Novel superconducting niobium beryllide Nb<Subscript>3</Subscript>Be with A15 structure

New niobium beryllide Nb₃Be with A15 structure and lattice parameter a=0.5187±0.0007 nm, coexisting (3–5%) with a tetragonal phase, presumably, of an ordered solid solution with parameters a=0.5414±0.0008 nm and c=0.6378±0.0009 nm, was synthesized by thermal treatment (875–110°C) of amorphous film coatings containing 26.8–32.4 at. % Be and formed from short-period Nb and Be layers by magnetron sputtering. The domain of existence of the Nb₃Be phase and the critical superconducting transition temperature (10.0 K and a transition width of 2.5 K) were determined and the X-ray structural data for structure identification were obtained.     

Imaging the elastic properties of coiled carbon nanotubes with atomic force microscopy

Coiled carbon nanotubes were produced catalytically by thermal decomposition of hydrocarbon gas. After deposition on a silicon substrate, the three-dimensional structure of the helix-shaped multiwalled nanotubes can be visualized with atomic force microscopy. Helical structures of both chiralities are present in the nanotube deposits. For larger coil diameters ( >170 nm), force modulation microscopy allows one to probe the local elasticity along the length of the coil. Our results agree with the classical theory of elasticity. Similar to the case of straight nanotubes, the Young modulus of coiled multiwalled nanotubes remains comparable to the very high Young modulus of hexagonal graphene sheets.     

Composite Materials with 2D Graphene Structures: Applications for Hydrogen Energetics and Catalysis with Hydrogen Participation

The work presents the results of studies concerning preparation of graphene-like nanomaterials by graphite oxide reduction, preparation of nickel-graphene catalysts, magnesium-graphene, and carbon-graphene composites. Optimum conditions for preparing these materials and their functional characteristics are determined.     

Electron-phonon interaction in boron-doped silicon nanocrystals: Effect of Fano interference on the Raman spectrum

Raman spectroscopy is employed for studying silicon nanocrystal arrays in boron-doped amorphous silicon films. The nanocrystals were formed in the initial amorphous films by the pulsed impact of an excimer laser. The electron-phonon interaction effects are observed experimentally in the heterostructure formed by a silicon nanocrystal and an amorphous matrix. These effects can be described in the framework of the familiar Fano interference model.     

Convergence of series of dependent φ-subgaussian random variables

The almost sure convergence of weighted sums of φ-subgaussian m-acceptable random variables is investigated. As corollaries, the main results are applied to the case of negatively dependent and m-dependent subgaussian random variables. Finally, an application to random Fourier series is presented.     

Raman scattering spectroscopy of inclusions of carbon in Al<Subscript>2</Subscript>O<Subscript>3</Subscript> films and its solid solutions with HfO<Subscript>2</Subscript>

We apply Raman scattering spectroscopy to study the nature of carbon inclusions in Al₂O₃ and (HfO₂) _x (Al₂O₃)_{1 ? x} films deposited using volatile complex compounds. Raman spectra of the films under investigation contain D and G vibrational modes, which indicate that carbon clusters of the sp ² configuration tend to form in the films. We estimate the size of clusters from the integrated intensity ratio I _D /I _G and find it to be in the range of 14–20 Å. The content of hydrogen in carbon clusters is calculated from the height of the photoluminescence pedestal and is found to vary from 14 to 30 at % depending on the regime of the film’s synthesis.     

Ferromagnetic resonance and bistability field in a uniaxial magnetic film

Peculiarities of ferromagnetic resonance (FMR) corresponding to bias along the “hard” magnetic axis of a film with 2D uniaxial anisotropy are studied based on numerical solution of magnetic moment dynamics equations. It is shown that an additional resonance peak is formed in the FMR spectrum in the vicinity of “bistability field” H _b . The dependence of this field on the amplitude of the microwave field and damping parameters is analyzed.     

Electrochemical activity of rhodium complexes supported on fibrous-carbon material

The redox properties of heterogenized Rh^I, Rh^II, and Rh^III complexes with different, particularly organophosphorus, ligands were studied by cyclic voltammetry (CVA). The support is a carbon-paste electrode based on a fibrous-carbon material and activated carbon. The electrochemical reduction of Rh^III produces Rh metal, which further catalyzes hydrogen evolution. After the reduction of water-soluble binuclear Rh^II complexes, the CVA curves exhibit peaks of electrocatalytic hydrogen evolution and irreversible Rh^I→Rh^II oxidation. The Rh^II complexes with organophosphorus ligands are characterized only by the peak of Rh^I→Rh^II oxidation. After reduction, the Rh^I complexes behave as a pseudo-reverse Rh⁰/Rh^I pair. The electron-donating properties of the ligand determine the reversibility of the system. The degree of structurization of the carbon matrix and the presence of phosphorus(v) atoms in it affect the electrochemical activity of the Rh^II and Rh^I complexes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 908–914, May, 1999.     

Ecdysteroid acetates fromAjuga reptans

The compounds 20-hydroxyecdysone-22-acetate and viticosterone E (20-hydroxyecdysone-25-acetate) are observed for the first time inAjuga reptans L. growing at the northern limit of its range in a middle taiga subzone of European northeastern Russia. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 607–610, September–October, 1999.     

Synthesis of carbon nanofibers by catalytic pyrolysis of ethylene and methane on hydrides of intermetallic compounds of lanthanum with nickel

Carbon nanofibers were synthesized by the pyrolysis of ethylene and methane on hydrides of intermetallides LaNi_nH_x (n = 2, 3, 5; x = 0.1–4). The influence of parameters of the synthesis (temperature and the ratio of gases in an Ar: H₂: C₂H₄ (CH₄) mixture) on the structure of nanofibers thus formed was studied. Hydrides of nickel intermetallides are more efficient catalytic systems than metallic nickel. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2210–2214, October, 2005.