Evaluation of the ion drift parameters in dielectric films from the dynamic current-voltage characteristics

The nonequilibrium dynamic current-voltage characteristics of the MDM structure are analyzed on the basis of the exact numerical solution of the electrical transport equations with consideration of the drift and diffusion of the charge carriers in an electrically neutral dielectric with blocking electrodes. A new method is proposed for the evaluation of the charge carrier mobility from the position of the current maximum on the dynamic current-voltage characteristic curves. The role of the diffusion component of the current is evaluated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 87–94, January, 1984.     

Calculation of the diffusion coefficient in crystals

The diffusion coefficient for vacancies is calculated on the basis of the Kubo formula. Here no assumptions are made about the character of the migration of the atom into the vacant site, and the calculation is carried out on the basis of a Hamiltonian proposed earlier by the author. A general expression is obtained for the temperature dependence of the diffusion coefficient that is valid in a wide temperature range. The case T » T_D (T_D is the Debye temperature) is especially analyzed, where the diffusion process is in the main connected with over-barrier jumping. The corresponding temperature dependence is determined by the expression T^3/2exp (–U/_BT, where U is the height of the potential barrier that separates neighboring sites. The dependence of the diffusion coefficient on the mass of the diffusing atom is also investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 60–65, June, 1985.     

Superlinearity of current-voltage characteristics of oxidized cholesterol bilayer membranes

Current-voltage characteristics of bilayer oxidized cholesterol membranes were measured in 0·1 M KCl solution. The ohmic conductance was (5±3) × 10^–4–1 m^–2. To explain the superlinearity of the characteristics, a model of the ion transport through transient pores was used. Alternative diffusion barrier models could also explain the nonlinearity, but the distribution coefficients of permeable ions between the membrane hydrocarbon phase and the aqueous phase had to be taken unreasonably high.     

Low-temperature diffusion of phosphorus in silicon

Nontrivial mechanisms of low-temperature diffusion of impurities in solids have been discovered recently. We studied accelerated diffusion of phosphorus in a single crystal of silicon, which takes place during decomposition of an over-saturated inhomogeneous solid solution. A thin (1.5–2 m) doped layer was formed by low-temperature diffusion from the gas phase. The distribution profile, which was determined by the method of differential conductivity, shows that heat treatment at 550°C leads to a decrease in the donor concentration in the subsurface region and to the impurity movement into the bulk of the sample. The diffusion coefficient has been calculated on the computer using experimental data, and in the range between 400°C and 700°C has been represented by the Arrhenius equation. The value of the frequency term is equal to 3.7·10^–6 cm²/sec, and the value of the activation energy is 1.81 eV. The presented results have been analyzed, as well as the data obtained from the measurements on carrier mobility (using the Hall effect) and the parameters of the crystal lattice (using the method of asymmetric double crystal x-ray spectrometer). A physical model for the dissociation diffusion is proposed, which is controlled by the decay, and analytical expressions are obtained which describe the main characteristics of the process.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 56–60, September, 1988.     

Plasma in open magnetic trap injected from independent UHF source

The properties of plasma injected into the open magnetic trap of uniform field from an independent UHF source have been investigated. It is established that a rather quiescent plasma with control density within the range of 2×10⁸–2×10¹² cm^–3 and temperature 2–3 eV is accumulated in the trap. It turned out that plasma lifetime in the trap is determined by a classical mechanism of particle escape at the expense of collisions, at fixed value of magnetic field in the trap it is not practically changed with the variation of neutral gas pressure and reaches the maximum value 4×10^–3 s at magnetic field strength in the trap equal 1600 Oe. Besides, the experimental data are analyzed on the basis of balance equations.     

Hydrodynamic theory of electron transport in a strong magnetic field

The mode coupling contribution to the transverse transport coefficients of a three-dimensional one-component plasma in a strong external magnetic field is calculated. For very strong fields it is found that the tagged particle diffusion rate, the thermal diffusion rate, and the coefficient of viscosity in the plane orthogonal to the field have a Bohm-like B ^–1 behavior. The mode coupling mechanism responsible for such an effect is always one that involves the finite-frequency upper hybrid modes.     

New Models for the Solution of Intermediate Regimes in Transport Theory and Radiative Transfer: Existence Theory, Positivity, Asymptotic Analysis, and Approximations

In this paper we propose, derive, and establish the mathematical foundations of new models for the solution of intermediate regimes in transport theory and radiative transfer. These new models consist of coupling the transport equations with their diffusion approximations. Our mathematical theory includes the existence theory, the positivity of the solutions, and the asymptotic analysis. We also give the rate of the asymptotic decay. In order to solve the new coupled problem we propose to use the transmission time marching algorithm introduced and studied in refs. 10, 13–15. We then study the convergence of the resulting algorithm. These studies are based in an essential way on the methods we introduced in refs. 14, 15.     

Dynamics of light-induced diffraction gratings in silicon excited by picosecond pulses

On the basis of a numerical solution of the system of continuity equations we analyze the formation and decay of light-induced diffraction gratings in silicon under excitation by picosecond pulses. The concentration of nonequilibrium carriers generated at excitation-pulse intensities I₀ 10¹⁰ W/cm² reaches values of 10¹⁹–10²⁰ cm^–3. Estimates of the relaxation time of diffraction gratings from widely used formulas are shown to be too low because of the nonlinearity of the evolution of nonequilibrium carriers. The internal electric fields are calculated. The dynamics of diffraction gratings that are nonuniform over the depth of the sample have been studied experimentally as a function of the intensity of the excitation pulses. The experimental data accord with the results of numerical calculations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 53–58, March, 1990.     

Dynamics of nonspecific adsorption of insulin to erythrocyte membranes

Molecules may arrive at targets (receptors, enzymes, etc.) localized on a membrane surface by first adsorbing onto the surface and then surface diffusing to the targets. The flux rate of molecules arriving at targets via this mechanism depends on the surface diffusion coefficient of the molecules and, in some circumstances, on the adsorption/desorption kinetics. The technique of total internal reflection with fluorescence recovery after photobleaching (TIR-FRAP) was used here to study these rate parameters of fluorescein-labeled insulin (f-insulin) interacting with erythrocyte ghosts. Ghosts were adhered to polylysine coated slides for TIR illumination. Some ghosts became flattened and unsealed on the polylysine so that both extracellular and cytoplasmic sides of the membrane were openly exposed to the solution. An aluminum thin film between the polylysine and the fused silica of a slide quenched background fluorescence from f-insulin adsorbed directly onto the polylysine. An interference fringe pattern from two intersecting and totally internally reflecting laser beams provided surface-selective excitation with a spatial variation of illumination intensity across a ghost for surface diffusion measurements. Measured characteristic values of desorption rate constants ranged from 0.043 to 270 s^–1. According to a preexisting theoretical model, the largest desorption rate constant in this range would result in some increase in the total flux rate to a perfect sink target due to capture from the surface, provided that the surface diffusion coefficient was about 10^–8 cm²/s. However, based on TIR-FRAP measurements on our system, we estimate that the surface diffusion coefficient is less than about 5×10^–10 cm²/s. The combination of novel techniques presented here may prove valuable to other workers seeking to make diffusive and chemical kinetic rate parameter measurements of biomolecules at biological cell membranes.     

Diffusion coefficient of selenium in indium antimonide

The diffusion of selenium in indium antimonide has been studied in the temperature range 400–490°C, by the method of removing layers. Two regions have been distinguished in the donor distribution profiles. The first has a low diffusion coefficient and a high surface concentration, near to the limit of solubility of selenium (8·10¹⁸ cm^–3). In the second region, a much larger diffusion coefficient and a surface concentration lower by two orders of magnitude (8·10¹⁶ cm^–3) with weak temperature dependence are found. The temperature dependences of the diffusion coefficients of the first and second regions can be described by the expressions: D=4.8·10¹³ exp(–4.1 eV/kT) cm²/sec, D₂=1.9·10¹³ exp(–3.9 eV/kT) cm²/sec.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 40–43, November, 1991.     

Mechanism controlling the mass transfer in the diffusional motion of crystalline particles in a metallic matrix

The motion of individual HfO₂ particles in a Ni-HfO₂ alloy at T=1623 K is investigated. It is established that the velocity of particle motion V depends on their radius according to the law V r^–3. The mechanism of particle motion in the given conditions is analyzed. It is shown that the mechanism controlling the mass transfer in particle motion is diffusion through the volume of the matrix.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 88–92, February, 1992.     

Experimental determination of mutual-diffusion coefficients in gases

A steady-state solution is found for the distributions of concentration, pressure, and mass-average velocity along a capillary joining two gas-filled volumes with and without an account of diffusive slip. Despite the mass-average motion, experimental data can be analyzed on the basis of the ordinary Fick's law. The experimental results are compared with equations for the mutual-diffusion coefficient given by the rigorous Chapman-Enskog kinetic theory.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 1, pp. 113–118, January, 1970.     

Silver release from nanocomposite Ag/alginate hydrogels in the presence of chloride ions: experimental results and mathematical modeling

A stepwise experimental and mathematical modeling approach was used to assess silver release from nanocomposite Ag/alginate microbeads in wet and dried forms into water and into normal saline solution chosen as a simplified model for certain biological fluids (e.g., blood plasma, wound exudates, sweat, etc). Three phenomena were connected and mathematically described: diffusion of silver nanoparticles (AgNPs) within the alginate hydrogel, AgNP oxidation/dissolution and reaction with chloride ions, and diffusion of the resultant silver-chloride species. Mathematical modeling results agreed well with the experimental data with the AgNP diffusion coefficient estimated as 1.3 × 10^?18 m² s^?1, while the first-order kinetic rate constant of AgNP oxidation/dissolution and diffusivity of silver-chloride species were shown to be inversely related. In specific, rapid rehydration and swelling of dry Ag/alginate microbeads induced fast AgNP oxidation/dissolution reaction with Cl^? and AgCl precipitation within the microbeads with the lowest diffusivity of silver-chloride species compared to wet microbeads in normal saline. The proposed mathematical model provided an insight into the phenomena related to silver release from nanocomposite Ca-alginate hydrogels relevant for use of antimicrobial devices and established, at the same time, a basis for further in-depth studies of AgNP interactions in hydrogels in the presence of chloride ions.     

Quasiparticle recombination time in superconducting tin and normal electronic density of states at the fermi surface from tunnel junction experiments

We have measured the temperature dependence of the effective quasiparticle recombination time in superconducting tin tunnel junctions by current and laser pulse excitation. The experimental times show satisfactory agreement with calculations based on the ray acoustic lifetime model of Eisenmenger et al. taking into account the film thickness dependence of the phonon reabsorption, 2-phonon volume loss processes and phonon transmission from the junction into the substrate and liquid helium. On the basis of the BCS density of thermally excited quasiparticles and simplified rate equations for quasiparticle recombination, and from the analysis of measurements of decaying excess quasiparticle concentrations we obtain a mean valueN ₀=(2.73±0.03) 10²² eV^–1 cm^–3 for the electronic density of states at the Fermi Surface in thin, evaporated tin films. This value differs less than 5% from that obtained from the experimental electronic heat-capacity coefficient of the bulk material.IBM Zürich, Research Laboratory, CH-8803, Rüschlikon, Switzerland     

Transient photocurrents in UV-irradiated polytetrafluoroethylene coronoelectrets

It is experimentally found that UV irradiation of 10-m polytetrafluoroethylene films electrified in a negative corona discharge produces a transient current which is unipolar and whose peak value decreases in successive exposures. A model is considered on the basis of spatial impurity-center photoionization and the resultant positive-carrier motion, excluding recapture and recombination, in the strong internal field generated by trapped negative charges. Correlation of the experimental and calculated photocurrent kinetics yield values for the hole mobility (8.9×10^–15 m²·V^–1·sec^–1) and impurity-center concentration (1.5×10¹⁸ m^–3).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 26–29, June, 1990.     

Mixing of toponium and Z° boson in elastic e+ − annihilation

If toponium with a mass close to the mass of a Z meson exists, it could be studied on the basis of the interference pattern which would be produced in the differential cross section for elastic e⁺e^– annihilation with unpolarized initial beams. The energy and angular dependence of the quantity which determines the relative contribution of vector toponium to the differential cross section for the process e⁺e^– e⁺e^– has been studied.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika,No. 10, pp. 38–42, October, 1988.     

Volume and grain boundary diffusion of implanted 113Sn in aluminium

Volume and grain boundary diffusion of ¹¹³Sn in aluminium was investigated with the radiotracer method. The implantation technique was used for tracer deposition to avoid problems of tracer hold-up caused by the oxide layer always present on aluminium. The diffusion penetration was chosen large enough to permit serial sectioning of samples with the aid of a microtome.The temperature dependence of the volume diffusivity was determined as D(T)=4.54×10^–5×exp[–(114.5±1.2)kJmol^–1/RT] m ² s ^–1. This confirms previous measurements from our group which already showed that Sn is the fastest foreign metal diffusor so far investigated in aluminium.Grain boundary diffusion of ¹¹³Sn in Al polycrystals was measured in the type-B kinetic regime. The grain boundary diffusion product P=sD _gb (s=segregation factor, =grain boundary width, D _gb=grain boundary diffusivity) was found to be strongly affected by the impurity content of aluminium. For Al polycrystals of 99.9992% nominal purity we obtained P _5N(T)=1.08×10^–8exp [–(96.9±7.5) kJ mol^–1/RT] m³ s^–1 and for less pure Al polycrystals of 99.99% nominal purity P _4N(T)=3.0×10^–10 exp [–(90.1±4.2) kJ mol^–1/RT] m³ s^–1 was determined. The grain boundary diffusion product in the purer material is more than one order of magnitude higher than in the less pure material. Very likely this is an effect of co-segregation of non-diffusant impurities into the grain boundaries.     

Green's function for the Dirac equation with nonsingular central potential and complex energy. Estimation algorithm

Calculation of the electron radial Green's function leads to solution of a system of ordinary differential equations for three functions: F, G, which represent the regular solution of the Dirac equation for r 0, and W^– (the antiWronskian) —a function regular everywhere: W^– = 1 for r = 0; W^– 1/r as r . An algorithm is formulated for calculating boundary values of W^– as r 0 and for estimation purposes at asymptotically large values of r.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 34–42, August, 1990.     

Experimental and Real Coordinates in Space-Time Transformations

The experimental (apparent) space-time transformations connect coordinates altered by length contraction and clock retardation. When clocks are synchronized by means of light signals (Einstein–Poincaré procedure) or by slow clock transport, the experimental space-time. transformations assume the mathematical form of the Extended space-time transformations.⁽⁴⁾ These reduce to the Lorentz–Poincaré transformations when one of the frames they connect is the fundamental inertial frame. If the synchronization procedure were perfect, the experimental space-time transformations would assume the form of Selleris inertial transformations.⁽⁵⁾ The real space-time transformations are those which are disclosed when the systematic measurement distortions are corrected.