Modification of germanium nanoclusters in GeO x films during isochronous furnace and pulse laser annealing

We have studied the formation and modification of germanium nanoclusters in GeO _x films under the action of pulse laser and isochronous furnace annealing. Pulse treatments were effected using either a Tisapphire laser operating at a wavelength of λ = 800 nm and a pulse duration τ of about 30 fs or a KrF excimer laser with λ = 248 nm and τ = 25 ns. The pulse annealing stimulated both the crystallization of initial amorphous Ge nanoclusters in GeO _x matrix and the formation of new nanoclusters. In order to prevent the evaporation of films under the action of laser radiation, the samples were covered with a protective layer of SiN _x O _y . The proposed approach can be used for the modification of dimensions and phase composition of Ge clusters in GeO _x films.     

Application of particle tracking velocimetry for studying the dispersion of particles in a turbulent gas flow

A method for the determination of the dispersion of solid particles in a turbulent gas flow has been presented. This method is based on recording the particle trajectories with a high-speed video camera on separate regions of a flow, located at various distances from a point source of particles, and the subsequent processing of the frames. This method has been used to study the dispersion of solid particles under the conditions of turbulence in a horizontal channel with a rectangular cross section of 200 × 400 mm for a measuring region length of 2 m. Turbulence of the gas flow was generated by means of a grid with square meshes of the size of 16 mm. The average velocity of the gas flow in the measuring region was 5.1 m/s. The dispersion of 36-, 56- and 128-micron glass particles of spherical shape was studied in a region 450 mm long from the point source of particles. It has been shown that the dispersion of these particles in the direction of the action of the gravity force is larger than their dispersion in the perpendicular direction to the gravity force. The results of this study have shown that an increase in the size of particles leads to a decrease in the dispersion at small flight times of the particles (short-time dispersion).     

Nondestructive Evaluation of Changes in Local Density of Compressed Components from Composite Materials

The paper analyzes improvements in the gamma-method for nondestructive evaluation of density of constant-thickness components fabricated from highly filled composite materials. A facility designed for such measurements is described. The parameters of the radiation source and detecting instrument required to guarantee the high precision of the method are determined. Results of tests of the experimental facility are given.     

Bulk GaN layers grown on oxidized silicon by vapor-phase epitaxy in a hydride-chloride system

Bulk GaN layers with a thickness of up to 1.5 mm and a lateral size of 50 mm were grown by hydride-chloride vapor-phase epitaxy (HVPE). The best samples show a half-width (FWHM) of the X-ray rocking curve of ω_θ=27′, a charge carrier density of ∼8 × 10¹⁹ cm⁻³, and a mobility of ∼50 cm²/(V s). The photoluminescence spectra of the obtained epitaxial GaN layers exhibit an edge emission band at 348 eV. The HVPE layers are characterized by a high mechanical strength: H _V = 14 GPa.     

A study of n +-6H/n-3C/p +-6H-SiC heterostructures grown by sublimation epitaxy

The n ⁺-6H/n-3C/p ⁺-6H-SiC structure was fabricated for the first time by sublimation epitaxy, with mesa diodes formed on its base and their electrical characteristics were studied. It was found that a green band dominates in the spectrum of injection electroluminescence (EL) of these diodes. The band is close by its parameters to that associated with free-exciton recombination in bulk 3C-SiC, but is shifted by ～0.06 eV to shorter wavelengths. A similar effect was observed previously for triangular quantum wells in an n ⁺-6H-SiC/p-3C-SiC heterojunction. An analysis of the experimental data obtained demonstrated that the structure can be regarded as two independent heterojunctions. The EL spectrum observed may be associated with radiative recombination at the n ⁺-6H-SiC/n-3C-SiC heterointerface.     

Nanomaterials based on group III–VII rare elements: Targeted synthesis,structure, and properties

We systematize the results of studies aimed at creating physicochemical principles of the fabrication of metallic and oxide nanomaterials based on rare elements (Nb, Ta, Re, Mo, W, and rare-earth elements). The key point of the approach under development is the preparation of metallic (metals and alloys) and oxide (binary and mixed oxides) powders via the thermal decomposition of mono-and polymetallic hydroxy and oxyalkoxy derivatives. We describe the preparation and characterization of nanopowders of refractory metals, alloys, oxides, and their solid solutions with controlled properties.     

Computational investigation of the temperature and geometric characteristics of VVÉR fuel in the Kozlodui nuclear power plant (Bulgaria) under normal operating conditions

A method of performing stationary thermomechanical calculations of VVéR-440 and-1000 fuel elements, using the TRANSURANUS computer code to obtain the dependence of the temperature and radius of the fuel elements on the lineal power ensity and burnup, is described. These dependences are intended for use in neutron-physical calculations of the VVéR reactor at the Kozlodui nuclear power plant in stationary and transient regimes. The results obtained with this computer program are compared with calculations performed using the certified TOPRA-s code. The comparison shows reasonable agreement between the results of calculations of the fuel temperature. __________ Translated from Atomnaya énergiya, Vol. 101, No. 5, pp. 336–342, November, 2006.     

The energy characteristics of wave propagation through interfaces of media with complex parameters

With the use of the 1D wave equation as an example, the wave incidence on one interface and on two interfaces of media with arbitrary complex parameters is analyzed. It is noted that, when the energy reflection, transmission, and absorption coefficients are calculated by means of traditional techniques, their sum exceeds unity if the wave number in the first medium is complex. The complex character of the energy balance on the media interfaces is revealed. Definitions are introduced and the properties of complex reflection, transmission, localization, reactivity, and absorption are considered.     

Dispersion of magnetostatic waves in a tangentially magnetized ferrite wafer with normal uniaxial anisotropy

A dispersion law is obtained and analyzed for the first time for magnetostatic waves in a tangentially magnetized ferrite wafer with uniaxial anisotropy where the axis is perpendicular to the plane of the wafer and the applied static magnetic field is weaker than the anisotropy field. This model qualitatively describes the dispersion of magnetostatic waves in hexa-and orthoferrite wafers and also in an unsaturated ferrite wafer. Pis’ma Zh. Tekh. Fiz. 25, 73–78 (November 26, 1999)