[show abstract][hide abstract] ABSTRACT: The structure of PSZ crystals have been studied in relation to the content of the stabilizing impurity
(Y2O3) by X-ray diffraction and transmission electron microscopy. The measurement of both hardness
and fracture toughness by microindentation have been carried out. Studies have shown that crystals of
PSZ obtained by directional solidification of the melt consist of two tetragonal phases (t and t’), with varying
degrees of tetragonality. The yttrium-enriched phase t’ is ‘‘untransformable’’ in contrast to the t phase,
with a lower content of yttrium, which, under the influence of mechanical stress, undergoes a martensitic
transition to the monoclinic form. Increasing the stabilizing impurity concentration leads to an increase
in the volume fraction of the ‘‘untransformable’’ phase. Increasing the concentration of Y2O3 also affects
the form and dispersion of the twin domains. The character of the twinned structure changes depending
on the concentration of the stabilizing impurity and the hierarchy of the twinning disappears above
3 mol.% Y2O3. In this work it is shown that the quantity of hardening (fracture toughness) is proportional
to the content of the transformable t phase.
Journal of Alloys and Compounds 01/2014; 586(Supplement 1):S231–S235. · 2.39 Impact Factor
[show abstract][hide abstract] ABSTRACT: Some results on the creation of ultraviolet light-emitting diodes based on GaN/AlGaN heterostructures grown on aluminum nitride (AlN) substrates using the method of chloride-hydride epitaxy are presented. The peak wavelengths lie within the range of 360–365 nm, the width of a spectral curve is 10–13 nm, and the output optical power of light-emitting diode chips is 50 mW at a current of 350 mA.
[show abstract][hide abstract] ABSTRACT: The dependence of the thermoelectric properties of the nanostructured bulk (Bi,Sb)2Te3 material on the composition and the spark plasma-sintering (SPS) temperature T
SPS has been studied. It has been revealed that the Bi0.4Sb1.6Te3 solid solution sintered at a temperature of 450–500°C has a thermoelectric figure of merit ZT = 1.25–1.28. The dependence of thermoelectric properties on the sintering temperature T
SPS above 400°C is correlated to the transformation of the fine structure of the material due to the rearrangement of point vacancy-donor defects in the process of repeated recrystallization. It has been established that point structural defects make a considerable contribution to the formation of the thermoelectric properties of nanostructured material.
[show abstract][hide abstract] ABSTRACT: A comparative analysis of structures of compact samples of Bi0.5Sb1.5Te3 thermoelectric materials, obtained by the spark plasma sintering (SPS) and traditional hot-pressing methods, was performed by the X-ray diffractometry and scanning electron microscopy methods. It is shown that the spark plasma sintering method failed to obtain structure sizes smaller than the hot-pressing method. However, the sintering quality, characterized by the absence of pores and cracks, and sizes of fragments of the fractured surface, is higher at comparable temperatures in the samples obtained by the SPS-method.
[show abstract][hide abstract] ABSTRACT: A nanopowder from p-Bi-Sb-Te with particles ~ 10 nm were fabricated by the
ball milling using different technological modes. Cold and hot pressing at
different conditions and also SPS process were used for consolidation of the
powder into a bulk nanostructure and nanocomposites. The main factors allowing
slowing-down of the growth of nanograins as a result of recrystallization are
the reduction of the temperature and of the duration of the pressing, the
increase of the pressure, as well as addition of small value additives (like
MoS2, thermally expanded graphite or fullerenes). It was reached the
thermoelectric figure of merit ZT=1.22 (at 360 K) in the bulk nanostructure
Bi0,4Sb1,6Te3 fabricated by SPS method. Some mechanisms of the improvement of
the thermoelectric efficiency in bulk nanocrystalline semiconductors based on
BixSb2-xTe3 are studied theoretically. The reduction of nanograin size can lead
to improvement of the thermoelectric figure of merit. The theoretical
dependence of the electric and heat conductivities and the thermoelectric power
as the function of nanograins size in BixSb2-xTe3 bulk nanostructure are quite
accurately correlates with the experimental data.
[show abstract][hide abstract] ABSTRACT: This paper presents the analysis of peculiarities of defect formation in the course of thermal treatment in silicon single crystals grown by the Czochralski method and exposed to thermal-neutron radiation, under the modes usually applied in transmutation doping of silicon ingots. The processes of defect formation were estimated using X-ray diffuse scattering and IR-spectroscopy. It is demonstrated that such doping results in the variation of the state in the material lattice of impurities such as oxygen and carbon. Moreover, subsequent high-temperature annealing leads to the recovery of concentration of interstitial oxygen and does not result in the recovery of the carbon concentration in the lattice nodes. The effect is studied of radiation on peculiar features of the formation of oxygen-containing microdefects in a silicon lattice at high-temperature annealing, used for the formation of an internal getter in silicon wafers.
[show abstract][hide abstract] ABSTRACT: The structural characteristics and electrical properties of bulk aluminum nitride crystals grown by sublimation and used as substrates for light emitting diode (LED) structures and AlGaN/GaN field effect transistors were studied. The crystalline perfection was assessed by selective chemical etching and by X-ray diffraction techniques. Electrical and optical properties were investigated using the temperature dependence of conductivity, admittance spectroscopy, high-temperature/low-frequency capacitance voltage measurements and by photoinduced transient current spectroscopy (PICTS), microcathodoluminescence (MCL) spectra and MCL imaging techniques. It was established that the studied samples were single crystals with a large grain substructure, with characteristic grain size of several hundred microns and a dislocation density of 102–104 cm−2 inside the grains. The electrical characteristics of the crystals were governed by the compensation of residual donors with a level near E
c—0.3 eV by deep centers with activation energy of 0.7 eV, both centers manifesting themselves in the temperature dependence of conductivity and in admittance spectra. In addition, deep centers responsible for the luminescence band with the peak energy of 3.3 eV and associated with low-angle grain boundaries were also observed.
[show abstract][hide abstract] ABSTRACT: Specific features of formation of radiation defects in thin silicon layer of silicon-on-insulator (SOI) structures have been
studied. It is shown that there are differences between variations in the structural and electrical properties of the thin
silicon layer and those in bulk silicon crystals (with similar electrical characteristics) subjected to the same radiation
effect. It is established that the embedded insulator in the SOI structure represents a barrier for motion of radiation-induced
intrinsic interstitial silicon atoms, which brings about an increase in the dose of bombarding ions, which leads to the loss
of single-crystallinity of the silicon layer in a SOI structure. It is shown that γ-ray irradiation with doses unaffecting
the electrical conductivity of bulk silicon crystals appreciably affects the conductivity of the silicon layer in the SOI
structures. In addition, variation in the conductivity of silicon layer is related to variation in the density of surface
states at the interface between the silicon layer and the built-in insulator, rather than to generation of conventional radiation-induced
structural defects in silicon.
[show abstract][hide abstract] ABSTRACT: In this work, we used x-ray structural diagnostic data to reveal the formation of structural regularities in profiled polycrystalline ingots based on Bi and Sb chalcogenide solid solutions. In Bi2Te3 lattice crystals, the solid phase grows such that the cleavage surfaces are perpendicular to the crystallization front. The crystallization singularity determines the nature of the growth texture. Because texture is an important factor determining the anisotropy of properties, which in turn determines the suitability of an ingot for production of modules and the possibility of figure of merit improvement, its diagnostics is an important issue for technology testing. Examples of texture analysis using the method of straight pole figure (SPF) construction for profiled crystals are provided. The structure of the surface layers in the profiled ingots was studied after electroerosion cutting. In addition, the method of estimation of the disturbed layer depth based on the nature of texture changes was used.
Journal of Electronic Materials 01/2011; 40(5). · 1.64 Impact Factor
[show abstract][hide abstract] ABSTRACT: Zirconia single crystals doped with 2.8, 3.2, 3.7, and 4.0 mol % of Y2O3 have been studied. The phase composition and structure have been studied by X-ray diffraction analysis and transmission electron
microscopy. It has been established that all investigated samples has two ZrO2 tetragonal phases with tetragonality c/a = 1.006–1.007 and c/a = 1.014–1.015 independent of the stabilizing impurity content. The former phase is not transformed, whereas the latter is
transformed into a monoclinic one. In all cases the samples have a developed twin structure. Twinning hierarchy is observed:
there are first-, second-, third-order, etc., twins, each of them containing the next-order twins inside them. Elastic stress
relaxation occurs by twinning rather than by generation of dislocations. The stabilizing impurity content affects the structure
nonmonotonically; the minimum dimensions of the twin lamellas refer to the Y2O3 concentration of 3.2 mol %.
Journal of Surface Investigation X-ray Synchrotron and Neutron Techniques 01/2011; 5(1):166-171. · 0.36 Impact Factor
[show abstract][hide abstract] ABSTRACT: Bulk nanostructured polycrystals are prospective thermoelectrics. Fabrication and examination of nanostructured polycrystalline
p-Bi-Sb-Te are discussed. The influence of fabrication conditions and the composition of the material on sizes of nanograins
was investigated experimentally. Basic physical properties of fabricated nanothermoelectrics including nanocomposites were
also studied. Theoretical estimation of the influence of phonon scattering on nanograin boundaries in bulk nanostructured
thermoelectrics is presented.
Journal of Electronic Materials 01/2010; 39(9):1650-1653. · 1.64 Impact Factor
[show abstract][hide abstract] ABSTRACT: The structure and the electrical and magnetic properties of Mn-implanted Si, which exhibits ferromagnetic ordering at room
temperature, are studied. Single-crystal n- and p-type Si wafers with high and low electrical resistivities are implanted by manganese ions to a dose of 5 × 1016 cm−2. After implantation and subsequent vacuum annealing at 850°C, the implanted samples are examined by various methods. The
Mn impurity that exhibits an electric activity and is incorporated into the Si lattice in interstitial sites is found to account
for only a few percent of the total Mn content. The main part of Mn is fixed in Mn15Si26 nanoprecipitates in the Si matrix. The magnetization of implanted Si is found to be independent of the electrical resistivity
and the conductivity type of silicon and the type of implanted impurity. The magnetization of implanted Si increases slightly
upon short-term postimplantation annealing and disappears completely upon vacuum annealing at 1000°C for 5 h. The Mn impurity
in Si is shown to have no significant magnetic moment at room temperature. These results indicate that the room temperature
ferromagnetism in Mn-implanted Si is likely to be caused by implantation-induced defects in the silicon lattice rather than
by a Mn impurity.
Journal of Experimental and Theoretical Physics 04/2009; 109(4):602-608. · 0.92 Impact Factor
[show abstract][hide abstract] ABSTRACT: Structural and electrical properties of nonpolar m -GaN films grown on m -SiC using standard metalorganic chemical vapor deposition (MOCVD) and two versions of sidewall epitaxial lateral overgrowth were studied. It is shown that lateral overgrowth allows one to dramatically reduce the dislocation density from over 10<sup>9</sup> cm <sup>-2</sup> to ∼10<sup>7</sup> cm <sup>-2</sup> . In good correlation with that we observed a strong reduction in the density of electron traps E<sub>c</sub>-0.25 eV and E<sub>c</sub>-0.6 eV from over 10<sup>15</sup> cm <sup>-3</sup> to ∼10<sup>14</sup> cm <sup>-3</sup> , respectively, in MOCVD m -GaN and in laterally overgrown m -GaN . Preliminary studies of the effects of changing the V/III ratio and of Si doping were performed. The MOCVD m -GaN films grown with high V/III ratio of 1000 were semi-insulating, with the Fermi level pinned near the 0.6 eV traps. Decreasing the V/III value to 250 shifted the Fermi level upward, close to the level of the 0.25 eV traps. Si doping in laterally overgrown samples strongly suppressed the formation of major electron traps but enhanced the formation of hole traps near E<sub>v</sub>+0.9 eV . We also report on electrical properties of the GaN interface with the AlN buffer used to facilitate good quality growth on SiC. These properties are dominated by a high concentration of 0.15 eV traps.
Journal of Applied Physics 04/2009; · 2.21 Impact Factor
[show abstract][hide abstract] ABSTRACT: The state of manganese impurity in implanted silicon at implantation doses of up to 5 × 1016 cm−2 has been investigated by X-ray diffraction and transmission electron microscopy. It is established that, after short-term
vacuum annealing at 850°C, most of the implanted manganese impurities are in microinclusions up to 20 nm in size formed by
a tetragonal silicide phase of the Mn15Si26 type.
[show abstract][hide abstract] ABSTRACT: The electrical and structural properties of AlN/GaN heterostructures grown by molecular beam epitaxy on sapphire are compared with those of AlGaN/GaN heterostructures. The structural characteristics as assessed by x-ray diffraction show little difference but the electron density in the two-dimensional electron gas is about twice higher for AlN/GaN structures with only slightly lower mobility than in AlGaN/GaN. By proper choice of the Fe doping in GaN(Fe) and the thickness of unintentionally doped GaN layers, the composite buffer of the structure can be made semi-insulating. The current through the AlN/GaN structures is determined by tunneling through the AlN barrier and is much higher than that for AlGaN/GaN films due to the lower thickness of AlN compared to AlGaN. Increasing the thickness of AlN from 3 to 4 nm decreases the leakage current by about an order of magnitude.
Journal of Applied Physics 10/2008; · 2.21 Impact Factor
[show abstract][hide abstract] ABSTRACT: The structure of manganese-implanted (dose 2 × 1016 cm−2) n-type and p-type silicon, ferromagnetic at room temperature, has been studied. During implantation, an amorphized layer is formed in
the silicon wafer. Subsequent vacuum annealing improves the structural quality of the implanted material and leads to the
formation of a vacancy solid solution of manganese in silicon. A difference in the degree of structural quality of silicon
implanted by different impurities has been experimentally established.
[show abstract][hide abstract] ABSTRACT: Microdefects in Si-doped GaAs single crystals grown by the vertical gradient freeze method have been studied with X-ray diffuse
scattering. In the case of doping to majority carrier concentrations n ∼ 1 × 1018 cm−3, large microdefects with positive dilatation that accompany the initial stage of arsenic precipitation at high temperatures
were observed. It is shown that GaAs samples heavily doped with silicon (n ∼ 3 × 1018 cm−3) contain large (several micrometers) interstitial microdefects, which can play the role of nucleation regions for new SiAs
and SiAs2 phases.
[show abstract][hide abstract] ABSTRACT: The thin films of zinc oxide have been produced at various levels of doping with gallium. The dependence of the ZnO film crystallographic parameters on the deposition process parameters has been established. The dependence of the photoluminescence spectra of films on the conditions of deposition has been investigated. A study has been made of the intensity, emission band width, and the value of Stokes shift of ZnO films.