Influence of a variable magnetic field on the stability of the magnetic suspension of high-T c superconductors

The resonant oscillation of superconductors by a variable magnetic field during hard levitation and the collapse of levitation are investigated. The critical amplitude and the frequency of the variable field are calculated. Zh. Tekh. Fiz. 67, 95–96 (December 1997)     

Determination of the concentration profile of interfaces in multilayered nanostructures according to the angular dependence of X-ray photoelectron spectra: A new approach

The possibility of determining the concentration profile of interfaces in multilayered nanoheterostructures according to the data of the angular dependence of X-ray photoelectron spectra was shown. To solve this ill-posed inverse problem, we used Tikhonov’s regularization method with iterative refinement. To determine the optimum parameter of regularization, we used the L curve technique. The programs used for this study allowed high accuracy of calculations. All this made it possible to obtain information about the distribution of atoms of a definite sort with a resolution of 0.1–0.15 nm in depth. The results of numerical simulation of XPS spectra are given for a three-layered Cr/Fe structure. Solving the inverse problem for the initial data distorted by the statistical noise afforded a concentration distribution over depth for Cr and Fe atoms. The stability of the solution against experimental errors was determined.     

Study on a Bridge-Type Stripline Parametric Scatterer

Radiophysics and Quantum Electronics - We propose and have implemented a design of a bridge-type stripline parameteric scatterer. It is a system of four parametric oscillators connected according...     

Mechanisms of surface processes in silicon etching

A unified view on the mechanism allowing one to explain the experimental features governing spontaneous silicon etching by atomic fluorine is presented. Analysis of the phenomenological equation of adsorption shows a significant difference between etching mechanisms at high and low heat of adsorption on the surface being etched. As follows from the parameter estimates, one or another case can be realized under different experimental conditions. At steady-state the etching is argued to be determined only by the processes taking place on the SiF. film surface. To describe the process, it is necessary to understand the mechanism of overcoming the surface barrier for fluorine penetration into the film. At low heat of fluorine adsorption the barrier is overcome by thermal activation. In the opposite case the etching mechanism includes electron tunneling from silicon to adatoms and creation of a surface electric field. The field lowers the high energetic barrier for fluorine penetration. Based on the kinetic equations describing the electronic and atomic processes on the surface, the equation of the field strength is obtained. This equation is analyzed in different limit cases. The observed features are shown to be reproduced at some conditions on the parameters. Definite predictions on the temperature dependence of the etch rate are made.     

Striking anomalies in the shape of Mössbauer spectra measured near “magnetic” Bragg reflection from [Fe/Cr] multilayer

The present work reports the observation of a peculiar asymmetry of the Mössbauer spectra of reflectivity from a periodic [⁵⁷Fe(8Å)/Cr(10.5Å)]₃₀ multilayer measured on both slopes of the half-order “magnetic” Bragg peak. The performed analysis and model calculations confirm the responsibility of the refraction effect for the observed features.     

The determination of the true profile of XPS line by regularization method: I. Mathematical algorithm and numerical simulations

The resolution of XPS spectra is limited mainly by instrumental parameters like the spectral line width of exciting X-ray source and the finite energy resolution of the electron analyzer. A new algorithm of an inverse ill-posed problem has been proposed in which low resolution experimental XPS data can be enhanced by removing the instrumental functions. The regularization method with a special fast iteration algorithm is applied for determining the true profile line of a complex chemical compound if we know excitation and instrumental functions. This paper is structured as follows: (I) a mathematical algorithm is described and numerical simulation results are presented. (II) These algorithms have been applied to the poorly resolved C 1s spectrum of a poly-methyl methacrylate (PMMA) film studied by the conventional technique with monochromatic and polychromatic radiation. The resulting enhancement allows previously unresolved structure to be observed without any assumptions concerning number, position, shape of peaks and their ratio.     

Correcting an experimental absorption spectrum for the core level width

The problem of correcting EXAFS spectra by the core level width is discussed. A method of correcting experimental EXAFS spectra is developed. An iteration algorithm for solving the integral equation is proposed. This method has a number of advantages over other methods, namely, high stability against statistical error and fast convergence. Model numerical calculations are performed. An example is the EXAFS spectrum of polycrystalline Pd for which the broadening effect is significant. Translated fromZhumal Struktumoi Khimii, Vol. 39, No. 6, pp. 1018–1024, November–December, 1998.     

New possibilities of the EXAFS spectroscopy in study of the local atomic structure of multilayer nanoheterostructures

New possibilities of studying the local atomic structure of multilayer nanoheterostructures by EXAFS spectroscopy have been considered. It is shown that this method makes it possible to determine the average partial interatomic distances for overlapping coordination spheres with a small error (～0.01 Å). As an example, the experimental results for a sample of a (FeNi)/V multilayer nanoheterostructure.     

Combining X-ray scattering and exafs experiments for studying amorphous alloys of 3d transition metals with zirconium

The atomic structure of the amorphous alloys of several transition metals (Fe, Co, Ni, and Cu) with zirconium is studied in terms of partial paired correlation functions. The short-range order parameters, namely, the shortest interatomic distances, coordination numbers, and the form of distribution functions, are compared and a correlation between the atomic structure and the interaction between atoms of different sorts is established. The study offers the possibility to model the spatial distribution of atoms and the physical properties of the analyzed alloys and predict the properties of new systems. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 6, pp. 1025–1030, November–December, 1998.