[en] This paper reviews research into the electrical properties that are imparted to composite materials by introducing carbon nanotubes (CNTs) into their polymer matrices. Due to the large aspect ratio of CNTs, even a small amount of doping (at a level of 0.01 - 0.1%) is enough to increase the conductivity of the material by more than ten orders of magnitude, thus changing it from an insulator to a conductor. At low doping, charge transfer is of a percolation nature in the sense that nanotubes that are in contact with each other form conducting channels in the material. Importantly, the conductivity has a threshold nature, so that the conduction jump occurs upon an arbitrarily small increase in a doping level above the critical value. This paper summarizes experimental data on the position of the percolation threshold and the maximum magnitude of the conductivity for composites obtained using various polymer types and a variety of CNT geometries. Factors affecting the electrical characteristics of composites produced by distinct methods are analyzed. Methods for and basic results obtained from the simulation of the percolation conductivity of CNT-doped composites are discussed. Particular attention is given to contact phenomena that occur at adjacent nanotube boundaries and which determine the conductivity of CNT-doped composites. (reviews of topical problems)

[en] Based on the equation of motion of an antiferromagnetic moment, taking into account a random field of thermal fluctuations, we propose a Monte Carlo (MC) scheme for the numerical simulation of the evolutionary dynamics of an antiferromagnetic particle, corresponding to the Langevin dynamics in the Kramers theory for the two-well potential. Conditions for the selection of the sphere of fluctuations of random deviations of the antiferromagnetic vector at an MC time step are found. A good agreement with the theory of Kramers thermal relaxation is demonstrated for varying temperatures and heights of energy barrier over a wide range of integration time steps in an overdamped regime. Based on the developed scheme, we performed illustrative calculations of the temperature drift of the exchange bias under the fast annealing of a ferromagnet–antiferromagnet structure, taking into account the random variation of anisotropy directions in antiferromagnetic grains and their sizes. The proposed approach offers promise for modeling magnetic sensors and spintronic memory devices containing heterostructures with antiferromagnetic layers. (paper)

[en] The structure and elastic properties of (5,5) and (10,10) nanotubes, as well as barriers for relative rotation of the walls and their relative sliding along the axis in a double-walled (5,5)-(10,10) carbon nanotube, are calculated using the density functional method. The results of these calculations are the basis for estimating the following physical quantities: ultimate shear strengths and diffusion coefficients for relative sliding along the axis and rotation of the walls, as well as frequencies of relative rotational and translational oscillations of the walls. The commensurability-incommensurability phase transition is analyzed. The length of the incommensurability defect is estimated on the basis of ab initio calculations. It is proposed that a double-walled carbon nanotube be used as a plain bearing. The possibility of experimental verification of the results is discussed

[en] The tribological characteristics of nanotube-based nanoelectromechanical systems (NEMS) exemplified by a gigahertz oscillator are studied. Various factors that influence the tribological properties of nanotube-based NEMS are quantitatively analyzed with the use of molecular dynamics calculations of the quality factor (Q-factor) of the gigahertz oscillator. We demonstrate that commensurability of the nanotube walls can increase the dissipation rate, while the structure of the wall ends and the nanotube length do not influence the Q-factor. It is shown that the dissipation rate depends on the interwall distance and the way of fixation of the outer wall, and is significant in the case of a poor fixation for nanotubes with a large interwall distance. Defects are found to strongly decrease the Q-factor due to the excitation of low-frequency vibrational modes. No universal correlation between the static friction forces and the energy dissipation rate is established. We propose an explanation of the obtained results on the basis of the classical theory of vibrational-translational relaxation. Significant thermodynamics fluctuations are revealed in the gigahertz oscillator by molecular dynamics simulations and they are analyzed in the framework of the fluctuation-dissipation theorem. The possibility of designing NEMS with a desirable Q-factor and their applications are discussed on the basis of the above results.

[en] A new method is proposed for controlling the motion of nanoelectromechanical systems based on carbon nanotubes. In this method, a single-walled nanotube acquires an electric dipole moment owing to the chemical adsorption of atoms or molecules at open ends of the nanotube. The electric dipole moments of carbon nanotubes with chemically modified ends are calculated by the molecular orbital method. These nanotubes can be set in motion under the effect of a nonuniform electric field. The possibility of controlling the motion of nanoelectromechanical systems with the proposed method is demonstrated using a nanotube-based gigahertz oscillator as an example. The operating characteristics of the gigahertz oscillator are analyzed, and its operation is simulated by the molecular dynamics method. The controlling parameters and characteristics corresponding to the controlled operating conditions at a constant frequency for the system under investigation are determined