Synthesis,characterization and optical properties of ZnO nanoparticles with controlled size and morphology

Zinc oxide monodispersed nanoparticles were synthesized using a modified polyol process without any requirement to use a catalyst or calcination step at high temperature. The morphology and the size of the resulting oxide particles were adjusted by using several synthesis parameters (temperature, alkaline ratio, hydrolysis ratio, etc.). The increasing of the alkaline ratio results in a great change of the elaborated particles morphology that evolved from irregular and anisotropic forms (conical, nanorod-like and elliptical) to spherical one. A growth mechanism of these particles was proposed on the basis of zincite crystal structure and the morphology evolution as a function of the synthesis parameters. The photoluminescence spectra show UV-excitonic and visible emission bands. The strongest intensity of the visible emission was observed in nanorod-like particles, which implies an increased fraction of oxygen vacancies in this sample. The rod-like particles with 1 μm length show the dominant UV-emission, which evidences their improved stoichiometry.     

Preparation of single-crystalline ZnO films on ZnO-buffered a-plane sapphire by chemical bath deposition

High-quality zinc oxide (ZnO) films were successfully grown on ZnO-buffered a-plane sapphire (Al₂O₃ (1 1 2¯ 0)) substrates by controlling temperature for lateral growth using chemical bath deposition (CBD) at a low temperature of 60 °C. X-ray diffraction analysis and transmission electron microscopy micrographs showed that the ZnO films had a single-crystalline wurtzite structure with c-axis orientation. Rocking curves (ω-scans) of the (0 0 0 2) reflections showed a narrow peak with full width at half maximum value of 0.50° for the ZnO film. A reciprocal space map indicated that the lattice parameters of the ZnO film (a=0.3250 nm and c=0.5207 nm) were very close to those of the wurtzite-type ZnO. The ZnO film on the ZnO-buffered Al₂O₃ (1 1 2¯ 0) substrate exhibited n-type conduction, with a carrier concentration of 1.9×10¹⁹ cm⁻³ and high carrier mobility of 22.6 cm² V⁻¹ s⁻¹.     

Synthesis and ammonia sensing property of Ag3CuS2 nanocages obtained from Cu7S4 18-facet hollow nanopolyhedra

Ag₃CuS₂ nanocages were successfully fabricated for the first time via a convenient ion-exchange route by Ag⁺ reacting with Cu₇S₄ 18-facet hollow nanopolyhedra. The average size and shell thickness of Ag₃CuS₂ nanocages were around 400 and 30 nm, respectively. Room-temperature response of Ag₃CuS₂ nanocages to ammonia was investigated by photoluminescence-type sensor. Sensing results suggested that these hollow-structured Ag₃CuS₂ exhibited better performances including higher sensitivity, shorter response and recovery time than their rod-shape counterparts. A possible hole trapping mechanism was proposed.     

Synthesis and characterization of single-crystalline PrCO3OH dodecahedral microrods and its thermal conversion to Pr6O11

Single-crystalline PrCO₃OH dodecahedral microrods with an orthorhombic structure have been successfully synthesized by the hydrothermal method used urea as the precipitator. Pr₆O₁₁ dodecahedral microrods have been obtained by thermal conversion of PrCO₃OH dodecahedral microrods at 600 °C in air for 6 h. The as-synthesized products were characterized by X-ray powder diffraction, field-emission scanning electron microscope, transmission electron microscopy, high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray photoelectron spectra, fourier transform infrared spectroscopy and thermogravimetry–differential thermal analysis. The effect of the reaction parameters on the morphology of the product has been investigated. The dodecahedral microrods with larger size and better crystallinity can be obtained under the higher reaction temperature. The possible formation mechanism of PrCO₃OH microrods was discussed.     

Bulk single-crystal growth of ternary AlxGa1−xN from solution in gallium under high pressure

We have successfully grown bulk, single crystals of Al_xGa_1−xN with the Al content x ranging from 0.5 to 0.9. Samples were grown from Ga melt under high nitrogen pressure (up to 10 kbar) and at high temperature (up to 1800 °C) using a gas pressure system. The homogeneity and Al content of the crystals were investigated by X-ray diffraction and laser ablation mass spectrometry. On the basis of the high-pressure experiments, the corresponding pressure–temperature (p–T) phase diagram of Al–Ga–N was derived. The bandgap of the material was determined by the femtosecond two-photon absorption autocorrelation method and is equal to 5.81±0.01 eV for the Al_0.86Ga_0.14N crystals.     

Synthesis and growth mechanism of rough PbTe polycrystalline thermoelectric nanorods

Rough PbTe polycrystalline one-dimensional nanostructure is expected to exhibit improved thermoelectric properties, compared to single-crystal one. In this article, polycrystalline PbTe thermoelectric nanorods with rough surfaces are successfully synthesized with or without surfactants by a simple alkaline reducing chemical route. Microstructural analyses show that these nanorods range from 50 to 200 nm in diameter with lengths up to 1 μm, and are composed of PbTe nanoparticles of about 30–50 nm. The formation mechanism of PbTe nanorods can be reasonably explained by tellurium template-based process from the time-dependent experiments.     

Single crystals growth and absorption spectra of Cr-doped Al2−xInx(WO4)3 solid solutions

The growth conditions of pure and Cr³⁺-doped Al_2−xIn_x(WO₄)₃ single crystals, using top-seeded solution growth (TSSG) technique, have been studied. A series of experiments have been performed at different In concentrations, x=0.0, 0.3, 0.6 and 1.0, as well as at different concentrations of Cr³⁺ (0.0, 0.1, 0.2, 0.5 and 1.0) in at% with respect to the initial total concentration of Al and In in the starting solutions. The basic parameters of the crystal growth are varied over a wide range: seed orientation, speed of rotation, axial and radial temperature differences in the solution and the solution cooling rate. The investigated relations between the basic defects in the crystals and these parameters result in determination of the optimal conditions for growth of defect-free crystals. Distribution coefficients of Al, In and Cr have been determined, so the growth of crystals with given compositions is possible. Values of Dq/B (crystal field strength) for the various crystal compositions are calculated from the optical absorption spectra. The calculated values show that the discussed solid solutions have weak crystal field and are suitable for media with broadband emission spectra.     

Properties of gallium- and aluminum-doped bulk ZnO obtained from single-crystals grown by liquid phase epitaxy

Bulk properties of gallium (Ga)- and aluminum (Al)-doped zinc oxide (ZnO) were studied using bulky single-crystalline thick films grown by liquid phase epitaxy (LPE). The highest possible dopant concentration was 1×10¹⁹ cm^–3 for LPE growth at around 800 °C. The electron concentration was nearly same to the Ga and Al concentrations. The donor binding energy decreased to nearly zero with an increase in dopant concentration, and electron mobility of the sample with relatively high dopant concentration (1×10¹⁹ cm^–3) was more than 60 cm² V^–1 s^–1 at room temperature. The LPE technique is a potential solution for the production of ZnO for optical applications because the well-defined excitonic luminescence could be seen from the LPE-grown-doped single-crystals.     

Physical properties of ZnSe films prepared by two-source evaporation and a study of post doping effect

Two-source thermal evaporation method was utilized to prepare hard ZnSe thin films, the films were then immersed in silver nitrate solution for different time periods. The optical properties of the films were measured from the transmittance spectra. X-ray pattern of the films were also included. Final compositions of the resulting films were measured by EMPA method and comparisons between compositions by EMPA vs. optical absorbance were also reported. The dc electrical conductivity increased and a small shift in the optical band gap was also observed.     

Synthesis,characterization and growing mechanism of monodisperse Fe3O4 microspheres

Monodisperse Fe₃O₄ microspheres assembled by a number of nanosize tetrahedron subunits have been selectively synthesized through the hydrothermal process. The synthesized Fe₃O₄ microspheres have good dispersibility. The subunits made up of microspheres were uniform in size and like-tetrahedron in shape. The average diameter of each Fe₃O₄ microsphere is about 50–55 μm. The length of each edge of tetrahedron is about 100 nm. A series of experiments had been carried out to investigate the effect of reductant, precipitator and reaction time on the formation of Fe₃O₄ microsphere and tetrahedron subunits. The results show that ascorbic acid as reductant and urea as precipitator supplied a relatively steady environment during the synthesis process and led to the formations of Fe₃O₄ tetrahedron subunit and monodisperse Fe₃O₄ microspheres. As the reaction time increased from 3 to 24 h, the Fe₃O₄ microspheres tended towards dispersion and becoming large in size from 10–20 to 50–55 μm, and the subunits formed Fe₃O₄ microspheres that varied from spheroid to tetrahedron and from a small nanoparticle (20–30 nm) to a large one (90–110 nm). A reasonable explanation for the formations of the Fe₃O₄ microsphere and the tetrahedron subunit was proposed through Ostwald ripening and the attachment growth mechanism, respectively.     

Floating-zone growth of large high-quality CoAl2O4 single crystals

We report the first successful floating-zone growth of high-quality CoAl₂O₄ single crystals with volume up to 1 cm³ free from inclusions and sub-grains. The neutron rocking curves of the CoAl₂O₄ crystal have the width of about 0.30 degree proving the excellent quality of the grown samples. X-ray synchrotron experiments show that crystals have spinel structure with the lattice constant a₀=8.09853(1) Å. Magnetization measurements give the effective magnetic moment μ_eff=4.63 μ_B per Co⁺² ion in a good agreement with previous measurements on ceramic samples.     

Growth and characterization of Ytterbium doped KGd(WO4)2 single crystal

Single crystals of Ytterbium doped KGd(WO₄)₂ were grown by Top Seeded Solution Growth technique using K₂WO₄ as flux system. The growth parameters were optimised to get optically transparent crystals. Variation in the lattice parameters were observed in comparison to the pure KGd(WO₄)₂ crystals. The absorption spectra recorded for the Yb:KGW confirms the material suitability for diode pumped solid state lasers. The vibrational studies carried out using spontaneous Raman spectra indicate the strong anionic vibration of the material. PL spectra show the lasing channel of the laser active ions present. Stimulated Raman scattering analysis confirms the material as an efficient Raman laser material. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study on the growth and interfacial strain of CoFe2O4/BaTiO3 bilayer films

CoFe₂O₄/BaTiO₃ bilayer films were epitaxially deposited on SrTiO₃ substrates by laser molecular beam epitaxy (LMBE). The growth process of the bilayer films was in-situ monitored by reflection high-energy electron diffraction (RHEED). Sixty nanometer thick-BTO layer was firstly fabricated in a layer-by-layer growth mode with an atomic smooth surface. CFO films with a varying thickness ranging from 5 to 60 nm were subsequently deposited on BTO-coated STO substrates. The different growth behaviors of CFO films were observed due to the lattice mismatch strain. Between two short stages of the growth mode transforming, a long duration with Stransky and Krastonov growth mode was maintained. Strainfully relaxed CFO film in the island growth mode was finally formed. High-resolution X-ray diffraction (HRXRD) was used to further analyze the strain effect. It was found that the tensile stress imposed on BTO by CFO was strengthened with increasing the thickness of CFO films, which could lessen the distortion of BTO by counteracting the compressive stress caused by STO substrates. The strengthened tensile stress weakened the ferroelectric property of BTO films by reducing structural tetragonality, which was demonstrated by polarization-electric (P-E) measurement.     

Phase and morphology controllable synthesis of Sb2O3 microcrystals

A simple and facile solution route has been developed for phase and morphology controllable synthesis of antimony trioxide (Sb₂O₃) microcrystals. Orthorhombic phase and cubic phase Sb₂O₃ microcrystals have been selectively synthesized in high yield. The products were characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The as-obtained microcrystals exhibited a variety of morphologies and structures, such as microspindles, nanoplates, and octahedra. Several experimental parameters have been investigated to gain morphology control of Sb₂O₃ microcrystals. Based on the time-dependent experimental results, an aggregation, and recrystallization mechanism was proposed to describe the formation process of these novel microstructures.     

Effects of Li replacement on the nucleation, crystallization and microstructure of Li2O-Al2O3-SiO2 glass

The Li replacement including the Li₂O replaced by other oxides and the expensive Li₂CO₃ replaced by low-cost spodumene mineral was studied to lower the product cost of (Li₂O-Al₂O₃-SiO₂, LAS) glass ceramic, and the effects of Li replacement on the nucleation, crystallization and microstructure of LAS glass were investigated by the differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that Li₂O replacement increases the crystallization activation energy, lowers the crystal growth, and increases the nucleation and crystallization temperature by restraining the formation of crystalline phases. The Li₂CO₃ replacement decreases the crystallization activation energy, promotes the crystal growth, without affecting the nucleation, and lowers the crystallization temperature by adding some beneficial compositions with mixed alkali effect.     

Crystal growth and characterization of K2B4O11H8

Single crystals of K₂B₄O₁₁H₈, a non-centrosymmetric borate material, have been prepared by slow evaporation of water solution at room temperature. The crystals were colorless and transparent with smooth faces. The single-crystal X-ray diffraction analysis showed that K₂B₄O₁₁H₈ crystallized in the orthorhombic space group P2₁2₁2₁ with a=6.8556(6) Å, b=11.7787(12) Å, c=12.8949(14) Å, Z=4, R₁=0.0188, and wR₂=0.0464. The powder X-ray diffractometry (PXRD), infrared spectrum, transmittance spectrum, TG–DTA curves and second harmonic generation properties of title compound have been determined.     

Raman and ATR FTIR spectroscopy in reactive crystallization: Simultaneous monitoring of solute concentration and polymorphic state of the crystals

Batch-reactive crystallization of the two polymorphs of l-glutamic acid was studied using in-line Raman and ATR FTIR spectroscopy. It was observed that the barrier to the nucleation of the stable β-form was higher, and thus the occurrence of β-form nucleation requires a higher supersaturation level. The local supersaturation level inside the reactive crystallizer is significantly affected by the feeding manner of the reactant. When the reactant was fed to a poorly mixed zone, such as the surface of the liquid, a high local supersaturation level was generated near the feeding point. This high local supersaturation level drastically increased with the increase in the concentrations of the reactants. As a consequence, the fraction of the β-form increased with the increase in reactants concentrations. On the other hand, feeding the reactant to a well-mixed zone near the impeller can avoid the occurrence of high local supersaturation, and therefore the dependence of the polymorphic composition of the final product on the concentration of the reactants can be reduced. The information obtained from the spectroscopy leads to improved understanding of the precipitation process and offers great potential for process optimization and control of crystalline quality.     

Self-sacrificed template method for the synthesis of ZnO-tubular nanostructures:reaction kinetics and pathways

Using Zn nanowires as a self-sacrificed template, hierarchical tubes constructed by zinc oxide (ZnO) nanoflakes and ZnO nanotubes have been successfully fabricated by two different thermal-oxidation modes. The products were characterized by the X-ray powder diffraction, transmission electron microscopy and field-emission scanning electron microscopy. The experimental results show that the formation processes of ZnO nanostructures are sensitive to the growth temperature, which is lower or higher the melting point of Zn (419 °C). ZnO nanoflake tubes and ZnO nanotubes can be controlled through the variation of the heat-treatment process of Zn nanowires and their growth pathway can be described by two types of growth mechanism, in terms of Kirkendall effect and the sublimation of the Zn cores, respectively. Our method provides an easy and convenient way to prepare metal oxides tubular nanostructures with different morphologies through self-sacrificed template method via adjusting the heat-treatment process.     

Glasses and glass-ceramics in the oxyfluoride ternary system Pb(PO3)2-WO3-PbF2

Glasses were prepared by the melt-quenching method in the ternary system Pb(PO₃)₂-WO₃-PbF₂ and doped with Er³⁺ in order to prepare luminescent transparent glass-ceramics. This work focused on thermal and structural characterization of tungsten lead-phosphate glasses and crystallization study for preparing transparent glass-ceramics. Thermal properties such as thermal stability and crystallization behavior upon heating were investigated by DSC in function of PbF₂ content. For low PbF₂ concentrations, only one crystallization peak due to Pb₃(PO₄)₂ is observed whereas samples containing more than 15% of PbF₂ present another exothermic event at lower temperatures related with precipitation of PbF₂, Pb₂P₂O₇ and Pb₂OF₂. Structural investigations by Raman spectroscopy suggest that PbF₂ modifies the tungsten-phosphate network through the formation of P―F and P―O―Pb bonds but the average network connectivity remains almost constant. A crystallization study has been performed by DSC to investigate the dominant crystallization mechanisms in these glasses and it has been established that Pb₃(PO₄)₂ is nucleated on the surface whereas PbF₂, Pb₂P₂O₇ and Pb₂OF₂ crystallize dominantly from the glassy bulk. Transparent glass-ceramics containing nanosized PbF₂ crystallites were also prepared by suitable heat-treatment on the glass sample containing 20% of PbF₂ and Raman microscopy of these glass-ceramics supports the crystallization mechanisms determined by DSC.     

Growth,thermal and optical properties of a new nonlinear optical crystal: ZnBi2B2O7

Single crystals of ZnBi₂B₂O₇ (ZBBO) have been successfully grown by the top-seeded growth method from a high-temperature melt. The crystal was colorless and transparent with size of 15×10×5 mm³. The orientation of ZBBO crystal has been discussed. The melting point, molar enthalpy of fusion, and molar entropy of fusion of the crystal were determined to be 964.02 K, 110680.36 J mol⁻¹, and 113.92 J K⁻¹ mol⁻¹, respectively. The transparency range of the crystal extends from 370 to 2100 nm.