Stresses and strains arising from the mesoscopic mismatch at interfaces may affect in diverse ways the properties of surfaces and deposited nanostructures. The reasons for the occurrence of mesoscopic mismatch on metal surfaces and its consequences are briefly reviewed. It is shown how this mismatch affects the growth, structure, and morphology of thin films and nanostructures in the early stages of epitaxy.
The main interaction reactions in the Al2O3−N2 system are determined for a temperature of 2400 K and pressure of 1 bar. It is found that, in the absence of direct interaction of nitrogen (molecular and atomic) with the melt, chemical reactions may occur between nitrogen and the products of Al2O3 melt dissociative evaporation. The reactions of nitrogen oxidation and the interaction reactions between nitrogen oxides and the melt, both direct and with participation of elementary oxygen or gaseous aluminum oxides, are determined. It is shown that the elementary nitrogen forms may interact with melt jointly with nitrogen oxides and (or) with all Al-containing components of the system. The concentrations of the gaseous materials that are in equilibrium with Al2O3 are calculated by the Monte Carlo method.
The specific features of aluminum localization and the mechanism of formation of donor centers in ZnO:Al layers synthesized by rf magnetron sputtering have been investigated. It is shown that aluminum is mainly localized on intergranular boundaries of zinc oxide in the intrinsic oxide phase. The mechanism of Al oxidation on grain boundaries depends strongly on the oxygen content in the working chamber: during sputtering in a pure argon atmosphere with oxygen deficit, aluminum oxidation occurs as a result of the interaction of the surface layer of zinc oxide crystallites with oxygen, which leads to the formation of surface donor centers on grain boundaries. With an increase in partial oxygen pressure aluminum is mainly oxidized by the oxygen from the gas atmosphere, forming an intrinsic barrier phase on grain boundaries.
The development and formation of X-ray crystallography of macromolecules, or protein crystallography, is one of the most important achievements of science in the 20th century. The possibility of establishing the three-dimensional structures of macromolecules of proteins and nucleic acids at atomic level has ensured the rapid development of molecular biology, biochemistry, bioengineering, and biotechnology and allowed researchers to reach the modern level of pharmacology. The review considers the results of studies of protein structures performed at the Shubnikov Institute of Crystallography of the Russian Academy of Sciences from the 1960s up to now.
The morphology and crystal structure of Au nanoparticles obtained by irradiating a solution of hydrochloroauric acid HAuCl4 with laser pulses have been investigated by transmission electron microscopy, electron diffraction, and electron tomography. Along with round and shapeless particles, characterized by a cubic structure with twins, there are flat particles with trigonal morphology. They have a layered microstructure, with alternation of face-centered cubic and close-packed hexagonal crystal structures of layers oriented parallel to the base prism planes.
The oligomeric state of the nucleoid-associated protein IHF (integration host factor) plays a significant role in the organization and compaction of the bacterial nucleoid and also in the evolution of bacterial resistance to unfavorable environmental conditions, in particular to antibiotics. Although IHF was identified more than 25 years ago, the molecular mechanisms of its participation in these processes are poorly understood. Using small-angle X-ray scattering, it was demonstrated for the first time that there are different oligomeric states of IHF in an aqueous medium depending on the presence of metal cations. It was found that the presence of Mg2+ and K+ ions hinders the formation of high-order oligomers of IHF. The results of this study may be useful in the development of strategies against bacterial resistance to drugs.
The latest studies of electrically induced photonic liquid crystal structures, performed at the Laboratory of Liquid Crystals of the Shubnikov Institute of Crystallography of the Russian Academy of Sciences, are reviewed. Due to the field-induced spatial modulation of the refractive index, these structure exhibit optical properties that are characteristic of photonic crystals. Two types of structures are discussed. The first is induced in cholesteric liquid crystals with spontaneous formation of a helical director distribution. The orientational transition to the state with a lying helix (i.e., axis lying in the layer plane) is considered. The second type includes homogeneous layers of nonchiral nematic liquid crystals, in which refractive index modulation is due to the effect of flexoelectric instability. In both cases the periodic boundary conditions for the molecular orientation are of fundamental importance. Both the methods for setting boundary conditions and the photonic properties of structures are considered.
The dynamics of the parameters of the diffraction peak 0012 of LiNbO3:Fe crystals was recorded with a time resolution of less than 1 ns using synchronization of nanosecond laser pulses with synchrotron bunches of the KISI-Kurchatov source. The impact of a laser pulse (λ = 532 nm, τ = 4 ns, energy density 0.6 J/cm2) at different polarization directions of laser radiation causes a change in the peak intensity; this change depends on the angle between the laser beam polarization direction and the crystallographic axes. The obtained results are supplemented with the wavelet analysis of experimental data. The observed polarization dependence correlates with the data in the literature on the photovoltaic effect.
Small-angle scattering (SAS) of X-rays and neutrons is a technique for studying the subatomic structure of condensed matter with a resolution of tenths to hundreds of nanometers, the capabilities of which have grown significantly in recent decades due to the emergence of bright synchrotron radiation sources and laboratory facilities with microfocus sources. The growth of computing power was accompanied by the development of new algorithms and techniques for data analysis, which made SAS one of the most effective methods for studying nanoscale structures. After a brief presentation of the basic principles of SAS for isotropic dispersed nanosystems, some of the most striking examples of such analysis are given: modeling the structure of biological macromolecules in solution, determining the size distributions of inhomogeneities in polydisperse systems, and studying multicomponent systems of nanoparticles of different nature. The SAS method does not require special sample preparation and allows studying objects under conditions close to natural ones, which is especially demanded in the development of nature-like technologies.
LiRF4 (R = Y, Yb, Lu) nanoparticles (NPs), co-doped by Yb3+/Er3+ and Yb3+/Tm3+ ions, have been synthesized by high-temperature coprecipitation method. The influence of the molar ratio of precursors and the cation composition of matrices on the sizes and morphology of particles is investigated. The method of heterogeneous crystallization of these compounds using LiYF4 nanoseeds is optimized, which opens opportunities to controlled synthesis of LiRF4 NPs with required characteristics. Among the objects studied, LiYF4@LiYbF4:Tm3+@LiYF4 NPs demonstrate the most intense anti-Stokes photoluminescence in the UV (λ = 362 nm) and blue (λ = 450 nm) ranges, which exceeds the corresponding characteristics for β-NaYF4:Yb3+/Tm3+@NaYF4 particles. LiYF4@LiLuF4:Yb3+/Er3+@LiYF4 NPs are the most efficient IR converters in the (λ = 1530 nm) among the investigated isostructural matrices; their spectral-luminescence characteristics are close to those of the β-NaYF4:Yb3+/Er3+@NaYF4 compound with the equivalent degree of codoping. The results obtained give possibilities to consider LiYF4@LiYbF4:Tm3+@LiYF4 and LiYF4@LiLuF4:Yb3+/Er3+@LiYF4 NPs as a real alternative to the most widely used phosphors based on hexa-gonal β-NaYF4 host for photonics and biotechnology applications.
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