NASU Institute of Physics

Kiev, Ukraine

NASU Institute of Physics

Kiev, Ukraine

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Radchenko T.M.,Linköping University | Radchenko T.M.,NASU Institute of Physics | Shylau A.A.,Linköping University | Zozoulenko I.V.,Linköping University
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Numerical calculations of the conductivity of graphene sheets with random and correlated distributions of disorders have been performed using the time-dependent real-space Kubo formalism. The disorder was modeled by the long-range Gaussian potential describing screened charged impurities and by the short-range potential describing neutral adatoms both in the weak and strong scattering regimes. Our central result is that correlation in the spatial distribution for the strong short-range scatterers and for the long-range Gaussian potential do not lead to any enhancement of the conductivity in comparison to the uncorrelated case. Our results strongly indicate that the temperature enhancement of the conductivity reported in the recent study and attributed to the effect of dopant correlations was most likely caused by other factors not related to the correlations in the scattering potential. © 2012 American Physical Society.


Filippov A.E.,NASU Institute of Physics | Popov V.L.,TU Berlin | Urbakh M.,Tel Aviv University
Physical Review Letters | Year: 2011

We propose a model for a description of formation of quasiperiodic nanoscale patterns induced by scratching a surface with an atomic force microscope tip. The simulations demonstrate that the interplay between the developing surface corrugation and the frictional stress produced by the moving tip plays a decisive role in the formation of the regular ripples. Our model reveals the size and shape of the tip as the main factors that determine periodicity and amplitudes of the patterns, and it allows experimental observations to be explained. It is shown that the wear at the nanoscale cannot be explained by conventional macroscopic wear theories. © 2011 American Physical Society.


Pohrt R.,TU Berlin | Popov V.L.,TU Berlin | Filippov A.E.,NASU Institute of Physics
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

It was shown earlier that some classes of three-dimensional contact problems can be mapped onto one-dimensional systems without loss of essential macroscopic information, thus allowing for immense acceleration of numerical simulations. The validity of this method of reduction of dimensionality has been strictly proven for contact of any axisymmetric bodies, both with and without adhesion. In, it was shown that this method is valid "with empirical accuracy" for the simulation of contacts between randomly rough surfaces. In the present paper, we compare exact calculations of contact stiffness between elastic bodies with fractal rough surfaces (carried out by means of the boundary element method) with results of the corresponding one-dimensional model. Both calculations independently predict the contact stiffness as a function of the applied normal force to be a power law, with the exponent varying from 0.50 to 0.85, depending on the fractal dimension. The results strongly support the application of the method of reduction of dimensionality to a general class of randomly rough surfaces. The mapping onto a one-dimensional system drastically decreases the computation time. © 2012 American Physical Society.


Filippov A.E.,NASU Institute of Physics | Vanossi A.,International School for Advanced Studies | Vanossi A.,University of Modena and Reggio Emilia | Urbakh M.,Tel Aviv University
Physical Review Letters | Year: 2010

Wearless friction force experiments have recently demonstrated that tribological response in quasicrystals could be related to the exotic atomic structure of the bulk material. Here, by numerical simulations, we address the origin of the experimentally observed friction anisotropy on a twofold decagonal quasicrystal surface. We predict the distinct stick-slip patterns in the lateral force along the periodic and quasiperiodic directions, specifically exploring the temperature dependence that rules the transitions between single and multiple-slip regimes of motion. © 2010 The American Physical Society.


De Wijn A.S.,University of Stockholm | Fasolino A.,Radboud University Nijmegen | Filippov A.E.,NASU Institute of Physics | Urbakh M.,Tel Aviv University
Physical Review Letters | Year: 2014

We propose a theoretical model of friction under electrochemical conditions focusing on the interaction of a force microscope tip with adsorbed polar molecules whose orientation depends on the applied electric field. We demonstrate that the dependence of friction force on the electric field is determined by the interplay of two channels of energy dissipation: (i) the rotation of dipoles and (ii) slips of the tip over potential barriers. We suggest a promising strategy to achieve a strong dependence of nanoscopic friction on the external field based on the competition between long-range electrostatic interactions and short-range chemical interactions between tip and adsorbed polar molecules. © 2014 American Physical Society.


Velichko E.A.,NASU Institute of Physics | Nosich A.I.,NASU Institute of Physics
Optics Letters | Year: 2013

We study the scattering and absorption of an H-polarized plane electromagnetic wave by a circular silver nanotube in the visible range of wavelengths using the separation of variables. The computed spectra of the extinction cross section display several hybrid localized surface-plasmon resonances of the dipole and multipole type. Analytical equations are derived for their resonance wavelengths. Bulk refractive-index sensitivities of nanotube-based sensors are determined, showing higher values for multipole resonances. © 2013 Optical Society of America.


Shapoval O.V.,NASU Institute of Physics | Nosich A.I.,NASU Institute of Physics
AIP Advances | Year: 2013

We study numerically the optical properties of the periodic in one dimension flat gratings made of multiple thin silver nanostrips suspended in free space. Unlike other publications, we consider the gratings that are finite however made of many strips that are well thinner than the wavelength. Our analysis is based on the combined use of two techniques earlier verified by us in the scattering by a single thin strip of conventional dielectric: the generalized (effective) boundary conditions (GBCs) imposed on the strip median lines and the Nystrom-type discretization of the associated singular and hyper-singular integral equations (IEs). The first point means that in the case of the metal strip thickness being only a small fraction of the free-space wavelength (typically 5 nm to 50 nm versus 300 nm to 1 μm) we can neglect the internal field and consider only the field limit values. In its turn, this enables reduction of the integration contour in the associated IEs to the strip median lines. This brings significant simplification of the scattering analysis while preserving a reasonably adequate modeling. The second point guarantees fast convergence and controlled accuracy of computations that enables us to compute the gratings consisting of hundreds of thin strips, with total size in hundreds of wavelengths. Thanks to this, in the H-polarization case we demonstrate the build-up of sharp grating resonances (a.k.a. as collective or lattice resonances) in the scattering and absorption cross-sections of sparse multi-strip gratings, in addition to better known localized surface-plasmon resonances on each strip. The grating modes, which are responsible for these resonances, have characteristic near-field patterns that are distinctively different from the plasmons as can be seen if the strip number gets larger. In the E-polarization case, no such resonances are detectable however the build-up of Rayleigh anomalies is observed, accompanied by the reduced scattering and absorption. © 2013 © 2013 Author(s).


Smotrova E.I.,NASU Institute of Physics | Nosich A.I.,NASU Institute of Physics
Optics Letters | Year: 2013

The lasing spectra and thresholds of a selectively pumped photonic molecule composed of two microdisks is investigated using effective index approximation and full-wave 2-D electromagnetic equations. The lasing eigenvalue problem formulation is used to find modal frequencies and threshold values of material gain. The influence of the optical coupling between active and passive microdisks on the lasing eigenvalues and directionalities of emission is studied. It is shown that for strong coupling the effect of making one of the resonators passive leads to the doubling of the threshold. © 2013 Optical Society of America.


Nosich A.I.,NASU Institute of Physics
Radio Science | Year: 2016

We discuss the advantages of the conversion of electromagnetic field problems to the Fredholm second-kind integral equations (analytical regularization) and Fredholm second-kind infinite-matrix equations (analytical preconditioning). Special attention is paid to specific features of the characterization of metals and dielectrics in the optical range and their effect on the problem formulation and on the methods applicable to the mentioned conversion. ©2016. American Geophysical Union. All Rights Reserved.


Grant
Agency: European Commission | Branch: FP7 | Program: CP | Phase: ICT-2007.8.0 | Award Amount: 2.29M | Year: 2009

New magneto-transport phenomena have been discovered in magnetic multilayers and are now being optimized for industrial applications, extending the conventional electronics with new functionality. However, most of the current research on magnetic multilayer materials and its device applications rely on conventional equilibrium electron transport. The full potential of nano-structuring, which leads to a broad spectrum of novel non-equilibrium transport phenomena, is therefore not realized. In this research project we will focus on practically unexplored functional principles that can be implemented in nanostructures produced by state-of-the-art lithography and surface manipulation techniques. Our main idea is to use electrically controlled spin currents in highly non-equilibrium regimes with respect to energy and temperature; hence spin-thermo-electronics. The large amount of heat generated in nanoscale devices is today one of the most fundamental obstacles for reducing the size of electronics. In this proposal we turn the problem around by instead using electrically controlled local heating of magnetic nano-circuits to achieve fundamentally new functionality, relevant to several key objectives of the information and communication technology. Particular emphasis will be put on investigating and technologically evaluating the interplay of spin, charge, and heat in magnetic structures of sub-10 nm dimensions. Such structures, although inaccessible by todays lithographic means, are in our view crucial for further miniaturization of electronic devices.

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