Influence of UV Radiation on the Processes Proceeding on the Anthracene Single Crystal Surface

Russian Physics Journal - In this study, the influence of the annealing conditions on the formation of macrosteps on the anthracene single crystal surface is demonstrated. Under normal conditions...     

Investigation of nonstationary models of laser pulse propagation through a homogeneous scattering layer

Using three nonstationary models of radiation transfer in two versions (diffusion-based and axial), the absorption and scattering coefficients of homogeneous scattering media are found from experimental temporal distributions of an ultrashort laser pulse transmitted through the scattering layer of different thickness. These optical characteristics are found to be dependent on the scattering layer thickness, which contradicts physical considerations. The reason for the discovered effect is related to incomplete taking into account of the properties of the scattering indicatrix in the used approximate models. The validity of this interpretation is supported by a Monte Carlo simulation, which yielded similar dependences. Recommendations on the correct use of the approximate radiation transfer models are given.     

Synthesis of a periodic SiC/C nanostructure

Highly porous periodic structures consisting of a three-dimensional replica of pores in the initial opal lattice have been synthesized by high-temperature thermochemical treatment of opal matrices filled with carbon compounds, followed by dissolution of silicon dioxide. It has been shown that the main phases of the composite are carbon and silicon carbide. Based on the X-ray diffraction, Raman, and IR spectroscopy data, it has been assumed that the composite contains fragments of hexagonal diamond. The photoluminescence and optical reflection spectra of the composites have been measured.     

Flame structure of HMX/GAP propellant at high pressure

The chemical and thermal structure of a HMX/GAP propellant flame was investigated at a pressure of 0.5 MPa using molecular beam mass spectrometry and a microthermocouple technique. The pressure dependence of the burning rate was measured in the pressure range of 0.5–2 MPa. The mass spectrometric probing technique developed for flames of energetic materials was updated to study the chemical structure of HMX/GAP flames at high pressures. Eleven species, including HMX vapor, were identified, and their concentrations were measured in a zone adjacent to the burning surface at pressures of 0.5 and 1 MPa. Temperature profiles in the propellant combustion wave were measured at pressures of 0.5 and 1 MPa. Species concentration profiles were measured at 0.5 MPa. Two main zones of chemical reactions in the flame were found. The data obtained can be used to develop and validate combustion models for HMX/GAP propellants.     

Study of the electrical and optical properties of silicon containing oxygen precipitates

The properties of n-type silicon with oxygen precipitates introduced by three-stage annealing were studied by the electron beam induced current (EBIC) method, deep-level transient spectroscopy (DLTS), and photoluminescence (PL). The presence of extended defects with concentration of ≤10⁹ cm^?3 is revealed by the EBIC method. The concentration of electrically active defects formed in silicon due to oxygen precipitation is estimated from the EBIC contrast and is compared to that obtained from the DLTS data. Comparing the spectra of samples with oxygen precipitates with those of plastically deformed crystals, we can assume that the DLTS and PL spectra of silicon with oxygen precipitates are mainly determined by dislocations.     

On the algorithm of the solution of the signorini problem

An algorithm is proposed for solving the Signorini problem /1/ in the formulation of a unilateral variational problem for the boundary functional in the zone of possible contact /2/. The algorithm is based on a dual formulation of Lagrange maximin problems for whose solution a decomposition approach is used in the following sense: a Ritz process in the basis functions that satisfy the linear constraint of the problem, the differential equation in the domain, is used in solving the minimum problem (with fixed Lagrange multipliers); the maximum problem is solved by the method of descent (a generalization of the Frank-Wolf method) under convexity constraints on the Lagrange multipliers. The algorithm constructed can be conisidered as a modification of the well-known algorithm to find the Udzawa-Arrow-Hurwitz saddle points /3, 4/. The convergence of the algorithm is investigated. A numerical analysis of the algorithm is performed in the example of a classical contact problem about the insertion of a stamp in an elastic half-plane under approximation of the contact boundary by isoparametric boundary elements. The comparative efficiency of the algorithm is associated with the reduction in the dimensionality of the boundary value problem being solved and the possibility of utilizing the calculation apparatus of the method of boundary elements to realize the solution.     

The Influence of Macrocyclic Tetraamine Immobilization in Langmuir Monolayers on Complex Formation Selectivity

Selective complex formation in Langmuir dicetyl cyclene monolayers on the surface of aqueous solutions of Cu(II), Ni(II), and Zn(II) salts and their mixtures was studied. The effect of selectivity “inversion” of diphilic cyclene immobilized in monolayers on the surface of solutions of a mixture of copper(II) and nickel(II) salts was observed; the inversion was induced by a change in subphase pH. An analysis of the isotherms of monolayer compression and X-ray fluorescence spectra of the corresponding Langmuir-Blodgett films showed that subphase acidification caused a gradual transition from the selective formation of copper-containing macrocyclic complexes to selective complex formation between the ligand and nickel ions. The effect observed was not characteristic of complex formation with similar unsubstituted tetraamines in bulk solution. The phenomenon was interpreted from the point of view of specific conformational transitions of the diphilic macroring in the two-dimensional system organized at the interphase boundary.     

Surface spin-polarized currents generated in topological insulators by circularly polarized synchrotron radiation and their photoelectron spectroscopy indication

A new method for generating spin-polarized currents in topological insulators has been proposed and investigated. The method is associated with the spin-dependent asymmetry of the generation of holes at the Fermi level for branches of topological surface states with the opposite spin orientation under the circularly polarized synchrotron radiation. The result of the generation of holes is the formation of compensating spin-polarized currents, the value of which is determined by the concentration of the generated holes and depends on the specific features of the electronic and spin structures of the system. The indicator of the formed spin-polarized current can be a shift of the Fermi edge in the photoelectron spectra upon photoexcitation by synchrotron radiation with the opposite circular polarization. The topological insulators with different stoichiometric compositions (Bi_1.5Sb_0.5Te_1.8Se_1.2 and PbBi₂Se₂Te₂) have been investigated. It has been found that there is a correlation in the shifts and generated spin-polarized currents with the specific features of the electronic spin structure. Investigations of the graphene/Pt(111) system have demonstrated the possibility of using this method for other systems with a spin-polarized electronic structure.