Andrey S. Orekhov

Structural peculiarities of single crystal diamond needles of nanometer thickness

Diamond is attractive for various applications due to its unique mechanical and optical properties. In particular, single crystal diamond needles with high aspect ratios and sharp apexes of nanometer size are demanded for different types of optical sensors including optically sensing tip probes for scanning microscopy. This paper reports on electron microscopy and Raman spectroscopy characterization of the diamond needles having geometrically perfect pyramidal shapes with rectangular atomically flat bases with (001) crystallography orientation, 2-200 nm sharp apexes, and with lengths from about 10-160 μm. The needles were produced by selective oxidation of (001) textured polycrystalline diamond films grown by chemical vapor deposition. Here we study the types and distribution of defects inside and on the surface of the single crystal diamond needles. We show that sp3 type point defects are incorporated into the volume of the diamond crystal during growth, while the surface of the lateral facets is enriched by multiple extended defects. Nitrogen addition to the reaction mixture results in increase of the growth rate on {001} facets correlated with the rise in the concentration of sp3 type defects.

Migration and Proliferative Activity of Mesenchymal Stem Cells in 3D Polylactide Scaffolds Depends on Cell Seeding Technique and Collagen Modification

We analyzed viability of mesenchymal stem cells seeded by static and dynamic methods to highly porous fibrous 3D poly-L-lactide scaffolds with similar physical and chemical properties, but different spatial organization modified with collagen. Standard collagen coating promoted protein adsorption on the scaffold surface and improved adhesive properties of 100 μ-thick scaffolds. Modification of 600-μ scaffolds with collagen under pressure increased proliferative activity of mesenchymal stem cells seeded under static and dynamic (delivery of 100,000 cells in 10 ml medium in a perfusion system at a rate of 1 ml/min) conditions by 47 and 648%, respectively (measured after 120-h culturing by MTT test). Dynamic conditions provide more uniform distribution of collagen on scaffold fibers and promote cell penetration into 3D poly-L-lactide scaffolds with thickness >600 μ.

Single-Walled Carbon Nanotube Reactor for Redox Transformation of Mercury Dichloride

Single-walled carbon nanotubes (SWCNTs) possessing a confined inner space protected by chemically resistant shells are promising for delivery, storage, and desorption of various compounds, as well as carrying out specific reactions. Here, we show that SWCNTs interact with molten mercury dichloride (HgCl2) and guide its transformation into dimercury dichloride (Hg2Cl2) in the cavity. The chemical state of host SWCNTs remains almost unchanged except for a small p-doping from the guest Hg2Cl2 nanocrystals. The density functional theory calculations reveal that the encapsulated HgCl2 molecules become negatively charged and start interacting via chlorine bridges when local concentration increases. This reduces the bonding strength in HgCl2, which facilitates removal of chlorine, finally leading to formation of Hg2Cl2 species. The present work demonstrates that SWCNTs not only serve as a template for growing nanocrystals but also behave as an electron-transfer catalyst in the spatially confined redox reaction by donation of electron density for temporary use by the guests.

Electron microscopy characterization of higher manganese silicide film structure on silicon

The structure and composition of higher manganese silicide (HMS) films on Si(111) substrate are studied by high-resolution transmission electron microscopy, electron diffraction, and energy-dispersive X-ray spectroscopy. The formation of Mn4Si7 HMS film by the deposition of the gas-phase manganese onto silicon at 1040°C is observed. The film/substrate interface is semicoherent and does not contain any intermediate layer. The interface structure is refined by computer simulation. The orientation relationship

Effect of a quasicrystalline filler on the tribological properties of a composite based on ultrahigh-molecular-weight polyethylene

\left( {\overline 1 \overline 2 4} \right)\left[ {443} \right]M{n_4}S{i_7}||\left( {1\overline 1 \overline 1 } \right)\left[ {001} \right]Si

Evaluation properties of bioelectrodes based on carbon superfine materials containing model microorganisms Gluconobacter

(1¯2¯4)[443]Mn4Si7||(11¯1¯)[001]Si between the film and substrate is determined.

Electrospinning of Nonwoven Fabrics from Polypropylene Melt with Additions of Stearates of Divalent Metals

In this article, we present a comparative study of field emission (FE) properties of the films of pristine, annealed and CuCl-filled single-walled carbon nanotubes (SWCNTs). The current-voltage dependencies and emission site distributions were measured in the diode configuration with a flat phosphor-coated anode. A significant increase of the threshold field was observed after annealing and doping of the films. It was explained by the selective oxidation of the small-diameter nanotubes confirmed by the Raman spectroscopy. The FE properties of annealed and filled SWCNTs were found to coincide with each other. At the same time, their Raman spectra differ significantly indicating the strong p-type doping induced by encapsulated CuCl. The obtained result reveals that the CuCl filling leads to significant changes in macroscopically averaged electronic properties but do not change the local work function at the apexes of emitting nanotubes, which is important for the further development of SWCNTs-based FE cathodes.

The Study of Nb3Sn Phase Content and Structure Dependence on the Way of Ti Doping in Superconductors Produced by Bronze Route

We prepare composites in which ultrahigh-molecular-weight polyethylene (UHMWPE) is used as a matrix and quasicrystalline Al–Cu–Fe powder is used as a filler with concentrations of 1, 10, 30, and 50 vol %. The mechanical and tribological properties of the samples are measured, and electron microscopic studies of fractured regions are performed. It is shown that with increasing concentrations of the filler, the nature of fracturing of the samples changes. The minimum value of the friction coefficient is 0.07. It is assumed that the limiting factor in improving the tribological properties of UHMWPE–quasicrystal composites is the chipping of filler particles from the polymer matrix.