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1
Content available remote Solubility Limit of Ni in Cd_{1-x}Ni_{x}Te Crystals
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The Cd_{1-x}Ni_{x}Te crystals were grown by the Bridgman method. The investigated samples were cut from five different ingots with nominal contents of nickel varied from 0.005 to 0.05. The investigations were performed using X-ray powder diffraction method and energy dispersive and wavelength dispersive electron microprobe analysis. The samples were ałso examined in a scanning electron microscope. Examinations of wavelength dispersive electron microprobe analysis show that the actual contents of nickel differ from the nominal values. The solubility limit of nickel was determined to be x = 0.005. The precipitates of NiTe were found in samples of a greater content of nickel. Their dimensions were between 5 to 90 micrometers. X-ray powder diffraction measurements did not reveal any significant change of the lattice constant of investigated crystals in comparison with pure CdTe.
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Content available remote Structural Properties of Cd_{1-x}Mg_{x}Te and Cd_{1-x-y}Mg_{x}Mn_{y}Te Crystals
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Electron probe microanalysis and X-ray diffraction studies have been performed on samples of ternary Cd_{1-x}Mg_{x}Te (0.05 ≤ x ≤ 0.09) and quaternary Cd_{1-x-y}Mg_{x}Mn_{y}Te (0.025 ≤ x ≤ 0.4; 0.025 ≤ y ≤ 0.7) alloys. The investigated samples were cut from 24 different ingots grown by Bridgman method. Microprobe examinations have revealed significant differences between actual and nominal content of Mg along the longitudinal direction for both ternary and quaternary ingots. In contrast to Mg, for most Cd_{1-x-y}Mg_{x}Mn_{y}Te samples the actual Mn content was within ±5% of nominal content. The lattice constants have been determined by X-ray powder diffraction method. Whereas Cd_{1-x-y}Mg_{x}Mn_{y}Te samples exhibit only zinc blende crystal structure for the entire region of x and y investigated, the Cd_{1-x}Mg_{x}Te alloy has two different structures depending on Mg content; a zinc blende structure below x = 0.5 and a wurtzite structure above it. In both alloys the lattice constant decreases with increasing Mg content.
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Content available remote X-Ray Study of Synthetic Alunite
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Synthetic alunite was obtained by two different synthesis methods. Powder data obtained with a standard Bragg-Brentano geometry of two analyzed samples are reported for a broad angular range. The chemical analysis as well as the unit-cell dimensions indicate that the analyzed alunite is K and Al deficient and contains excess water. A need for high resolution diffraction experiments is expressed.
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High pressure - high temperature experiments for MnTe of NiAs type were performed using a synchrotron radiation as X-ray source and a cubic anvil X-ray diffraction press to produce nonambient sample environment. In the investigated range of pressure (0-67.5 kbar) on uploading and with following temperature rise from 296 to 1273 K (at 67.5 kbar), the structure type of MnTe is conserved. An earlier reported nonlinear behaviour of lattice-parameter c_{0} is not found in the present study. Possible reasons of this discrepancy are discussed. The value of bulk modulus and its pressure derivative were calculated from the pressure-volume dependence by fitting the Birch-Murnaghan equation.
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Content available remote MBE Growth of YbTe on GaAs(100) and BaF_{2}(111) Substrates
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The structural properties of MBE grown YbTe layers were investigated by X-ray diffraction methods and photoluminescence measurements. YbTe films were grown on the ZnTe and CdTe buffer layers crystallised on the GaAs(100) 2° off oriented substrates and on the BaF_{2}(100) substrates. In the case of GaAs substrates the two-dimensional growth mode of YbTe was observed on reflection high energy electron diffraction picture. Results of the X-ray rocking curve and photoluminescence excitation measurements indicate that the structural properties of YbTe films are comparable to the properties of the MBE grown ZnTe and CdTe layers on the GaAs(100) substrates. The measured values of the YbTe lattice constant parallel and perpendicular to the growth plane show that the 1 μm thick layers are partially strained. The full width at half maximum values of the X-ray rocking curves are the smallest (900 arc seconds) for the YbTe films crystallised on the 2 μm thick CdTe bucher layer grown on the GaAs(100) substrate. In the case of BaF_{2}(111) substrate the two-dimensional MBE growth mode of YbTe was not observed.
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Content available remote Interfacial Reactions between Thin Films of Zinc and (100)InP
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The effects of interaction between thin films of Zn and (100)InP were studied with secondary ion mass spectrometry, X-ray diffraction and trans­mission electron microscopy. Zn was found to penetrate the native oxide on InP surface during deposition and to form an ohmic contact when deposited on highly doped n-type InP. Heat treatment causes the formation of Zn_{3}P_{2} phase lattice matched to InP.
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Content available remote Investigation of Porous Zn Growth Mechanism during Zn Reactive Sputter Deposition
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Ar-O-Zn plasma discharges created during DC reactive magnetron sputtering of a Zn target and RF reactive magnetron sputtering of a ceramic ZnO target were investigated and compared by means of the Langmuir probe measurements in order to determine the mechanism of growth of porous Zn films during DC-mode Zn reactive sputtering. The power supplied to the magnetrons during the sputtering was kept at 125 W and the plasma was characterised as a function of oxygen content in the sputtering gas mixture, ranging from 0 to 60% for two gas pressures related to porous Zn film deposition, namely 3 mTorr and 5 mTorr. Based on the correlation of plasma properties measurements with scanning electron microscope imaging and X-ray diffraction of the films deposited under selected conditions it was found that the growth of porous, polycrystalline Zn films was governed by high electron density in the plasma combined with a high electron temperature and an increased energy of the ions impinging on the substrate.
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The aim of the present paper is to study the possibility of application of the X-ray quasi-forbidden reflection method to the composition determination of the sphalerite-type Cd_{1-x}M_{x}Te = Mg, Zn, Mn) single crystals. The method is based on the property of quasi-forbidden reflections that their integral intensity is very sensitive to composition and weakly sensitive to crystal lattice defects. An example of application for a Cd_{1-x}Mn_{x}Te single crystal is presented.
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Content available remote High-Pressure Diffraction Study of Ga_{1-x}Al_{x}As
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The Ga_{1-x}Al_{x}As sample of x=0.5 was prepared from a high quality single crystal grown by electroepitaxy on GaAs. The high-pressure diffraction experiments were performed using a diamond anvil cell and a germanium solid state detector. The zinc-blende phase is stable up to about 17.5 GPa on uploading. A high-pressure phase manifests itself at about 17 GPa, a complete phase change occurs at 18.7 GPa. On downloading, the zinc-blende phase reappears at about 10 GPa. The powder pattern of the high-pressure phase shows some similarities with the GaAs high pressure phases.
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The nanocrystalline state of the formally amorphous alloy Fe_{73.5}Cu_{1}Nb_{3}Si_{15.5}B_{7} is achieved by a heat treatment at temperatures between 500°C and 600°C. The XANES and EXAFS methods were applied for investigation of local structure and chemical bonding around Fe atoms in amorphous and nanocrystalline alloys. The Fe K absorption spectra were measured in the transmission mode at room temperature for Fe_{73.5}Cu_{1}Nb_{3}Si_{15.5}B_{7} amorphous and nanocrystalline alloys and compared with the spectra for Fe metallic foil and Fe_{3}Si polycrystalline samples.
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Content available remote Fabrication and Ferroelectric Properties of BiFeO₃/BaTiO₃ Heterostructures
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We report on preparation and electrical characterization of the epitaxial BaTiO₃ (BTO), BiFeO₃ (BFO) thin films and BFO/BTO bi- and multilayers, grown on (001) SrTiO₃ (STO) and (LaAlO₃)_{0.3}(Sr₂TaAlO₆)_{0.7} (LSAT) substrates. The ferroelectric properties were characterized using the electric force microscopy method to image and switch the electric domains. This fabrication process opens the routes towards wide study of magnetoelectric effect in complex oxide heterostructures.
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Content available Structural Properties of MnTe, ZnTe, and ZnMnTe
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Structural properties of ZnTe, MnTe, and Mn_{1-x}Zn_xTe alloy with zinc-blende, NiAs, and wurtzite phases were investigated by ab initio calculations. The calculated structural properties are in good agreement with the available experimental data. Theory predicts that the zinc-blende phase is more stable than wurtzite for all compositions. Mn_{1-x}Zn_xTe samples with 0.01 < x < 0.20 were grown by MBE. X-ray analysis of their crystalline structure revealed the presence of zinc-blende, wurtzite, and NiAs phases. The dominant phase changes from NiAs for the sample with x=0.01 to wurtzite for x=0.20. The observed stabilization of the wurtzite phase is possibly due to the hexagonal structure of the MnTe buffer.
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Content available remote Precipitates in Cd_{1-x}Ni_{x}Se Crystals Grown by the Bridgman Method
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Single crystals of Cd_{1-x}Ni_{x}Se alloys (x ranging from 0 to 0.075) were investigated using electron microprobe and X-ray diffraction. The analysis shows the presence of Ni-Se precipitates. The solubility limit of Ni is estimated to be 0.008.
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Content available remote Evolution of Pb_{1-x}Cd_{x}Te Solid Solution Structure at High Temperatures
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The recent successful growth of single, bulk Pb_{1-x}Cd_{x}Te crystals by self-selecting vapor transport method at the Institute of Physics of the Polish Academy of Sciences in Warsaw opened new opportunities to study the physical properties of this interesting material in detail. In this work we report the preliminary results of X-ray powder diffraction studies performed on a set of Pb_{1-x}Cd_{x}Te solid solutions (where x ≤ 0.056) at high temperatures (295 K ≤ T ≤ 1100 K) and analyzed with the Rietveld refinement. Our results demonstrate the necessity of some correction of the relevant phase diagram and of the solubility limit, known from the literature.
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Content available remote Anharmonic Optical Phonon Effects in ZnO Nanocrystals
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Zinc oxide (ZnO) is a very promising material for optoelectrical devices operating at the short-wavelength end of the visible spectral range and at the near UV. The Raman scattering studies of ZnO heterolayers formed by isothermal annealing show sharp phonon lines. In addition to the A_1(TO), E_1(TO), E_2^{H}, and E_1(LO) one-phonon lines, we observed two-phonon lines identified as: E_2^{H} - E_2^{L}, E_2^{H} + E_2^{L}, and 2LO at 332, 541, and 1160 cm^{-1}, respectively (at room temperature). The identification of the E_2^{H} - E_2^{L} peak was confirmed by its thermal dependence. Temperature dependent measurements in the range 6-300 K show that the phonon frequencies decrease with temperature. The E_2^{H} peak is at energy 54.44 meV (439.1 cm^{-1}), at 4 K and due to phonon-phonon anharmonic interaction, its energy decreases to 54.33 meV (438.2 cm^{-1}) at room temperature. The Grüneisen parameter found for this oscillation mode was γ_{E} 2H = 1.1 at about 300 K. The intensity of the E_2^{H} - E_2^{L} peak increases strongly with temperature and this dependence can be described by the Bose-Einstein statistics with activation energy of 13.8 meV (nearly equal to the energy of the E_2^{L} phonon).
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We analyse properties of thin SnTe layers and PbTe/SnTe heterostructures grown by MBE on BaF_{2}(111) substrates. Reflection high energy electron diffraction patterns registered during MBE growth of the samples as well as post-growth X-ray diffraction measurements evidence a high structural perfection of 0.6 μm thick SnTe layers and (50 Å PbTe)/(50 Å SnTe) superlattices. The full width at half maximum values of (222) X-ray rocking curves measured for these thin SnTe layers crystallized in the optimal MBE growth conditions are about 300 arcsec; the carrier concentrations can be tuned from 5×10^{19} cm^{-3} to 10^{2 1} cm^{-3} depending on the MBE process parameters.
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Content available remote Elastic Constants of β-HgS
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The elastic constants of single crystals of β-HgS highly doped with iron were directly determined at room temperature from the measurements of ultrasonic wave velocities by the pulse-echo technique. The values of c_{11}=6.750, c_{12}=5.186, and c_{44}=2.42 (given at 10^{10} N m^{-2} units) were obtained and compared with the experimental data taken for other mercury chalcogenides. The elastic characteristics of this group of materials is quite similar to those of Cd and Zn chalcogenides.
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Content available remote Ti-Al-N MAX Phase a Candidate for Ohmic Contacts to n-GaN
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Fabrication of a Ti₂AlN MAX phase for contact applications to GaN-based devices is reported. Sample characterisation was done by means of X-ray diffraction and secondary ion mass spectroscopy. Successful Ti₂AlN monocrystalline growth was observed on GaN and Al₂O₃ substrates by annealing sputter-deposited Ti, Al and TiN layers in Ar flow at 600°C. The phase was not seen to grow when the layers were deposited on Si (111) or when the first layer on the substrate was TiN. N-type GaN samples with Ti₂AlN layers showed ohmic behaviour with contact resistivities in the range 10¯⁴ Ωcm².
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Content available remote MBE Growth and Characterization of Cubic MnTe(111) on BaF_{2} Substrates
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We report on growth by molecular beam epitaxy of cubic MnTe(111) layers on BaF_{2} (111) substrates. Layers as thick as 0.2-1.0 μm were grown. Basic characterization by X-ray diffraction shows that the cubic crystal structure is deformed to orthorhombic symmetry.
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Content available remote Local Modes of Transition Metal Ions (Mn, Fe, Co) in Mercury Chalcogenides
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Optical phonons in mercury chalcogenides doped with selected transition metal ions are investigated by infrared reflectivity and Raman scattering measurements performed at helium temperatures. The results obtained for Hg_{1-x}Fe_{x}Se, Ηg_{1-x}Co_{x}Se, Ηg_{1-x}Fe_{x}S and Hg_{1-x}Co_{x}S mixed crystals demonstrate the significant influence of the 3d electron correlation effects and/or sp-d hybridization on the transition metal ion local mode frequency.
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