Tshevchenko National University Of Kyiv

Kiev, Ukraine

Tshevchenko National University Of Kyiv

Kiev, Ukraine
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Milovanov Y.S.,Tshevchenko National University Of Kyiv | Gavrilchenko I.V.,Tshevchenko National University Of Kyiv | Kondratenko S.V.,Tshevchenko National University Of Kyiv | Oksanich A.P.,Kremenchuk National University | And 2 more authors.
Functional Materials | Year: 2017

Porous GaAs was formed electrochemically on n-type GaAs in a HF:C2H5OH (1:3) electrolyte. The surface morphology of porous GaAs has been studied using atomic force microscopy (AFM). The hodographs of the total impedance and the adsorption influence of ethanol and acetone vapor on the charge transfer were examined. © 2017. STC "Institute for Single Crystals". All rights reserved.

Prokopenko O.V.,Tshevchenko National University Of Kyiv | Tiberkevich V.S.,Oakland University | Slavin A.N.,Oakland University
Functional Materials | Year: 2014

The analytical theory of magnetization dynamics in a dual-free-layer spin-torque nano-oscillator (DFL STNO) operating in the absence of a bias magnetic field is developed. The theory is based on a system of simplified dynamic equations written in collective variables and yields an analytic expression for the upper dc current density threshold of stable magnetization dynamics (generation) in the DFL STNO. This threshold is caused by a dipolar coupling between the free layers and can be controlled by choosing an appropriate geometry of the DFL STNO structure. © 2014-STC "Institute for Single Crystals".

Lozovski V.,Tshevchenko National University Of Kyiv | Motornyi O.,Tshevchenko National University Of Kyiv
2015 IEEE 35th International Conference on Electronics and Nanotechnology, ELNANO 2015 - Conference Proceedings | Year: 2015

The theoretical aspects of visualization of nano-objects by scattering of surface plasmon-polariton are discussed in the frame of local-field approach. It was shown that the image intensity measured by the optical detector depends on the distance between nano-object and surface and their interaction is resonant. Besides, it was shown that the main feature of the used approach is taken into account the inhomogeneity of the local field at the nanoparticle. In part, it was obtained that position of maximum intensity depends linear on particle radius. The results of calculations were compared with experimental data obtained by other scientific teams. © 2015 IEEE.

Buchenko V.V.,Tshevchenko National University Of Kyiv | Goloborodko A.A.,Tshevchenko National University Of Kyiv
Functional Materials | Year: 2016

The present paper dedicated to experimental investigations of optical properties of Bi/Si(001) interfaces and Bi nanolines in a wide spectral range (1÷4eV). The experimental study of optical absorption spectrum showed the widening of the optical band gap of Bi/Si(001) interfaces with increasing the bismuth coverage, whereas after nanolines formation the width of the optical band gap decreases. Features of the experimentally obtained reflectance anisotropy spectra and surface differential reflectance spectra concerned with changing of the silicon surface reconstruction from 2x1 to 1x1 with the increasing of the bismuth covering degree from 0.5 ML to 1 ML. The experimental study of reflectance anisotropy spectra and surface differential reflectance spectra of Bi nanolines shows that the bismuth atoms are still present on the surface of the substrate in small amount, but the optical properties of such structures are determined by Si dimers. © 2016 - STC "Institute for Single Crystals".

Strutynska N.Y.,Tshevchenko National University Of Kyiv | Bondarenko M.A.,Tshevchenko National University Of Kyiv | Zatovsky I.V.,Tshevchenko National University Of Kyiv | Babaryk A.A.,Tshevchenko National University Of Kyiv | Slobodyanyk N.S.,Tshevchenko National University Of Kyiv
Functional Materials | Year: 2015

Peculiarities of phase formation in the self-flux of systems MI2O-P2O5-TiO2-MIIO (MI - Rb, Rb/K, MII - Cu, Zn) were investigated at different molar ratios MIP = 0.5-1.3 and fixed values Ti/P = 0.3, Ti/MII = 1.0 in the temperature range of 1000-650°C. Influence of the nature of alkali metal on interaction in multicomponent phosphate melts at molar ratios (Rb+K)/P = 1.0, Ti/P = 0.3, Ti/MII=1.0 was found. Thus, the presence of potassium in the melts promotes the formation of langbeinite-related complex phosphates at the investigated ratios of components. The obtained phosphates were investigated by X-ray powder diffraction, infrared spectroscopy and optical microscopy. © 2015 - STC "Institute for Single Crystals".

Akimenko V.V.,Tshevchenko National University Of Kyiv
Mathematics and Computers in Simulation | Year: 2015

This paper is devoted to the study of evolutionary dynamics of monocyclic age-structured population including effect of nonlinear mortality (population growth feedback) and proliferation. The total population is considered as partitioned by fixing age into two subpopulations. Individuals of first population are born, mature, die and can at the final fixed age give birth for some new individuals (with null age). Individuals of the second subpopulation are older than those of the first one. They can mature, die and do not have possibility to proliferate. This model was considered as a system of two initial-boundary value problems for nonlinear transport equations with non-local boundary conditions. We obtained explicit travelling wave solution provided the model parameters (coefficients of equations and initial values) satisfy the restrictions that guarantee continuity and smoothness of solution. Explicit form of solution allowed us to perform numerical experiments with high accuracy using the set of parameterized algebraic functions which do not depend from the time. In all performed experiments solutions are attracted to some stationary functions for a long time period (asymptotically stable states of system). We indicated and studied three different regimes of population dynamics. The first is quasi-equilibrium regime, when the maximum value of population density by age, as a function of time, is attracted to the point from the neighbourhood of initial value. This is a result of balance between effects of proliferation and nonlinear mortality (like behaviour of microorganism population in the cases of asymptomatic or healthy carriers). The second and third regimes are characterized by increasing (decreasing) maximum by age values of population density with following attracting to values higher (lower) than initial one. We studied also the impact of parameters of nonlinear death rate on the tremendous growth of population density followed by transition to asymptotically stable states (like infection generalization process in living organisms). © 2015 International Association for Mathematics and Computers in Simulation (IMACS).

Rozouvan T.,Tshevchenko National University Of Kyiv | Yurgelevich I.,Tshevchenko National University Of Kyiv | Rozouvan S.,Tshevchenko National University Of Kyiv | Poperenko L.,Tshevchenko National University Of Kyiv
Functional Materials | Year: 2014

Surface structures of polycrystalline and monocrystalline samples of chromium were investigated using the following techniques: magnetic force microscopy, scanning tunneling microscopy, and spectral ellipsometric method. Presence of magnetic nanostructure on the surface of polycrystalline chromium has been explained in terms of spin orientation of the atoms. Also we carried out numerical quantum mechanical calculations of chromium supercell and analyzed the results using experimentally obtained curves of the optical conductivity for chromium single crystal. © 2014 - STC "Institute for Single Crystals".

Zharkova V.V.,Northumbria University | Siversky T.,Tshevchenko National University Of Kyiv
Journal of Physics: Conference Series | Year: 2015

Acceleration of protons and electrons in a reconnecting current sheet (RCS) is investigated with the test particle and particle-in-cell (PIC) approaches in a 3D magnetic topology. PIC simulations confirm a spatial separation of electrons and protons with respect to the midplane depending on the guiding field. Simulation reveals that the separation occurs in magnetic topologies with strong guiding fields and lasts as long as the particles are kept dragged into a current sheet. This separation produces a polarisation electric field induced by the plasma feedback to a presence of accelerated particles, which shape can change from symmetric towards the midplane (for weak guiding field) to fully asymmetric (for strong guiding field). Particles are found accelerated at a midplane of any current sheets present in the heliosphere to the energies up to hundred keV for electrons and hundred MeV for protons. The maximum energy gained by particles during their motion inside the current sheet is defined by its magnetic field topology (the ratio of magnetic field components), the side and location from the X-nullpoint, where the particles enter a current sheet. In strong magnetic fields of the solar corona with weaker guiding fields, electrons are found circulating about the midplane to large distances where proton are getting accelerated, creating about the current sheet midplane clouds of high energy electrons, which can be the source of hard X-ray emission in the coronal sources of flares. These electrons are ejected into the same footpoint as protons after the latter reach the energy sufficicent to break from a current sheet. In a weaker magnetic field of the heliosphere the bounced electrons with lower energies cannot reach the midplane turning instead at some distance D before the current sheet midplane by 180 degrees from their initial motion. Also the beams of accelerated transit and bounced particles are found to generate turbulent electric fields in a form of Langmuir waves (electrons) or ion-acoustic waves (protons). © Published under licence by IOP Publishing Ltd.

Suprun A.D.,Tshevchenko National University Of Kyiv | Shmeleva L.V.,Tshevchenko National University Of Kyiv
Functional Materials | Year: 2012

The general dynamical properties of free quasi-particles are analyzed. Analyzed also the conditions under which the description of the dynamic properties of the quasi-particles is almost identical with those of real relativistic particles. The problem of the relation of quantum and classical methods of describing the quasi-particles in the case of the excited states of crystals is considered. Basic principles of construction of dynamic properties of classic type for quasi-particles at excitation of matter with the structure of solids (crystals) are analyzed. The results of analysis were demonstrated on the example of electronic excitations of crystals in the simplest case, when other effects are neglected (phonons, the response to excitation of the lattice, defects, high density of excitations, which requires the account of interactions between them, and so forth). It was shown that such excitations are described in three ways simultaneously. These descriptions make it possible to interpret the experimental data in terms of the usual relativistic dynamics, if the considered system allows the use of the considered approximations (plane wave in a phase, nearest neighbors and cubic grate). © 2012 - STC Institute for Single Crystals.

Kosach V.V.,Tshevchenko National University Of Kyiv | Pivovarenko V.G.,Tshevchenko National University Of Kyiv | Yashchuk V.M.,Tshevchenko National University Of Kyiv
Functional Materials | Year: 2016

The spectral peculiarities of polymer/dye solid mixtures on the base of PEPCa polymer (polyepoxypropylcarbazole) as matrix and DFOM (3,7-dihydroxy-2,8-diphenyl-4H,6H-pyrano[3,2-g] chromene-4,6-diones) as emitter were investigated. Peculiarities intramolecular proton transference after the excitation of molecule, incident to this material, allows one to create emitting layer with emission spectrum close to white light and using only one luminophore. Spectral behavior of investigated compounds proves the presence of excitation energy transfer from the PEPCa matrix to the DFOM molecules, which is necessary for effective use of the excitation energy and forming luminescence curve needed. Luminescence of the investigated films demonstrates color characteristics CRI 54 and CIE (0.33, 0.42) which gives a possibility to consider such systems as promising in the context of developing White OLED emitters. © 2016 - STC "Institute for Single Crystals".

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