Том 58, № 4 (2016)

The electrophysical properties of Cd_xHg_1–xTe (x ≈ 0.3) films undoped and doped with indium during their growth were investigated. The as-grown films were subjected to heat treatment in mercury vapor. The magnetic field dependences of the Hall effect in the magnetic field range of 0.05–1.0 T at 77 K were explained by the fact that, in the films, there are two types of electrons with high and low mobilities. The analysis of the temperature dependences of the minority carrier lifetime in the range of 77–300 K revealed that the as-grown films contain two types of traps with different energies. It was found that annealing at a saturated mercury vapor pressure increases the minority carrier lifetime due to the suppression of recombination centers, which can be associated with growth defects in Cd_xHg_1–xTe/CdTe/Si heterostructures.

The structural state of a bulk Zn_0.95Fe_0.05Se cubic crystal grown by the chemical transport method from the gas phase has been investigated using thermal neutron diffraction at room temperature. It has been found that the measured neutron diffraction patterns of the crystal, in addition to structural Bragg peaks, contain a clearly identified system of superstructure reflections with the wave vector k = (1/3 1/3 1/3)2π/a (where a is the parameter of the cubic unit cell), which is interpreted as a clear evidence of the incipient transition state preceding the concentration phase transformation fcc ↔ hcp. It has been shown that the resulting structural state includes an inhomogeneous microstrain field with the possible appearance of long-wavelength modulations based on the initial sphalerite structure.

Single crystals Tb_1–xHo_xAl₃(BO₃)₄ with x = 0, 0.1, 0.5, 0.9, 1 have been grown based on bismuth trimolybdate using a solution–melt method. Their magnetic properties have been studied in the temperature range of 4.2–295 K and magnetic fields to 9 T. The effective magnetic moments μ_eff|| and μ_eff⊥ have been determined. It has been found that the temperature dependence of the susceptibility measured experimentally differs from that calculated on the assumption that the contributions of Tb³⁺ and Ho³⁺ ions are proportional to fractions from the susceptibilities of TbAl₃(BO₃)₄ and HoAl₃(BO₃)₄, respectively.

The magnetorefractive effect (MRE) in manganites has been studied within the effective medium theory. The MRE has been calculated in manganites La_1–xK_xMnO₃ (x = 0.1 and 0.15) for light transmission and reflection. Good agreement with experimental results demonstrates direct relation of the MRE to the magnetoresistance and optical properties of manganites with various substitution levels. It has been shown that the MRE can exceed 10% in the near- and mid-IR region near the magnetic phase transition and can change sign during light transmission and reflection in the region of phonon modes. The results make it possible to recommend the MRE as a contactless method for studying magnetoresistive materials and for developing sensors and microelectronic elements.

The specific heat and dielectric permittivity of Bi_1–xSm_xFeO₃ (x = 0–0.30) multiferroics have been studied in the temperature range of 300–800 K. A slight substitution of bismuth with samarium is established to cause a considerable shift in the antiferromagnetic phase transition temperature and to an increase in the specific heat over a wide temperature range. Other anomalies typical of phase transitions have been found in the temperature dependences of the specific heat and dielectric permittivity for the compounds with x = 0.10 and 0.15 at T ≈ 735 and 495 K, respectively. The results of the studies of the specific heat have been discussed together with the data of the structural investigations.

The inhomogeneous strain induced by a homogeneous external electric field (the converse flexoelectric effect) has been studied in a thin BaTiO₃ single crystal slab. The type of inhomogeneous strain (cylindrical and spherical bending) has been determined via the interference method, and its dependence on the applied filed is measured, as well. The influence of the domain structure on this effect has also been shown.

The dynamics of kink solitons is very sensitive to random irregularities of the potential relief. The evolution of kinks after their generation is essentially modified by strong fluctuations of the potential. The stochastic nature of such modification is taken into account by the theory of extreme deviations on a random walk.

The microdeformation has been investigated under uniaxial compression of beech-derived biocarbons partially graphitized during carbonization in the presence of a Ni- or Fe-containing catalyst. The strength and ultimate fracture strain have been determined at different temperatures of carbonization of the samples in the absence or in the presence of a catalyst. It has been shown using high-precision interferometry that the deformation of biocarbon samples under uniaxial loading occurs through jumps (in magnitude and rate of deformation) with axial displacements in the nanometer and micrometer ranges. The use of a catalyst leads to a decrease in the size of nanometer-scale jumps and in the number of micrometer-scale jumps. The standard deviations of the strain rate on loading steps from the smooth average dependence of the strain rate on the displacement have been calculated for micrometer-scale jumps. A similar characteristic for nanometer- scale jumps has been determined from the distortion of the shape of beats in the primary interferogram. It has been shown that the variation in the standard deviation of the strain rate with a change in the carbonization temperature is similar to the corresponding dependence of the ultimate fracture strain.

This paper reports on the results of the investigation of electrically active defects in the crystal structure in a layered ferroelectric–semiconductor TlInS₂: La crystal by photoinduced current transient spectroscopy (PICTS). It has been found that there are states of the crystal that differ in the magnitude of the photoresponse varying within four orders of magnitude, which is interpreted in terms of the differences in states of the domain structure of the crystal. The specific features of the recording of thermal emission from defects in the presence of an additional contribution from the photovoltaic component of the response of the crystal to excitation with light have been discussed.

This paper reports on the formation of complexes consisting of isolated free-standing crystalline semiconductor quantum dots, for example, nc-Si/SiO₂, functionalized by short oligonucleotides, for example, the single-stranded system d(20G, 20T). Here, d are deoxyribonucleotides, G and T are guanine and thymine nucleotides, respectively. It has been found that these complexes are unique objects for the elucidation of the specific features in the manifestation of new quantum-size effects in biomacromolecules. It has been demonstrated that the possibility exists of detecting and recording, in such complexes of biomacromolecules, spectrally selective resonance enhancement of Raman scattering intensity in fluctuations of nucleotide molecules due to coherent nonradiative transfer of a photoexcited electron and a hole at the interface of the complex. This dynamic optical imaging of spectral responses can be of applied interest for the development of nanobiophotonic technologies.

Decomposition of a homogeneous intercalation compound with the formation of inclusions in the interlayer space of a matrix lattice has been directly observed. In full compliance with previously advanced theoretical concepts, it has been shown that the decomposition is accompanied by metallic iron extraction, which then gradually transforms into iron selenide due to the interaction with gaseous selenium.The hierarchy of diffusion mobilities of various defects in Fe_xTiSe₂ intercalation compound has been determined. It has been found that the largest mobility is inherent to intrinsic defects of the TiSe₂ lattice, i.e., vacancies in Ti and Se sublattices. The phenomenon of dissociation pressure oscillations as a function of time has been detected. This phenomenon has been explained by the existence of a slow decomposition stage, i.e., intercalated iron diffusion during the formation and dissolution of its inclusions as an individual phase.

The transition from incomplete to complete grain boundary wetting in copper alloys with 2.2 and 4.9 wt % Co has been studied. These alloys with peritectic phase diagrams differ from previously studied systems with eutectic transformation by the fact that the melt layer separating grains from each other is not enriched, but is depleted by the second component (cobalt in this case). The fraction of completely wetted grain boundaries increases with temperature, as in eutectic systems, from zero at a temperature of 1098°C to ~80% at 1096°C. For symmetric twin boundaries, the temperature dependence of the contact angle with melt drops is constructed. As in the eutectic systems, the contact angle decreases with increasing temperature (although not to zero due to the extremely low energy of symmetric twin boundaries).

Deposited electrocatalysts with different distributions of components in PtCu bimetallic nanoparticles involved in their composition were synthesized by simultaneous and sequential reduction of Cu(2+) and Pt(IV) in a carbon suspension. The dependence of the atomic structure of PtCu nanoparticles on the synthesis conditions and the degree of influence of post-treatment was established from analysis of the changes in Fourier transforms of the experimental Pt and Cu EXAFS spectra, as well as the structural parameters obtained by their fitting before and after the treatment of the materials in an acid solution. A technique was proposed for visualizing the atomic structure of synthesized bimetallic nanoparticles. This technique made it possible to determine the character of the distribution of the components over the nanoparticle volume in accordance with the component composition and local atomic structure parameters determined from EXAFS spectroscopy and to obtain the visualization of the distribution of the components in PtCu nanoparticles synthesized by the aforementioned methods.

In situ measurements of the magnetic susceptibility of ordered and disordered titanium monoxides TiO_y in the temperature range from 300 to 1200 K have revealed that it depends on the size of crystals, their stoichiometry, and long-range order parameters. Analysis of the data for both the ordered and disordered TiO_y has demonstrated that the dependence of the Van Vleck paramagnetism on the nanocrystal size is inversely proportional due to the breaking of symmetry of the local environment of titanium and oxygen atoms near the surface of nanocrystals. It has been found that the Van Vleck contribution from the atomic vacancy disorder in monoxide nanocrystals of superstoichiometric composition, as well as in the crystalline stoichiometric monoxide, is proportional to the deviation of the degree of long-range order from the maximum value.

A new theoretical (semiempirical) model of diffusion-drift charge carrier transport in layers with a fractal structure based on a partial differential equation with a fractional time derivative has been proposed. It has been shown by numerical calculations that a decrease in the order of the fractional derivative in the presence of the external electric field leads to broadening and asymmetry of the spatial distributions of charge carriers, which physically corresponds to intensification of scattering processes.

Analytical expressions for densities of states of free graphene-like A_NB_8–N compounds and flat and buckled epitaxial monolayers on a metallic substrate have been obtained by the tight-binding method using a low-energy approximation. Characteristic features of the densities of states as functions of the layer–substrate coupling constant and the buckling factor have been analyzed. The energy gaps and the binding energy between the epitaxial layer and the substrate have been estimated.

The mechanism and kinetics of anode destruction of {111} polar planes of n-GaAs and morphological features of forming oxide films in the potentiostatic mode of polarization in weakly acid solutions of electrolytes have been studied. It has been found that anode polarization of the gallium plane (111) Ga provides the formation of a porous structure of both the single-crystal matrix and oxide film, which has a planar topology. In this case, the pore density is always commensurable with the surface dope concentration. In contrast to the gallium plane, the anode polarization of the arsenic plane \(\overline {\left( {111} \right)} \) As provides the tangential mechanism of destruction of the semiconductor matrix and the island-type morphology of the oxide. Equal crystallographic orientation of islands is determined by the directive action of the family of oxidized planes \(\left\{ {1\overline {11} } \right\}\) GaAs. However, regardless of the crystallographic orientation of the polar plane, the forming oxide is represented by polycrystalline As₂O₃ and amorphous Ga₂O₃.

In polymer crystals (in particular, polyethylene), changes in the axial and contour lengths of skeletal interatomic bonds in chain molecules under mechanical loading (stretching) and heat treatment (heating) were measured using X-ray diffractometry and Raman spectrometry. The performed analysis of the measured force and temperature dependences gave theoretical descriptions of the deformation of a polymer crystal (the confirmation of the data available in the literature for mechanical loading and an original development for heating). The components of the potential energy of a deformed polymer crystal were determined both for stretching of skeletal bonds and for bending of chain molecules. It was found that there is a significant difference in the ratios of these components for a deformed polymer crystal under mechanical loading and during heating.

The initial stage of stress relaxation, i.e., a decrease of the stress with time in an extended solid at a fixed length of the specimen, has been studied in oriented fibers of a linear polymer, polypropylene, chosen as the object of investigation. Experimental data have been obtained, and the stress in the object from the beginning of tensile loading of the specimen has been analyzed. It has been found that the stress relaxation caused by thermal fluctuation conformational transitions in stretched chain polymer molecules occurs from the beginning of the stretching of the polymer fiber. The time dependence of the stress relaxation of polypropylene fibers in all initial stages of deformation of the fibers has been elucidated.

Dynamics of disordering of graphene upon heating has been studied by computer simulation. The mechanism governing the formation of seeds for a three-dimensional grid of entangled carbon chains into which graphene is transformed upon melting has been analyzed in detail. It has been shown that the emergence of these seeds is preceded by the disruption of several interatomic bonds, accompanied with the formation of large rings or groups of adjacent rings and the formation of penta- and heptagons of their C–C bonds. The results of this work on the whole agree with the Lindemann–Lozovik criterion. The melting temperature is estimated as T_m ~ 5100 K.

The thermal conductivity of a ZnWO₄ single crystal in the principal crystallographic directions has been studied experimentally in the temperature range of 50–573 K, and the heat capacity of the single crystal has been measured in the range of 81–301 K.