Microporous and mesoporous carbon nanostructures with the inverse opal lattice

The conditions for porous structure formation in carbon nanostructures with the inverse opal lattice have been studied. The characteristics of the porous structure have been determined by means of the gas adsorption-desorption. The morphology and structure of samples have been examined using high-resolution transmission electron microscopy.     

Defect-induced instability of the surface layer involving static coupled Lamb and Rayleigh waves as a universal mechanism of the formation of an ensemble of nanodot nucleation centers

It is demonstrated that a stressed flat surface nanolayer saturated with mobile point defects exhibits a threshold (with respect to the defect concentration or mechanical stress) transition to a periodic spatially bent state with a simultaneous formation of the spatially periodic defect pile-ups at the extrema of the spontaneously emerging surface relief. In this case, the layer deformation corresponds to the displacements in a static bending Lamb wave and the deformation of the underlying elastic continuum corresponds to the displacements in the static Rayleigh wave. For the first time, we demonstrate that the analysis simultaneously involving the nonlocal character of the defect interaction with the lattice atoms and both (normal and lateral) defect-induced forces that cause the bending of the surface layer yields two maxima on the curve of the instability growth rate versus the period of the generated relief. This corresponds to the experimentally observed two scales of the surface relief modulation upon the laser and ion irradiation of semiconductors. Based on the results obtained, we propose a cooperative defect-deformational (DD) mechanism for the formation of an ensemble of the nanoparticle nucleation centers above the critical levels of the stress or the defect concentration. An approach to the calculation of a bimodal distribution function of the nanoparticle nucleation centers with respect to their size is adequately developed to the DD mechanism of nucleation which represents the distribution function in terms of the growth rate. The calculated results are compared with the experimental data for the molecular beam epitaxy of the nanodot ensemble and the pulsed laser nanostructuring of a solid surface.     

Formation and evolution of nanostructures on semiconductor surfaces in the process of laser-induced inelastic deformation

A hierarchy of formed Ge surface relief nanostructures, including a disordered nanocluster structure, a two-dimensional lattice, and a one-dimensional lattice, is observed as the laser irradiation dose is increased. It is described in the framework of the defect deformation mechanism.     

Synthesis,structure, and conduction of solid solutions BIMEVOX (Me = Cu,Ti)

Conditions for synthesizing single-phase solid solutions Bi₄V_{2 ? x} Cu _x/2Ti _x/2O_{11 ? x} and Bi_{4 ? x/2}V_{2 ? x/2}Cu _x/2Ti _x/2O_{11 ? x/2} are studied. The sequence of phase transformations is determined. Possible domains of stability of polymorphic modifications and the overall conductivity as a function of temperature and composition are studied. The structure of the γ-modification is refined using Rietveld’s full-profile analysis.     

A Lightweight Flexible Solar Cell Based on a Heteroepitaxial InGaP/GaAs Structure

Technical Physics - Problems arising in fabrication of lightweight flexible solar cells based on heteroepitaxial AIIIBV structures with substrate etching are discussed. Possible solutions are...     

Synthesis of α -SiC nanocrystals by carbothermal reduction of spherical nanoparticles of amorphous silicon dioxide

The method for carbothermal reduction of spherical particles of amorphous silicon dioxide is developed, and hexagonal α-SiC polytype nanocrystals are synthesized. The prepared samples are characterized by X-ray diffraction, Raman spectroscopy, photoluminescence spectroscopy, and electron microscopy. The silicon carbide nanocrystals prepared have sizes in the range 5–50 nm depending on the diameter of initial silicon dioxide particles. A detailed analysis of the positions of the lines in the Raman spectra, their broadening, and shift makes it possible to reliably establish that the samples under investigation predominantly contain the 6H and 4H silicon carbide polytypes and insignificant amounts of the 2H and 3C phases. The 15R and 21R polytypes in the samples are absent. It is noted that the samples are characterized by a substantial size effect: the luminescence intensity of small silicon carbide nanocrystals is more than three times higher than that of large SiC nanocrystals.     

The thermodynamic properties of DL- and L-lactides

The enthalpies of formation of DL-lactide and L-lactide, cyclic esters of lactic acid, were determined by combustion calorimetry. The transfer method was used to measure their vapor pressures and obtain the enthalpies of sublimation. A conformational analysis of lactides was performed, and the most stable conformations were determined. The equilibrium structures of lactides, sets of fundamental vibrations, moments of inertia, and total energies of the most stable conformers were calculated quantum-chemically at the B3LYP/6-311++G(3df,3pd) level. The G3MP2 composite method was used to estimate the enthalpies of formation of lactides in the gas phase. The thermodynamic properties of lactides in the ideal gas state were calculated over the temperature range 100–1500 K.     

A study of polarization in smectic liquid crystals via statistical-physics methods

The spontaneous polarization processes in synclinic and anticlinic smectic liquid crystals are discussed in the context of molecular statistical theory. The effects of interaction between molecules, external electric fields, and bending of molecules via polarization are elucidated as well.