Copper solubility and distribution in doped GaSb single crystals

For the GaSb single crystals doped with copper (grown using the Czochralski method without encapsulant in flowing atmosphere of hydrogen) the distribution coefficient of copper in GaSb,k _eff=0.0021±0.0006 was found and the copper solubility in GaSb was discussed. The region of copper solubility in GaSb was analyzed on the thermodynamic basis using chemical phase diagram in the Sb?Ga?Cu system. Due to a rather low solubility of copper, its excessive amount in GaSb caused probably an increase of the dislocation density at the end of the GaSb single crystals.     

Hydrothermal crystal growth of the potassium niobate and potassium tantalate family of crystals

Single crystals of KNbO₃ (KN), KTaO₃ (KT), and KTa_1−xNb_xO₃ (x=0.44, KTN) have been prepared by hydrothermal synthesis in highly concentrated KOH mineralizer solutions. The traditional problems of inhomogeneity, non-stoichiometry, crystal striations and crystal cracking resulting from phase transitions associated with this family compounds are minimized by the hydrothermal crystal growth technique. Crystals of good optical quality with only minor amounts of metal ion reduction can be grown this way. Reactions were also designed to provide homogeneous distribution of tantalum and niobium metal centers throughout the KTN crystal lattice to maximize its electro-optic properties. Synthesis was performed at relatively low (500-660 °C) temperatures in comparison to the flux and Czochralski techniques. This work represents the largest crystals of this family of compounds grown by hydrothermal methods to date.     

Characterization of high-temperature superconductors by electron microprobe analysis

In order to optimize the physical properties of HTSC small single crystals grown from a melt for basic studies of their physical properties the influence of the environment on their impurity content was investigated by EPMA. This requires quantitative analysis of all elements being present in the crystals. The accuracy of results was affected by problems with the choice and quality of standards, by contamination but also by malfunction of microprobe electronics. The HTSC materials were found to react with mills, milling balls, crucibles and the atmosphere. These problems are being discussed and some reactions being studied for Y₁Ba₂Cu₃O_6+x (0 < x < 1) HTSC in A1₂O₃ and ZrO₂ crucibles. The crystals grown contain reproducible amounts of impurities depending on boundary conditions and exhibit a zone structure in composition particularly for Y and Ba within their range of homogeneity.     

Li doped and undoped ZnO nanocrystalline thin films: a comparative study of structural and optical properties

Thin films of ZnO were grown by the sol–gel method using spin-coating technique on (0001) sapphire substrates. The effect of doping after annealing on the structural and optical properties has been investigated by means of X-ray diffraction (XRD), cathodoluminescence (CL) spectrum, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The films that were dried at 623 K and then post annealed at 873 K showed (0002) as the predominant orientation. Two emission bands have been observed from CL spectrum. Lithium doped film shows shift in the near band edge UltraViolet emission peak and suppressed defect level emission peak in the visible range. SEM analysis of the films exhibits many spherical shaped nanoparticles. Roughness of the films determined using atomic force microscopy.      

Extraction - Spectrophotometric Determination of Phosphate Using N-Phenylbenzohydroxamic Acid

Abstract

A simple solvent extraction and spectrophotometric method for the determination of micro amount of phosphate (PO₄) is described. Phosphate is selectively separated from associated elements by reacting it with calcium and extracting excess calcium with N-phenylbenzohydroxamic acid (PBHA) at pH 11.3. The excess calcium was determined in ultra-violet and visible region and hence the phosphate content was calculated. The Beer's law is obeyed in the range 0.5 ? 10.0 ppm at 340 nm and 0.25 - 8.0 ppm at 560 nm of phosphate for a fixed amount of calcium (20.0 ppm). These results are also compared with those obtained by atomic absorption spectrophotometry. The method has been applied for the determination of phosphate in pharmaceutical and other samples.     

Colors of mixed-substituted double molybdate single crystals having scheelite structure

X-ray diffraction, neutron diffraction, optical and absorption spectroscopy, electron probe microanalysis, and temperature-dependent electrical conductivity measurements were used to study structural features and defect generation to be responsible for coloring of single crystals of nominal compositions (Na_0.5La _x Gd_{0.5 ? x} )MoO₄:Tm having scheelite structure which were Czochralski grown under a weakly oxidizing atmosphere followed by air annealing. In nonannealed crystals, the color was found to be due to oxygen vacancies and their compensator electrons (black color) and, most likely, electrons located on Mo6+ ions (lilac color); the concentration of these defects decreased upon air annealing, thereby discoloring the samples. The yellow color of crystals was interpreted as arising from possible formation of a color center (an association of a molybdenum vacancy and a hole).     

Formation and tribological properties of composite Langmuir–Blodgett films of stearic acid with molybdenum disulfide and amorphous carbon

The morphology and tribological properties of Langmuir–Blodgett mono- and bilayers of stearic acid with particles of molybdenum disulfide (MoS₂) and amorphous carbon (С), prepared on silicon and steel substrates by horizontal deposition (stearic acid–MoS₂ and stearic acid–С monolayers) and by the “roll” technique (stearic acid–MoS₂/stearic acid–С bilayers), were studied. Incorporation of C and MoS₂ particles into the structure of a stearic acid film enhances its wear resistance by a factor of 2.8 and 5.5, respectively. The presence of MoS₂ and С particles and of their aggregates of size from ~220 nm to 16.3 μm in stearic acid layers was confirmed by atomic force microscopy.     

On the clathrate form of elemental silicon,Si136: preparation and characterisation of NaxSi136 (x→0)

The clathrate form of silicon, Si₁₃₆ (otherwise known as Si₃₄), having a residual sodium content as low as 35 ppm (i.e., x∼0.0058 in Na_xSi₁₃₆), has been prepared by thermal decomposition of NaSi under high vacuum, followed by several other treatments under vacuum, and completed by repeated reactions with iodine. The residual amount of sodium has been determined by a combination of analytic and spectroscopic methods involving XRD, electron probe microanalysis, atomic absorption, NMR and EPR. This latter technique proved to be very appropriate to the characterisation of very diluted sodium atoms in such clathrate structure and to the quantitative determination of its residual concentration.     

Application of bromine trifluoride for pre-concentration and determination of rare-earth elements in fuel uranium dioxide

Radioactive indicator's (¹⁵²Eu) method was used to study the behavior of rare-earth element (REE) micro-impurities at fluorination of fuel UO₂ with bromine trifluoride. The proposed process is very simple and carried out under a blanket layer of Freon-113 in the glassy carbon (vitreous) crucibles.It was shown that uranium matrix completely removes from reaction sphere in the form of UF₆ and REE contaminations quantitatively remain in crucible owing to practical non-volatility of their fluorides. High purity of fuel UO₂ causes small amount of the non-volatile rest (0.3-2 wt.% from initial weight) that considerably facilitates a problem of confident diagnostics of the strictly limited REE content in this material. Removal of uranium and concentration of REE from analyzed test samples via fluorination is several hundred times more rapid scheme of pre-sampling to atomic emission spectral determination of REE micro-quantities in UO₂ than traditionally used extraction and ion-exchange ways of the preliminary concentration of contaminations and removal of uranium.     

MoO3, WO3 Single and Binary Oxide Prepared by Sol-Gel Method for Gas Sensing Applications

MoO₃, WO₃ single and Mo/W binary compounds at different Mo/W atomic percentages were deposited by sol-gel spin coating technique on Si/Si₃N₄ substrates provided with Pt interdigital electrodes and annealed at 450°C for 1 h. Films were characterized by SEM, grazing incidence XRD and XPS techniques. Electrical responses to different gases were obtained by exposing the films to 30 ppm CO and 1 ppm NO₂. Increasing the Mo/W content the selectivity to NO₂ is enhanced. Gas responses resulted to be influenced by the Mo/W weight ratio, films morphology and amount of crystalline phases.     

Time-of-flight mass spectroscopy of femtosecond and nanosecond laser ablated TeO2 crystals

Single-pulse femtosecond (fs) (pulse duration ～200 fs, wavelength 398 nm) and nanosecond (ns) (pulse duration 4 ns, wavelength 355 nm) laser ablation have been applied in combination with time-of-flight mass spectrometer (TOFMS) to analyze the elemental composition of the plasma plume of single-crystalline telluria (c-TeO₂, grown by the balance controlled Czochralski growth method). Due to the three-order difference of the peak intensities of the ns and fs-laser pulses, significant differences were observed regarding the laser-induced species in the plasma plume. Positive singly, doubly and triply charged Te ions (Te⁺, Te₂⁺, Te₃⁺) in the form of their isotopes were observed in case of both irradiations. In case of the ns-laser ablation the TeO⁺ formation was negligible compared to the fs case and there was no Te trimer (Te₃⁺) formation observed. It was found that the amplitude of Te ion signals strongly depended on the applied laser pulse energy. Singly charged oxygen ions (O⁺) are always present as a byproduct in both kinds of laser ablation.     

Experimental and theoretical determination of the saturation vapor pressure of silicon in a wide range of temperatures

Reference books and original studies devoted to the determination of the saturation vapor pressure of silicon in a wide range of temperatures have been analyzed. It has been established that no reliable experimental data in the range of high temperatures (above 2000 K) are available in the literature. It has been demonstrated that there is a need to perform additional theoretical and experimental investigations with the use of different methods. The total pressure and partial pressures of Si _n (n = 1−6) molecules over liquid silicon are calculated in the temperature range 1700–3400 K. The calculation of the composition of the gas phase over the “Si(l)-container” systems is performed. Materials of the crucibles intended for the use in experimental investigations of the temperature dependence of the saturation vapor pressure of silicon over the liquid phase are recommended.     

Crystal growth and thermodynamic properties of lithium tungstate doped by 4% molybdenum

For the first time, single crystal of Li₂W_0.96Mo_0.04O₄ has been grown by low-temperature-gradient Czochralski technique. The thermodynamic characteristics (standard formation enthalpy and lattice enthalpy) that are necessary to improve the growth technology have been studied by solution calorimetry. For Li₂W_1–xMo_xO₄ single crystals, correlations of lattice enthalpies and standard formation enthalpies with tolerance factor were found.     

Growth and characterization of 2-amino-4-picolinium 4-aminobenzoate single crystals

The organic material of 2-amino-4-picolinium 4-aminobenzoate (C₆H₉N₂⁺·C₇H₆NO₂^?) was synthesized and grown as single crystals at room temperature by slow evaporation solution growth technique in the constant temperature bath (±0.01 °C) using ethanol as solvent. The grown crystals were characterized by XRD and FT-IR spectral analyses. The melting point, density, UV–visible spectral studies were carried out for the grown crystals. The theoretical factor group analysis predicts 372 internal modes of vibration and optical modes in the grown title compound. The second harmonic generation (SHG) output of 2-amino-4-picolinium 4-aminobenzoate was recorded by Kurtz–Perry powder technique and it is found to be 355 mV at a given pulse energy of 1.45 mJ/s and for urea the SHG output was 525 mV. The dielectric behaviour of 2-amino-4-picolinium 4-aminobenzoate was investigated with different frequencies and temperatures.     

Determination of antimony dopant and some ultra-trace elements in semiconductor silicon by atomic absorption spectrometry with introduction of solid samples into the furnace

Antimony as a dopant at a level of ca. 35 atom/10⁶ atoms (ppm, atomic) and ultra-trace concentrations of lead and manganese (<0.02 ppm, atomic) are determined in semiconductor silicon by atomic absorption spectrometry after introduction of milligram samples of silicon to a pyrolytically-coated graphite furnace. Calibration was done with standard aqueous solutions. Iron, silver, zinc and cadmium were sought but were at concentrations below the limits of detection. The graphite microboats used for sample introduction were useful for only 3–10 samples because of silicon carbide formation.     

Linear and third order nonlinear optical properties of LiRbB4O7 single crystal

Lithium rubidium borate (LiRbB₄O₇) single crystal has been grown by the Czochralski method. Crystalline perfection and optical homogeneity of the grown LiRbB₄O₇ crystal are analyzed by high resolution X-ray diffraction and birefringence interferometric technique, respectively. Third order nonlinear optical parameters of LiRbB₄O₇ crystal are determined by Z-scan experimental technique. The nonlinear refractive index (n₂) and third-order nonlinear optical susceptibility (χ³) are estimated to be −4.935 × 10⁻¹¹ cm²/W and 2.719 × 10⁻⁷ esu, respectively. The measured (n₂) value reveals the self-focusing nature of LiRbB₄O₇ crystal.     

Single-walled carbon nanotubes as stationary phase in gas chromatographic separation and determination of argon, carbon dioxide and hydrogen

A chromatographic technique is introduced based on single-walled carbon nanotubes (SWCNTs) as stationary phase for separation of Ar, CO₂ and H₂ at parts per million (ppm) levels. The efficiency of SWCNTs was compared with solid materials such as molecular sieve, charcoal, multi-walled carbon nanotubes and carbon nanofibers. The morphology of SWCNTs was optimized for maximum adsorption of H₂, CO₂ and Ar and minimum adsorption of gases such as N₂, O₂, CO and H₂O vapour. To control temperature of the gas chromatography column, peltier cooler was used. Mixtures of Ar, CO₂ and H₂ were separated according to column temperature program. Relative standard deviation for nine replicate analyses of 0.2 mL H₂ containing 10 μL of each Ar or CO₂ was 2.5% for Ar, 2.8% for CO₂ and 3.6% for H₂. The interfering effects of CO, and O₂ were investigated. Working ranges were evaluated as 40-600 ppm for Ar, 30-850 ppm for CO₂ and 10-1200 ppm for H₂. Significant sensitivity, small relative standard deviation (RSD) and acceptable limit of detection (LOD) were obtained for each analyte, showing capability of SWCNTs for gas separation and determination processes. Finally, the method was used to evaluate the contents of CO₂ in air sample.     

Thermodynamic characteristics of sodium ditungstate single crystal

The single crystal of Na₂W₂O₇ has been grown by the low-temperature-gradient Czochralski technique. The thermo- dynamic properties (standard enthalpy of formation, lattice enthalpy and stabilization energy), the knowledge of which is necessary to improve the growth technology, have been measured using reaction calorimetry. It has been shown that in the Na₂W₂O₇– Na₂Mo₂O₇ series, the luminescence wavelength increases from 540 to 650 nm, respectively, along with a change in the lattice enthalpy from −49030 to −54730 kJ mol⁻¹.     

Microanalytical characterization of inclusions in Cr-doped LEC GaAs

Inclusions of different morphologies were observed by Infrared (IR) microscopy and Scanning Electron Microscopy (SEM) in the last-to-freeze region of a Cr-doped GaAs single crystal grown by the Liquid Encapsulated Czochralski (LEC) technique.Energy dispersive X-ray analysis (EDX) revealed that these inclusions consist of different chromium compounds. Compositions correspond to the following binary phases and compounds: CrGa₄, Cr₃As₂, Cr₂As₃. Additionally, the quasi-ternary system of Cr₃Ga₄ + CrAs has been found. Sometimes, additional carbon particles have been detected within the heterogeneous inclusions. The possible generation mechanism of inclusions under supercritical growth conditions is discussed.Dedicated to Professor Dr. rer. nat. Dr. h. c. Hubertus Nickel on the occasion of his 65th birthday     

High-temperature conductivity relaxation in undoped CdS and CdSe single crystals

The high-temperature conductivity (HTC) relaxation in CdS and CdSe single crystals, caused by a steep change of cadmium vapor pressure P_Cd, was measured. For obtaining a steep change of P_Cd improved van Doorn equipment was used. Conductivity measurements were carried out using the Van der Pauw method. It was shown that the Cd diffusion from gaseous phase into CdS and CdSe platelets leads to a conductivity time-dependence function σ(t) in the form of a sum of decreasing exponents, indicating that the rate of HTC relaxation is limited by the chemical diffusion of cadmium. A correlation between chemical and tracer-diffusion coefficients was found. Values of activation energies and preexponential factors for both types of diffusion were determined. The results are discussed using a model for transformation of Cd^··_i into V^··_S,Se previously proposed by Chern and Kröger for chemical self-diffusion in CdTe.