Growth and characterisation of BNC nanostructures

BNC nanostructures were produced by the resistive heating of graphite and boric acid powder in a high isostatic pressure apparatus at a temperature of ∼1650 °C, with a nitrogen pressure of 12 MPa. The resultant nanostructures were examined using transmission electron microscopy, electron energy-loss spectroscopy and X-ray photoelectron spectroscopy. The growth mechanisms of the nanostructures are discussed.     

Nanostructured Ti-Cr-B-N and Ti-Cr-Si-C-N coatings for hard-alloy cutting tools

Nanostructured Ti-Cr-B-N and Ti-Cr-Si-C-N coatings with various contents of chromium and nitrogen are obtained by the magnetron sputtering of multiphase composite targets. Their structure and phase composition are investigated by X-ray phase analysis, transmission and scanning electron microscopy, X-ray photoelectron spectroscopy, and optical emission glow-discharge spectroscopy. The Ti-Cr-B-N and Ti-Cr-Si-C-N coatings are based on the fcc phase with texture (100) and crystallite size <25 nm. The Si₃N₄-based hexagonal phase was also revealed in the Ti-Cr-Si-C-N coatings. An investigation into the properties of coatings with the use of methods of nanoindentation, scratch testing, and by performing tribological tests showed that they have a hardness of up to 30 GPa, an adhesion strength no lower than 35 N, and their friction coefficient falls in the range of 0.35–0.57. Coatings also possess high thermal stability, resistance to oxidation, and corrosion stability in a 1N H₂SO₄ solution. The data obtained in tests of hard-alloy cutting tools indicate that the deposition of nanostructured Ti-Cr-B-N and Ti-Cr-Si-C-N coatings increases its resistance by a factor of 11–17.     

Chemical and phase composition of nanosized oxide and passive films on Ni-Cr alloys. II. XPS analysis of films produced by anodic passivation of alloys in 1 N H<Subscript>2</Subscript>SO<Subscript>4</Subscript>

XPS data of thin (1 to 2 nm) oxide films formed by the anodic passivation of Ni-2 at % Cr and Ni-6 at % Cr alloys in 1 N H₂SO₄ are discussed. Thermodynamic calculations of the solid-phase chemical reaction 3NiO + 2Cr = Cr₂O₃ + 3Ni are carried out taking into account the changes in the surface energy at the alloy-oxide film interface along with the Gibbs energy change in the alloy oxidation reaction.     

Composition and microstructure of the luminescence-active area in the light-emitting SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>(Si) nanocomposite layers

Features of formation, the composition, and the mictostructure of the luminescence-active transition region arising in the course of the deposition of the SiO _x N _y (Si) nanocomposite layer with the use of the reactive ion sputtering of the Si target in the O₂ and N₂ atmosphere are studied. The composition and the microstructure of the transition regions are analyzed using the methods of the X-ray photoelectron spectroscopy (XPS) upon the layer-by-layer etching of the composite layers. it is found that the transition regions contain amorphous clusters and nanocrystals of Si as well as such nanoinclusions as Si-Si chains in the oxynitride matrix. The influence of the microstructure on the characteristics of the electroluminescence of nanocomposite layers is revealed.     

Chemical and phase composition of nanosize oxide and passive films on Ni-Cr alloys. I. XPS studies of films obtained by alloy oxidation in air

XPS data for thin (less than 100 nm) oxide films obtained by oxidation of Ni-4 Cr and Ni-12.5 Cr alloys at 500°C (0.5 h) are discussed. Thermodynamic analysis of 3 NiO + 2 Cr = Cr₂O₃ + 3 Ni solid-phase reaction is given, in which both the Gibbs energy change in the thermochemical process and the change in the interface energy at the alloy-oxide film boundary are taken into account.     

Optical properties,defects, and composition of La<Subscript>3</Subscript>Ga<Subscript>5.5</Subscript>Ta<Subscript>0.5</Subscript>O<Subscript>14</Subscript> crystals

La₃Ga_5.5Ta_0.5O₁₄ crystals were grown in pure argon and in an argon + 2% oxygen atmosphere. The growth atmosphere significantly effects the elemental composition of the crystals, their color, and the genesis and intensity of absorption bands in the ultraviolet, visible, and infrared spectral regions. Two types of defects were identified in the crystals: planar interstitial defects and nearly spherical vacancy-type defects.     

Spectroscopic and first-principles studies of boron-doped diamond: Raman polarizability and local vibrational bands

Using the first-principles study within the local-density approximation, the projector augmented wave method and plane-wave basis, calculating the Hellmann–Feynman forces and applying the direct method for lattice-dynamical analysis, the relaxation of the structures and partial density of phonon states in boron-doped diamond crystals of BC₇, BC₃₁, BC₆₃ and BC₂₁₅ were obtained. It is found that lattice parameters, as well as the B–C and C–C bondlengths, increase with doping, at that the B–C bond is longer than the C–C bond even in the BC₂₁₅ crystal with smaller concentration of boron (0.46%). The comparison of partial densities of phonon states for boron and carbon atoms, as well as for carbon in undoped diamond, shows that localized vibrations of boron atoms contributes to the density of phonon states and Raman spectra of B-doped diamond.     

Nature and spatial localization of electroluminescence sources in the metal-composite layer-semiconductor structures

Variations in the electroluminescence spectra and intensity of the metal-composite layer-semiconductor (Au-SiO _x N _y (Si)-cSi) structures as functions of the characteristics of the luminescent-active transition region at the interface of the cSi substrate and the SiO _x N _y (Si) composite layer are studied. New information on localization of the electroluminescence sources in the transition region is obtained. It is found that the transition region contains various luminescence-active silicon inclusions, which contribute to both the short-wavelength (λ ≈ 500–1000 nm) and long-wavelength (λ ≈ 1000–1600 nm) branches of electroluminescence. The effect of technological factors on the electroluminescence spectra, intensity, and quantum efficiency is analyzed.     

Properties of nanosilicon obtained by plasma chemical decomposition of monosilane in a microwave discharge

Investigations of nanoscale silicon powders obtained by plasma chemical synthesis in various process parameters were carried out by transmission electron microscopy, X-ray photoelectron spectroscopy, and infrared (IR) spectroscopy. It was demonstrated that the powders consist of spherical particles with an average diameter from 20 to 30 nm. Each particle includes a single-crystal silicon core and amorphous shell whose chemical composition is defined by bonds of silicon with oxygen and hydrogen. The measurements of photoluminescence (FL) show the presence of dim near-infrared FL in the specimen powders, and more intensive emission around 420 nm in the suspension of the powder in ethanol. The character of this emission has not been determined yet.