arXiv subjects

V. A. Osipov

Publications and source records attributed to V. A. Osipov.

At least 19 recordsLinked to original sources

arXiv2025

Phonon-Limited Mobility in H/F-functionalized Nanotubes with 1D $π$-chains

Electron mobility due to electron-phonon interaction is investigated for fully fluorinated/hydrogenated zig-zag carbon nanotubes containing one-dimensional alternating chains of carbon atoms with $π$-bonds. The behavior of mobility associated with changes in the tube diameter, coating type (F/H) and temperature is revealed. In particular, it is shown that the dependence of mobility on the diameter in such tubes is periodic with the chirality index, which is associated with the absence of scattering on TA phonons in the tubes with an even number of conducting chains due to mirror symmetry. The obtained small values of phonon-limited mobility indicate that tubes with one-dimensional conducting chains are more promising for use as gas sensors than as elements of electronic devices. Calculations are performed within the self-energy relaxation time approximation (SERTA) using the non-orthogonal tight-binding approach.

cond-mat.mes-hall↗

arXiv2022

Electrical Resistivity of Polycrystalline Graphene: Effect of Grain-Boundary-Induced Strain Fields

We have revealed the decisive role of grain-boundary-induced strain fields in electron scattering in polycrystalline graphene. To this end, we have formulated the model based on Boltzmann transport theory which properly takes into account the microscopic structure of grain boundaries (GB) as a repeated sequence of heptagon-pentagon pairs. The effect of strain field is described within the deformation potential theory. For comparison, we consider the scattering due to electrostatic potential of charged grain boundary. We show that at naturally low GB charges the deformation potential scattering dominates and leads to physically reasonable and, what is important, experimentally observable values of the electrical resistivity. It ranges from 0.1 to 10 k$Ω$$μ$m for different types of GBs with a size of 1 $μ$m and has a strong dependence on misorientation angle. For low-angle highly charged GBs, two scattering mechanisms may compete. The resistivity increases markedly with decreasing GB size and reaches values of 60 k$Ω$$μ$m and more. It is also very sensitive to the presence of irregularities modeled by embedding of partial disclination dipoles. With significant distortion, we found an increase in resistance by more than an order of magnitude, which is directly related to the destruction of diffraction on the GB. Our findings may be of interest both in the interpretation of experimental data and in the design of electronic devices based on poly- and nanocrystalline graphene.

cond-mat.mtrl-sci↗

arXiv2020

Jump of tunneling magnetoresistance in magnetic nanocontacts with mismatched cross section

We have studied the influence of the transverse size of a magnetic tunnel nanojunction on the magnitude of the magnetoresistance. During modeling, the size of the right contact was fixed, while the size of the left one gradually changed until they coincided. We found a sharp drop in the tunneling magnetoresistance (TMR) in nanocontacts with mismatched cross section. This can be explained by the peculiarities of the spatial distribution of the electron density, which is different for majority and minority-spin states. The discovered effect must be taken into account in the design of TMR-based nanodevices.

cond-mat.mes-hall↗

arXiv2019

Electron-hole asymmetry in electrical conductivity of low-fluorinated graphene: Numerical study

By using the real-space Green-Kubo formalism we study numerically the electron transport properties of low-fluorinated graphene. At low temperatures the diffuse transport regime is expected to be prevalent, and we found a pronounced electron-hole asymmetry in electrical conductivity as a result of quasi-resonant scattering on the localized states. For the finite temperatures in the variable-range hopping transport regime the interpretation of numerical results leads to the appearance of local minima and maxima of the resistance near the energies of the localized states. A comparison with the experimental measurements of the resistance in graphene samples with various fluorination degrees is discussed.

cond-mat.mes-hall↗

arXiv2019

Impact of grain boundary characteristics on thermal transport in polycrystalline graphene: Analytical results

The effect of grain boundary (GB) structure, size and shape on thermal conductivity of polycrystalline graphene is studied in the framework of the deformation potential approach. Precise analytical expressions for the phonon mean free path (MFP) are obtained within the Born approximation. We found exactly two types of behavior in the long-wavelength limit: MFP varies as $k^{-1}$ for open GBs of any shape while it behaves as $k^{-3}$ for closed configurations (loops). In the short-wavelength limit MFP tends to a constant value for any configuration. Oscillatory behavior is observed for all GBs which indicates that they serve as diffraction grating for phonons. This property is also inherent in GBs with irregularities caused by partial disclination dipoles. The thermal conductivity is calculated in the framework of Callaway's approach with all main sources of phonon scattering taken into account. Reduction of the heat conductivity with decreasing grain size is obtained in a wide temperature range. Most interesting is that we found a marked decrease in the thermal conductivity of polycrystalline graphene containing GBs with changes in their misorientation angles.

cond-mat.mtrl-sci↗

arXiv2019

The structure of deterministic mass and surface fractals: theory and methods of analyzing small-angle scattering data

Small-angle scattering (SAS) of X-rays, neutrons or light from ensembles of randomly oriented and placed deterministic fractal structures are studied theoretically. In the standard analysis, a very few parameters can be determined from SAS data: the fractal dimension, and the lower and upper limits of the fractal range. The self-similarity of deterministic structures allows one to obtain additional characteristics of their spatial structures. The paper considers models which can describe accurately SAS from such structures. The developed models of deterministic fractals offer many advantages in describing fractal systems, including the possibility to extract additional structural information, an analytic description of SAS intensity, and effective computational algorithms. Generalized Cantor fractals and few of its variants are used as basic examples to illustrate the above concepts and to model physical samples with mass, surface, and multi-fractal structures. The differences between the deterministic and random fractal structures in analyzing SAS data are emphasized. Several limitations are identified in order to motivate future investigations of deterministic fractal structures.

cond-mat.soft↗

arXiv2017

Effect of edge vacancies on performance of planar graphene tunnel field-effect transistor

The influence of edge vacancies on the working ability of the planar graphene tunnel field-effect transistor (TFET) is studied at various concentrations and distributions (normal, uniform, periodic) of defects. All calculations are performed by using the Green's function method and the tight-binding approximation. It is shown that the transistor performance depends critically on two important factors associated with the defects: the destruction of the edge-localized electronic states and the emergence of subpeaks near the Fermi level. The supportable operation conditions of the TFET are found to be ensured at 30 percent or less of edge vacancies regardless of the type of their distribution.

cond-mat.mtrl-sci↗

arXiv2016

Small-angle scattering from the Cantor surface fractal on the plane and the Koch snowflake

The small-angle scattering (SAS) from the Cantor surface fractal on the plane and Koch snowflake is considered. We develop the construction algorithm for the Koch snowflake, which makes possible the recurrence relation for the scattering amplitude. The surface fractals can be decomposed into a sum of surface mass fractals for arbitrary fractal iteration, which enables various approximations for the scattering intensity. It is shown that for the Cantor fractal, one can neglect with a good accuracy the correlations between the mass fractal amplitudes, while for the Koch snowflake, these correlations are important. It is shown that nevertheless, the correlations can be build in the mass fractal amplitudes, which explains the decay of the scattering intensity $I(q)\sim q^{D_{\mathrm{s}}-4}$ with $1 < D_{\mathrm{s}} < 2$ being the fractal dimension of the perimeter. The curve $I(q)q^{4-D_{\mathrm{s}}}$ is found to be log-periodic in the fractal region with the period equal to the scaling factor of the fractal. The log-periodicity arises from the self-similarity of sizes of basic structural units rather than from correlations between their distances. A recurrence relation is obtained for the radius of gyration of Koch snowflake, which is solved in the limit of infinite iterations. The present analysis allows us to obtain additional information from SAS data, such as the edges of the fractal regions, the fractal iteration number and the scaling factor.

cond-mat.stat-mech↗

arXiv2016

Anomalous Tunneling Systems in Amorphous Organic Materials

We compare the heat release data of organic glasses with that of amorphous and glass like crystalline solids. Anomalous behavior was found in all these materials, which disagrees with the standard tunneling model. We can explain the most of the experimental observations within a phenomenological model, where we assume that for a part of tunneling systems the barrier heights are strongly reduced as a consequence of the local stress produced during the cooling process.

cond-mat.dis-nn↗

arXiv2016

Anomalous Isotopic Effect of Tunneling States in NbTi-H/D

The thermal conductivity, heat capacity and heat release of NbTi, NbTi-H and NbTi-D were measured at low temperatures. All three systems reveal low temperature anomalies typical for structural glasses. It is shown that above a concentration of 2\% H or D the tunneling states of the NbTi matrix disappear. Therefore, for higher concentration it is a good system to proof how the change of the mass of tunneling atoms influences the low temperature anomalies. For the heat capacity we found the expected isotopic effect. However, the anomalous isotopic effect observed for the heat release data cannot be explained within the standard tunneling model. A surprising result is that tunneling systems with very high barrier heights, even the systems with the maximum barrier height, influence remarkable the heat capacity and the heat release data at low temperatures. As a possible origin, we consider large-scale fluctuations in thermal expansion which could generate anomalous two-level systems.

cond-mat.dis-nn↗

arXiv2016

Relaxation time spectrum of low-energy excitations in one- and two-dimensional materials with charge or spin density waves

The long-time thermal relaxation of (TMTTF)$_2$Br, Sr$_{14}$Cu$_{24}$O$_{41}$ and Sr$_2$Ca$_{12}$Cu$_{24}$O$_{41}$ single crystals at temperatures below 1 K and magnetic field up to 10 T is investigated. The data allow us to determine the relaxation time spectrum of the low energy excitations caused by the charge-density wave (CDW) or spin-density wave (SDW). The relaxation time is mainly determined by a thermal activated process for all investigated materials. The maximum relaxation time increases with increasing magnetic field. The distribution of barrier heights corresponds to one or two Gaussian functions. The doping of Sr$_{14-x}$Ca$_{x}$Cu$_{24}$O$_{41}$ with Ca leads to a drastic shift of the relaxation time spectrum to longer time. The maximum relaxation time changes from 50 s (x = 0) to 3000 s (x = 12) at 0.1 K and 10 T. The observed thermal relaxation at x=12 clearly indicates the formation of the SDW ground state at low temperatures.

cond-mat.mtrl-sci↗

arXiv2016

The effect of electron-phonon interaction on the thermoelectric properties of defect zigzag nanoribbons

Thermoelectric properties of graphene nanoribbons with periodic edge vacancies and antidot lattice are investigated. The electron-phonon interaction is taken into account in the framework of the Hubbard-Holstein model with the use of the Lang-Firsov unitary transformation scheme. The electron transmission function, the thermopower and the thermoelectric figure of merit are calculated. We have found that the electron-phonon interaction causes a decrease in the peak values of the thermoelectric figure of merit and the shift of the peak positions closer to the center of the bandgap. The effects are more pronounced for the secondary peaks that appear in the structures with periodic antidot.

cond-mat.mtrl-sci↗

arXiv2016

Scattering from surface fractals in terms of composing mass fractals

We argue that a finite iteration of any surface fractal can be composed of mass-fractal iterations of the same fractal dimension. Within this assertion, the scattering amplitude of surface fractal is shown to be a sum of the amplitudes of composing mass fractals. Various approximations for the scattering intensity of surface fractal are considered. It is shown that small-angle scattering (SAS) from a surface fractal can be explained in terms of power-law distribution of sizes of objects composing the fractal (internal polydispersity), provided the distance between objects is much larger than their size for each composing mass fractal. The power-law decay of the scattering intensity $I(q) \propto q^{D_{\mathrm{s}}-6}$, where $2 < D_{\mathrm{s}} < 3$ is the surface fractal dimension of the system, is realized as a non-coherent sum of scattering amplitudes of three-dimensional objects composing the fractal and obeying a power-law distribution $d N(r) \propto r^{-τ} dr$, with $D_{\mathrm{s}}=τ-1$. The distribution is continuous for random fractals and discrete for deterministic fractals. We suggest a model of surface deterministic fractal, the surface Cantor-like fractal, which is a sum of three-dimensional Cantor dusts at various iterations, and study its scattering properties. The present analysis allows us to extract additional information from SAS data, such us the edges of the fractal region, the fractal iteration number and the scaling factor.

cond-mat.stat-mech↗

arXiv2016

Effect of edge vacancies on localized states in semi-infinite zigzag graphene sheet

The effect of vacancies on the robustness of zero-energy edge electronic states in zigzag-type graphene layer is studied at different concentrations and distributions of defects. All calculations are performed by using the Green's function method and the tight-binding approximation. It is found that the arrangement of defects plays a crucial role in the destruction of the edge states. We have specified a critical distance between edge vacancies when their mutual influence becomes significant and affects markedly the density of electronic states at graphene edge.

cond-mat.mtrl-sci↗

arXiv2016

Enhancement of thermoelectric figure of merit in zigzag graphene nanoribbons with periodic edge vacancies

The influence of periodic edge vacancies and antidot arrays on the thermoelectric properties of zigzag graphene nanoribbons is investigated. Using the Green's function method, the tight-binding approximation for the electron Hamiltonian and the 4th nearest neighbor approximation for the phonon dynamical matrix, we calculate the Seebeck coefficient and the thermoelectric figure of merit. It is found that, at a certain periodic arrangement of vacancies on both edges of zigzag nanoribbon, a finite band gap opens and almost twofold degenerate energy levels appear. As a result, a marked increase in the Seebeck coefficient takes place. It is shown that an additional enhancement of the thermoelectric figure of merit can be achieved by a combination of periodic edge defects with an antidot array.

cond-mat.mtrl-sci↗

arXiv2015

Effect of Stone-Wales defects on the thermal conductivity of graphene

The problem of phonon scattering by strain fields caused by Stone-Wales (SW) defects in graphene is studied in the framework of the deformation potential approach. An explicit form of the phonon mean free path due to phonon-SW scattering is obtained within the Born approximation. The mean free path demonstrates a specific $q$-dependence varying as $q^{-3}$ at low wavevectors and taking a constant value at large $q$. The thermal conductivity of graphene nanoribbons (GNRs) is calculated with the three-phonon umklapp, SW and rough edge scatterings taken into account. A pronounced decrease of the thermal conductivity due to SW defects is found at low temperatures whereas at room temperatures and above the phonon-phonon umklapp scattering becomes dominant. A comparison with the case of vacancy defects shows that they play more important role in the reduction of the thermal conductivity in GNRs over a wide temperature range.

cond-mat.mtrl-sci↗

arXiv2014

Planar graphene tunnel field-effect transistor

We propose a concept for a graphene tunnel field-effect transistor. The main idea is based on the use of two graphene electrodes with zigzag termination divided by a narrow gap under the influence of the common gate. Our analysis shows that such device will have a pronounced switching effect at low gate voltage and high on/off current ratio at room temperature.

cond-mat.mes-hall↗

arXiv2013

Small-angle scattering from multi-phase fractals

Small-angle scattering (SAS) intensities observed experimentally are often characterized by the presence of successive power-law regimes with various scattering exponents whose values vary from -4 to -1. This usually indicates multiple fractal structures of the sample characterized by different size scales. The existing models explaining the crossover positions (that is, the points where the power-law scattering exponent changes) involve only one contrast parameter, which depends solely on the ratio of the fractal sizes. Here, a model that describes SAS from a multi-phase system with a few contrast parameters is described, and it is shown that the crossover position depends on the scattering length density of each phase. The Stuhrmann contrast variation method is generalized and applied to experimental curves in the vicinity of the crossover point beyond the Guinier region. The contrast variation is applied not to the intensity itself but to the model parameters, which can be found by fitting the experimental data with the suggested interpolation formula. The model supplements the existing two-phase models and gives the simple condition of their inapplicability: if the crossover point depends on the contrast then a two-phase model is not relevant. The developed analysis allows one to answer the qualitative question of whether one fractal `absorbs' another one or they are both immersed in a surrounding homogeneous medium like a solvent or solid matrix. The models can be applied to experimental SAS data where the absolute value of the scattering exponent of the first power-law regime is higher than that of the subsequent second power-law regime, that is, the scattering curve is `convex' near the crossover point. As is shown, the crossover position can be very sensitive to contrast variation, which influences significantly the length of the fractal range.

cond-mat.stat-mech↗