Physics of the Solid State最新文献

Polydiphenilenphtalide (PDP) belongs to organic dielectrics that demonstrate the electroconducting properties, when applying an external electrostatic field and/or mechanical stresses. In this work, the transport characteristics of thin-film lead–PDP–lead layered structures are studied in a wide temperature range. At quite high temperatures, current–voltage characteristics are adequately described in terms of the injection current model confirmed by a space charge. At temperatures below ~7.5 K, a number of the sample demonstrate peculiarities that can be explained by the effect of induced superconductivity in a thin film of a conducting polymer included between two massive superconductors (lead).

The convergence kinetics of S_A and S_B steps on Si(100) substrates with inclination of 0.5° and 0.1° are studied. To establish the character of the growth kinetics, the time dependences of the reflection high‑energy electron diffraction (RHEED) intensity are analyzed. It is shown that the convergence rate of the steps in the Si at a growth rate of 0.37 ML/s has a decreasing dependence with an increase temperature. It is found that the rate of formation of a single-domain surface increases with the width of terraces on the surface, which is likely to be related to a partial participation of the growth due to the formation of two-dimensional islands. At temperatures higher 650°С, the dominant growth mode due to the motion of the steps and the rate of formation of the single-domain surface decrease with an increase in the terrace width. Thus, the convergence of single-layer steps is determined by the conditions of the growth of the molecular-beam epitaxy (MBE) and also by the Si(100) substrate orientation. The convergence of S_A and S_B steps of the Si(100) surface is explained by a slow-down motion of S_A which is related to complex mechanisms of permeability and the formation of step kinks. It is assumed that the cause of the slow-down convergence the steps with increasing temperature is an increase in the kink density on the S_A step, which decreases the permeability coefficient of the S_A step.

Nanocrystalline CaSi films with thicknesses from 80 to 130 nm were grown on high-resistance silicon substrates with orientations (111) and (100) by the methods of low-temperature (190–330°C) molecular-beam epitaxy and low-temperature (330°C) solid-phase epitaxy, for which the microstructure, phase composition, and crystal structures were studied. It is found that the polycrystalline, nanocrystalline (NC), and amorphous CaSi and CaSi₂ films are characterized by preferential contribution of holes in the range 1.4–300 K. In magnetic fields 1–4 T and at temperatures 40–100 K, a giant linear magnetoresistive effect (MRE) (to 500%) was observed for the first time in CaSi films with the contribution of another CaSi₂ phase. In CaSi₂ film containing another phase (CaSi), peaks are detected on the temperature dependences of the resistivity and the Hall coefficient that correspond to a phase transition. In addition, in this film, the transition from the positive MRE to negative MRE is observed at Т = 120–200 K. This effect is not observed in the single-phase CaSi₂ film, which corresponds to a certain reconstruction of carrier flows in a magnetic field only in the two-phase system. The study of the thermoelectric properties of CaSi and CaSi₂ films shows that the semimetallic type of the conduction in them leads to the independence of the positive Seebeck coefficient Т = 330–450 K. It is found that the maximum contribution to the Seebeck coefficient and the power factor are observed in the amorphous CaSi film in the case of the presence of some fraction of NC Ca₂Si phase. In the single-phase CaSi₂ films, the Seebeck coefficient and the power factor are halved due to an increase in the hole concentration as compared to the CaSi films.

The temperature dependence of the specific heat of the CoFe₂O₄ ferromagnet and the 0.3CoFe₂O₄–0.7PbTiO₃ muliferroic composite is studied in the temperature range 150–820 K. An addition of lead titanate ferroelectric to cobalt ferrite ferromagnet is found to lead to a shift of the magnetic phase transition temperature to lower temperatures by 49 K and to a decrease in the specific heat in a wide temperature range. It is noted that the additional component of the specific heat is due to transitions of cobalt or iron ions to higher energy levels and also due to a distortion of the lattice parameters as a result of formation of three coexisting phases.

The effect of the current instability of hardening of a deformable medium element on the strain localization at different scale levels has been studied. The current instability term has been taken from the characteristic of the current instability of the electrical conductivity of semiconductors in strong electric fields with a specific I‒V curve [1]. A similar shape of the σ‒ε curve of hardening of a deformable medium element has been considered to be the cause of the strain localization. The strain localization phenomena caused by the current instability of different types have been discussed and modeled. It is shown that the plastic flow scenario under the current instability at the level of a microelement of a medium can manifest itself at the macroscale plastic flow level in the form of localizations of various types. The simulation within a two-level finite element model proposed previously in [2] has been carried out. The cases of a stable neck or neck propagation at the macrolevel under the uniaxial tension of a sample have been observed, depending on the shape of the hardening curves of the unit volume of a deformed sample similar the current instability curves.

The luminescent properties of Y_1 – xSc_xPO₄: 0.5 mol % Eu³⁺ (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1) solid solutions are studied at the excitation by the radiations of ultraviolet and vacuum-ultraviolet ranges. The disordering of the solid-solution crystal structure is shown to influence the structure of the Eu³⁺ luminescence spectra. The bandgap width is shown to nonlinearly depend on the solid solution composition. The model explaining this effect is proposed.

Consecutive stages of synthesizing epitaxial SiC films on n-type Si(111) and p-type Si(111) surfaces in a mixture of gaseous carbon monoxide and silane are studied by X-ray diffraction and Raman scattering methods. In films grown on an n-type Si(111) surface, only weak elastic deformations are observed during synthesis; however, in films grown on p-type Si substrates, relatively strong elastic deformations form, which are completely relaxed by the 40th min. It is found that the film structure is sharply changed at the third minute of the growth, which is related to the formation and growth of pores in the SiC layer. The differences of the lattice parameters of SiC films grown on n-Si and p-Si substrates are determined and confirmed by analyzing the change in the curvatures of the SiC/Si plates.

The paper presents the experimental investigation of the role of the size factor in the formation of the defect structure of metallic materials. The objects of study were polycrystalline FCC Cu–Al and Cu–Mn solid solutions with average grain sizes of 10–240 µm. The dislocation structure of foil samples subjected to various deformations at room temperature was studied by TEM. We measured the scalar dislocation density (ρ), the density of geometrically necessary dislocations (GND) (ρ_g), the density of statistically stored dislocations (SSD) (ρ_s), the curvature-torsion of the crystal lattice (χ), and some other parameters. The effect of the grain size of the dislocation substructure on its parameters has been quantitatively studied. The sources of curvature-torsion χ of the crystal lattice were determined from electron microscopic images. We measured χ in the alloys under study from different sources and its change with distance (x) from the source for alloys with fixed grain size and degree of deformation. The change in the average value of curvature-torsion from all sources with the degree of deformation is considered.

WC–Fe–Al coatings were obtained by the electrospark deposition of AISI304 stainless steel in an anode mixture of aluminum and iron granules with the addition of tungsten carbide powder. The coatings had a two-phase microstructure represented by an intermetallic Fe–Al matrix with large inclusions of tungsten carbide. Impedance spectrometry in 3.5% NaCl showed a decrease in the corrosion resistance of WC–Fe–Al coatings with an increase in the concentration of tungsten carbide in the anode mixture. Polarization tests showed that with an increase in the content of tungsten carbide in the anode mixture, the corrosion potential of coatings monotonically increased from –0.77 to –0.61 V. At the same time, the corrosion current density increased linearly from 19.4 to 62.7 µA/cm². High-temperature oxidation of coatings are intensified with an increase in the concentration of tungsten carbide at a temperature of 900°C for 100 h of testing, however, moderate reinforcement of the Fe–Al matrix with tungsten carbide did not worsen its oxidation resistance. With increase in the of reinforcing ceramic content in the Fe–Al coating, its microhardness increases from 7.3 to 11 GPa, the coefficient of friction decreases to 0.51 and wear resistance improves. The use of WC/Fe–Al coatings on AISI 304 stainless steel makes it possible to increase the hardness and oxidation resistance of steel surface, reduce the coefficient of friction, and improve wear resistance up to 19 times.