Alkoxide Route to Re- and Mo-Based Metallic and Oxide Materials

The oxomethoxo complexes Re₄O₂(OMe)₁₆, Re₄O₆(OMe)₁₂, and Re_{4 –x} Mo _x O₆(OMe)₁₂ (x = 0.10, 2.82) are prepared via anodic dissolution of rhenium and molybdenum in methanol in the presence of LiCl. The phase composition of the solid products obtained by decomposing the synthesized complexes in oxidizing, inert, and reducing atmospheres is examined by x-ray diffraction. The results demonstrate that, by decomposing these complexes in the range 150–500°C, one can obtain Re-based metallic and oxide materials: ReO₃, monoclinic ReO₂, orthorhombic (Re,Mo)O₂ solid solutions, metallic Re powder, and Re–Mo alloys, including nanocrystalline powders.     

A comparative analysis of the design features of solar collectors made in Russia and abroad. New technical solutions

We present a comparative analysis of the thermal-engineering parameters and design features of solar collectors made in Russia and abroad. Substantiated proposals are given for using in them new structural materials (plastics resistant to high temperatures and ultraviolet radiation).     

Spectroscopy of Single AlInAs Quantum Dots

A system of quantum dots based on Al _x In_1?xAs/Al _y Ga_1?yAs solid solutions is investigated. The use of Al _x In_1?xAs wide-gap solid solutions as the basis of quantum dots substantially extends the spectral emission range to the short-wavelength region, including the wavelength region near 770 nm, which is of interest for the development of aerospace systems of quantum cryptography. The optical characteristics of Al _x In_1?xAs single quantum dots grown by the Stranski–Krastanov mechanism were studied by cryogenic microphotoluminescence. The statistics of the emission of single quantum dot excitons was studied using a Hanbury Brown–Twiss interferometer. The pair photon correlation function indicates the sub-Poissonian nature of the emission statistics, which directly confirms the possibility of developing single-photon emitters based on Al _x In_1?xAs quantum dots. The fine structure of quantum dot exciton states was investigated at wavelengths near 770 nm. The splitting of the exciton states is found to be similar to the natural width of exciton lines, which is of great interest for the development of entangled photon pair emitters based on Al _x In_1?xAs quantum dots.     

Production technology for ladle brick using semiacid clays

Conclusions A technology was developed for making ladle brick from Ch1PK semiacid clays mined in the Chasov Yar area.The biggest difference between semiacid ladle brick and firebrick is the after-expansion at service temperatures of 1500–1600° C which reaches about 3% and which densifies the structure of the ladle.The life of semiacid brick in 250-ton steel ladles on average is 11% higher than ordinary ladle brick.The production of ladle brick from semiacid raw materials is economic. The lower cost of the product is a result of using cheaper raw materials and firing the clay into chamotte and products at lower temperatures.Translated from Ogneupory, No. 5, pp. 3–7, May 1967.     

Chloride vapor-phase epitaxy of gallium nitride on silicon: Structural and luminescent characteristics of epilayers

The structure and luminescent properties of gallium nitride (GaN) epilayers grown by hydride-chloride vapor-phase epitaxy (HVPE) in a hydrogen or argon atmosphere on 2-inch Si(111) substrates with AlN buffer layers have been studied. The replacement of hydrogen atmosphere by argon for the HVPE growth of GaN leads to a decrease in the epilayer surface roughness. The ratio of intensities of the donor-acceptor and exciton bands in the luminescence spectrum decreases with decreasing growth temperature. For the best samples of GaN epilayers, the halfwidth (FWHM) of the X-ray rocking curve for the (0002) reflection was 420 sec of arc, and the FWHM of the band of exciton emission at 77 K was 48 meV.     

Heteropolytype structures with SiC quantum dots

Epitaxial silicon carbide layers of 3C-SiC polytype with an array of nanodimensional SiC quantum dots (QDs) have been obtained for the first time using an improved method of sublimation epitaxy in vacuum. The X-ray topography and X-ray diffraction data unambiguously confirm the formation of a 3C-SiC epilayer with twinned regions on the surface of a 6H-SiC substrate. The surface topography of epilayers was studied by atomic force microscopy (AFM), and the microstructure of a near-surface layer of the deposit was investigated by transmission electron microscopy (TEM). Using the AFM and TEM data, the presence of QDs (representing SiC nanoislands) is established, and their average dimensions and concentration are evaluated.     

Investigation of impact of solid particles against hardmetal and cermet targets

The objective of the present work is to investigate and discuss some features of the surface damage and material removal process during particle-wall collision of the solid particles and hardmetal and cermet targets. The restitution parameters of TiC-base cermets, WC–Co hardmetals and glass of different composition and properties have been investigated. In order to clarify the details of the impact of glass spheres and corundum particles of irregular shape on a solid half-space, the process of interaction of solid particle with target was studied using a Laser Doppler Anemometer (LDA) measuring technique. Targets were impacted with particles over the range of impact velocities (7–50 m s⁻¹) at impact angle 67°. The experimentally observed variations of the coefficient of velocity restitution as a function of the test material properties, impact velocity and hardness ratio (H_m/H_a) are adequately explained on the basis of a theoretical model. Systematic studies of the influence of the impact variables on the collision process have been carried out.     

Structural defects and deep-level centers in 4H-SiC epilayers grown by sublimational epitaxy in vacuum

The parameters of deep-level centers in lightly doped 4H-SiC epilayers grown by sublimational epitaxy and CVD were investigated. Two deep-level centers with activation energies E _c -0.18 eV and E _c -0.65 eV (Z1 center) were observed and tentatively identified with structural defects of the SiC crystal lattice. The Z1 center concentration is shown to fall with decreasing uncompensated donor concentration N _d -N _a in the layers. For the same N _d -N _a , the Z1 center concentration is lower in layers with a higher dislocation density.