flow instationarity when the crucible diameter exceeds a certain value. This value is estimated to be around 6 cm for GaAs. The flow stays stable if the TMF is used for a reversal of the meridional flow with the aim to remove a possible dopant concentration peak on the axis.     

Crystallization kinetics of lithium niobate films from limited volume of melt solution

The growth kinetics of LiNbO₃ films from a limited volume of melt solution is observed. We developed crystallization models describing the character of mass transfer in the liquid phase for isothermal and non-isothermal epitaxy. Analytical expressions have been derived connecting the film thickness with the system growth parameters. The experimental values being in good agreement with the calculated ones.     

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)     

X-ray diffraction study of crystals under a static electric field

This paper gives an overview of the effect of electric field on the diffracted intensity and contrast on the X-ray topographs recorded from crystals of non-linear and electro-optic materials, ionic conductors, semiconductors, insulators and ferro-electric materials. Application of a dc electric field gives rise to a change in the diffracted intensity by several orders of magnitude and contrast on the topographs. The effect is illustrated with examples of -LiIO₃, KTiOPO₄, LiN₂H₅SO₄, KNbO₃, LiNH₄SO₄, quartz, silicon etc. and the mechanism for it is discussed.     

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.     

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.     

Simulation of mass transfer in a kinetic experiment based on migration of flat layers of a solution in a melt in a temperature gradient field

Mass transfer upon migration of flat liquid layers of a solution in a melt under conditions of slow change in the average temperature at a constant rate has been analyzed for the dislocation and nucleation mechanisms of interface processes. It is shown that the experimental data on the dependence of the migration rate of flat layers on their thickness can be adequately described within the theory developed for strictly steady thermal conditions. A technique is proposed for determining the overall limitations on the mass transfer at interfaces and the migration rate in the diffusion mode from the experimental results obtained in a mixed migration mode.