Coatings by refractory metal carbides: Deposition from molten salts,properties, application

High-temperature electrochemical synthesis and currentless transfer in molten salts were used to obtain coatings constituted by carbides of refractory metals (Mo₂C, Cr₇C₃, NbC, and TaC). It was found that the Mo₂C/Mo composite synthesized from a chloride-carbonate-molybdate melt has the highest catalytic activity. It was shown that the Mo₂C catalytic coating preserves its properties for at least 5000 h of tests. The protective properties of refractory metal carbides of composition Cr₇C₃, NbC, and TaC significantly improve the corrosion resistance of steel articles in concentrated solutions and raise their wear resistance by an order of magnitude.     

Self-consistent model of nanowire growth and crystal structure with regard to the adatom diffusion

A self-consistent model of growth and structure of semiconductor nanowires is proposed. The crystal phase of group III–V semiconductor nanowires is studied. The critical radius of the transition from the hexagonal wurtzite (WZ) structure to the cubic structure of zinc blende (ZB) type is calculated as a function of parameters of the system of materials and the gaseous medium supersaturation. The model presented here is applicable to both gas-phase and molecular beam epitaxies and allows one to calculate the probability of formation of the WZ and ZB phases under various deposition conditions.     

Nonstationary photovoltage induced in tin disulfide crystals under strong surface excitation

The specific features of nonstationary photovoltage excitation in molecular crystals of tin disulfide are investigated. A substantial change in the dependence of the photocurrent amplitude on the spatial frequency of the interference pattern is revealed. The observed behavior is explained in terms of the model of a photoconductor with different-type charge carriers of the same sign.     

The magnetic field and energy of an Abrikosov vortex in an anisotropic London superconductor

The behavior of a straight Abrikosov vortex in an anisotropic uniaxial London superconductor is studied. Analytical expressions are derived that approximately describe the magnetic field in three regions: the asymptotic region, where the distance r from the vortex line is greater than λΓ (λ is the London length and Γ is the anisotropy constant), the intermediate region λ<r<λΓ, and the region r<λ. It is found that in the intermediate region with high anisotropy the component of the magnetic field along the vortex line changes sign for a certain interval of angles between the vortex line and the anisotropy axis. Because of this the interaction of parallel vortices whose plane is parallel to the anisotropy axis has a minimum and a maximum. This means that numerous metastable vortex lattices can exist. Additional terms in the vortex self-energy are obtained, and although they are smaller than the leading logarithmic term, they display a different dependence on the angle between the vortex line and the anisotropy axis. Zh. éksp. Teor. Fiz. 111, 954–963 (March 1997)     

Electronic structure and spectral characteristics of Bi-Sr-Ca-Cu-O films

The electronic structure of high-temperature superconducting films of Bi-Sr-Ca-Cu-O is determined using the linearized augmented plane wave method. Total and local partial densities of states are calculated for each film using the results of band structure calculations. Theoretical OK_α and CuL_α X-ray emission spectra are found. The dependence of the electronic structure and spectra on the number of CuO₂ layers in the unit cell is discussed. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 6, pp. 1067–1075, November–December, 1998.     

Quasi-classical analytical approximation of theS-matrix for the three-particle collinear rearrangement reaction

In the framework of the quasi-classical method of the Fock-Leontovich parabolic equation, the collinear problem of the three-particle rearrangement reaction is reduced to the quantum problem of a one-dimensional harmonic oscillator with a variable frequency in an external force field. This allows one to express the S-matrix elements responsible for the rearrangement channel via the known analytical functions of the oscillator model, using the parameters of the potential surface of a linear configuration of three particles.Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 107, No. 2, pp. 238–250, May, 1996.Translated by T. F. Drozdova.     

Relaxation of anharmonic molecules

The inclusion of anharmonic effects is important in vibrational population inversions in CO-lasers [1, 2], in relaxation processes in jets [3], in thermal dissociation [1], in the kinetics of chemical reactions with high thresholds [4], etc. Usually these effects are studied by including anharmonic corrections to the kinetic constants in the discrete model of single-quantum transitions or in the diffusion approximation [1, 2]. In [5] a method was given of solving the relaxation equations fro arbitrary forms of the rate constants and the spectrum of the molecule. The method is valid when the ratio of the population densities of neighboring levels varies smoothly with quantum number. It was shown in [5] that this approximation can be used to construct analytical solutions for a wide class of problems. In the present paper the method of [5] is extended to the case of equations with variable coefficients. The properties of the solutions for VT-relaxation of anharmonic molecules are analyzed, and the inclusion of sources is considered. A simple method of taking into account multiple-quantum transitions is given, as well as an extension of the method to an arbitrary mixture of gases. The population densities are calculated and the possibility of using our solutions in relaxation gas dynamics is discussed.Translated from Zhurnal Prikladnoi Mekhaniki Tekhnicheskoi Fiziki, No. 3, pp. 22–31, May–June, 1986.     

Anisotropy of electronic wave functions in self-assembled InAs dots embedded in the center of a GaAs quantum well studied by magnetotunneling spectroscopy

We present an experimental study of electron wave functions in InAs/GaAs self-assembled quantum dots by magnetotunneling spectroscopy. The electronic wave functions have a biaxial symmetry in the growth plane, with axes corresponding to the main crystallographic directions in the growth plane. Moreover, we observed the in-plane anisotropy of the subbands of the quantum well.