Growth characteristics of ultra long double-ended acicular ZnO synthesized by a hydrothermal process

Double-ended acicular ZnO structure can be synthesized via a hydrothermal process with tetramethylammonium hydroxide and zinc acetate as precursors and polyvinyl alcohol (PVA) as a structure-directing agent. The as-prepared ZnO products show the well crystalline wurtzite structure with growth direction along [0 0 0 1]. For the first time, PVA is found to be employed as a reservoir of Zn²⁺ ions in the present study, and can control the concentration of Zn²⁺ in reaction solution, and the acicular morphology can be formed at the two ends of the 1-D ZnO structure, due to the effect of secondary growth that occurs as the sufficient concentration of Zn²⁺ ions chelated by PVA releasing to the reaction solution. Furthermore, the size of the 1-D ZnO structure can be tuned by different amounts of PVA addition.     

Synthesis,growth mechanism and optical characterization of zinc nitride hollow structures

In this report, we describe the noncatalytic and template-free synthesis of zinc nitride (Zn₃N₂) novel microstructures with hollow interiors via simple nitridation reaction of zinc powder at optimum temperature of 600° C for 120 min in ammonia gas environment under atmospheric pressure. Hollow microstructures obtained were mostly of spherical shape with diameters in the range 8–35 μm and with open mouth on the surface. The growth mechanism has been proposed for the elucidation of hollow structures formation. Crystal structure and phase purity of the product were investigated by X-ray diffraction (XRD) characterization and energy dispersive X-ray spectroscopy (EDS) analysis confirmed the chemical composition of the product. Morphology of the as-prepared product was investigated using scanning electron microscopy (SEM). Ultraviolet–visible–near infrared (UV–vis–NIR) spectrophotometry was used to study the transmittance behaviour of zinc nitride microstructures and thereby an indirect optical band gap of 2.81 eV was calculated using Davis–Mott model. Room temperature photoluminescence (PL) studies exhibited two prominent peaks of the product; one very strong peak near band edge UV emission (395 nm) and other comparatively suppressed and broad peak at orange luminescence emission (670 nm).     

Scale-up synthesis of zinc borate from the reaction of zinc oxide and boric acid in aqueous medium

Synthesis of zinc borate was conducted in a laboratory and a pilot scale batch reactor to see the influence of process variables on the reaction parameters and the final product, 2ZnO·3B₂O₃·3.5H₂O. Effects of stirring speed, presence of baffles, amount of seed, particle size and purity of zinc oxide, and mole ratio of H₃BO₃:ZnO on the zinc borate formation reaction were examined at a constant temperature of 85 °C in a laboratory (4 L) and a pilot scale (85 L) reactor. Products obtained from the reaction in both reactors were characterized by chemical analysis, X-ray diffraction, particle size distribution analysis, thermal gravimetric analysis and scanning electron microscopy. The kinetic data for the zinc borate production reaction was fit by using the logistic model. The results revealed that the specific reaction rate, a model parameter, decreases with increase in particle size of zinc oxide and the presence of baffles, but increases with increase in stirring speed and purity of zinc oxide; however, it is unaffected with the changes in the amount of seed and reactants ratio. The reaction completion time is unaffected by scaling-up.     

Synthesis, growth of organic nonlinear optical crystal: Semicarbazone of 2-amino-5-chloro-benzophenone (S2A5CB) and its characterisation

A new organic crystal of semicarbazone of 2–amino–5–chloro–benzophenone has been grown as a single crystal by slow evaporation solution growth technique for the first time in the literature. The grown crystal has been characterised by proton nuclear magnetic resonance spectral analysis and single crystal and powder X-ray diffraction studies. Functional groups of the crystallised molecules were confirmed by FT-IR and FT-Raman analyses. Mechanical strength of the crystals was studied by microhardness test. Optical transparency of the grown crystals has been studied by UV-Visible spectra. The second harmonic generation property of the compound was analysed.     

Large-scale synthesis of ZnSe nanoribbons on zinc substrate

ZnSe nanoribbons have been successfully synthesized on a large scale by solvothermal treatment of Zn and Se powder in the mixture of hydrazine hydrate and diethanolamine at 140 °C for 24 h and subsequent annealing in Ar. The morphology of the final products strongly depended on the volume ratio of hydrazine hydrate and diethanolamine. Scanning electron microscopy (SEM) explorations indicated that the as-prepared ZnSe nanoribbons were mostly about 40 nm in thickness, 100 nm in width, and 50 μm in length. X-ray diffraction pattern (XRD) and transmission electron microscopy (TEM) investigations confirmed that resulting ZnSe nanoribbons are wurtzite structures and have a [0 0 1] growth direction. PL (photoluminescence) spectrum of the products exhibited a visible light emission. Based on these investigations, the products were expected to find wide applications in optoelectronic, field emission and catalytic fields.     

Synthesis, growth and characterization of Bis S-benzylisothiouronium tetrachlorido zincate (II) a semiorganic nonlinear optical crystal

A new semiorganic nonlinear optical (NLO) crystal, Bis S-benzylisothiouronium tetrachloridozincate (II) (SBTTZ), has been synthesized and good optical quality needle shaped single crystals of the title material were grown by solvent evaporation solution growth method at room temperature. Powder X-ray diffraction pattern confirms the crystallinity of the material. Single X-ray diffraction study was carried out to establish the existence of intermolecular hydrogen bonding in the crystal. The UV–Vis–NIR spectrum indicates that the crystal has very good transmittance in the entire visible and near IR regions of the spectrum suggesting the suitability of the material for NLO applications. The presence of various functional groups was confirmed by FT IR spectroscopic technique. The ¹H NMR spectrum confirms the molecular structure. The thermal and mechanical stabilities have been confirmed by TG/DTA analyses and Vickers microhardness study respectively. The SHG in the grown crystal was identified by modified Kurtz–Perry method using Nd:YAG laser as the source.     

Eutectic structures in the Ni–Co–Cr–Al system obtained by plasma spraying and by Bridgman growth

Formation of a regular fibrous two-phase microstructure was found in low-pressure plasma spray (LPPS) deposited Ni–Co–Cr–Al–Y coatings by transmission electron microscopy and analyzed by energy dispersive spectroscopy. The structure is compared to aligned lamellar three-phase structures of an Ni–Co–Cr–Al alloy obtained on Bridgman growth under slow unidirectional solidification (UDS) conditions. The composition of the Ni–Co–Cr–Al alloy for UDS experiments has been identified by DTA. The conditions for the formation of both the LPPS and the UDS structures are discussed.     

Crystallization behavior and hydrophilic performances of V2O5–TiO2 films prepared by sol–gel dip-coating

Homogeneous and transparent V₂O₅–TiO₂ composite nanometer thin films were prepared on glass substrates by sol–gel processing and dip-coating technique. The films as well as the dried powder of bulk gel were characterized by different techniques like X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM), atomic force microscope (AFM) and thermogravimetry–differential thermal analysis (TG–DTA). The hydrophilicity of the films was determined by measuring the water contact angles on the films. The results showed that the dopant of V₂O₅ on TiO₂ thin films could produce a visible-light response to the films, and the introduction of V₂O₅ could suppress the structural phase transition and crystal growth of TiO₂ crystal. Finally, the relationship between crystalline size and hydrophilicity under sunlight was investigated in this article.     

Effect of oxygen partial pressure on the growth of zinc micro and nanostructures

Zinc micro and nanostructures were synthesized in vacuum by condensing evaporated zinc on Si substrate at different gas pressures. The morphology of the grown Zn structures was found to be dependent on the oxygen partial pressure. Depending on oxygen partial pressure it varied from two-dimensional microdisks to one-dimensional nanowire. The morphology and structural properties of the grown micro and nanostructures were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Transmission electron microscopy (TEM) studies on the grown Zn nanowires have shown that they exhibit core/shell-like structures, where a thin ZnO layer forms the shell. A possible growth mechanism behind the formation of different micro and nanostructures has been proposed. In addition, we have synthesized ZnO nanocanal-like structures by annealing Zn nanowires in vacuum at 350 °C for 30 min.     

Growth and morphology of ruby crystals with unusual chromium concentration

Single crystals of ruby have been obtained from fluxed melts based on the systems Li₂O–MoO₃, Li₂O–WO₃, Na₂O–WO₃, 2PbO–3V₂O₅, PbO–V₂O₅–WO₃, PbF₂–Bi₂O₃ and Na₃AlF₆ by both the TSSG method and spontaneous crystallization at the temperatures 1330–900 °C. Al₂O₃ solubility has been measured for the flux composition of 2Bi₂O₃–5PbF₂ in the temperature range 1200–1000 °C and dissolution enthalpy has been defined as 29.4 KJ/Mol. The composition of grown crystals was studied by electron microprobe analysis. The synthetic ruby contains from 0.51 to 6.38 at% of chromium admixture depending on the crystal growth conditions. Experimental results on growth conditions, composition and morphology of grown crystals are presented for each flux and temperature interval.     

Combustion synthesis and luminescence properties of Dy-doped MgO nanocrystals

MgO nanocrystals doped with Dy³⁺ have been synthesized by a combustion method. The synthesized sample is characterized by X-ray diffraction, transmission electron micrograph, Fourier transform infrared, and photoluminescence spectroscopy. The as-prepared MgO nanocrystals appear to be single cubic crystalline phase and the diameter is in the range of 20–25 nm. The hypersensitive transition (⁴F_9/2→⁶H_13/2 of Dy³⁺) emission is prominent in the emission spectra resulting from the low-symmetry local site at which Dy³⁺ ions locate. In addition, the dependence of the luminescence intensity on Dy³⁺ concentration is also discussed.     

Resistivity distribution of silicon single crystals using codoping

Numerous studies including continuous Czochralski method and double crucible technique have been reported on the control of macroscopic axial resistivity distribution in bulk crystal growth. The simple codoping method for improving the productivity of silicon single-crystal growth by controlling axial specific resistivity distribution was proposed by Wang [Jpn. J. Appl. Phys. 43 (2004) 4079]. Wang [J. Crystal Growth 275 (2005) e73] demonstrated using numerical analysis and by experimental results that the axial specific resistivity distribution can be modified in melt growth of silicon crystals and relatively uniform profile is possible by B–P codoping method. In this work, the basic characteristic of 8 in silicon single crystal grown using codoping method is studied and whether proposed method has advantage for the silicon crystal growth is discussed.     

Growth of InAs on GaAs(1 0 0) by low-pressure metalorganic chemical vapor deposition employing in situ generated arsine radicals

InAs was grown by low-pressure metalorganic chemical vapor deposition on vicinal GaAs(1 0 0) substrates misoriented by 2° toward [0 0 1]. We observed InAs crystal growth, at substrate temperatures down to 300°C, employing in situ plasma-generated arsine radicals as the arsenic source. The in situ generated arsine was produced by placing solid arsenic downstream of a microwave driven hydrogen plasma. Trimethylindium (TMIn) feedstock carried by hydrogen gas was used as the indium source. The Arrhenius plot of InAs growth rate vs. reciprocal substrate temperature displayed an activation energy of 46.1 kcal/mol in the temperature range of 300–350°C. This measured activation energy value is very close to the energy necessary to remove the first methyl radical from the TMIn molecule, which has never been reported in prior InAs growth to the best of authors’ knowledge. The film growth mechanism is discussed. The crystallinity, infrared spectrum, electrical properties and impurity levels of grown InAs are also presented.     

Chemical vapor transport of zinc sulfide

Crystals of cubic zinc sulfide with different isotopic compositions have been grown by iodine vapor transport for basic research purposes (vibrational, electronic, and thermodynamic properties). The synthesis reaction in sulfur vapor was found to be controlled by solid-state diffusion of zinc atoms through a ZnS passivation layer. Crystals up to 5 mm in length were grown from small amounts of source material. The presence of argon reduced the nucleation density and favored the formation of facets.     

Growth of NaBi(WO4)2 crystal by modified-Bridgman method

NaBi(WO₄)₂ (NBW) crystals have been grown for the first time by modified-Bridgman method. Influences of some factors on the crystal growth process are discussed. X-ray powder diffraction experiments show that the unit cell parameters of NBW crystal are a=b=0.5284 nm, c=1.1517 nm, and V=0.3215 nm³. The differential thermal analysis shows that the NBW crystal melts at 923°C.     

Floating zone growth of high-quality SrTiO3 single crystals

Strontium titanate single crystals 15–20 mm in diameter and 40–80 mm in length were grown by a floating zone method with radiation heating. Additional crystal heating just below the molten zone by an in-growth annealing furnace was applied in order to lower the temperature gradients and to achieve slower cooling of the grown crystal. The crystal perfection was studied with X-ray topography and double-crystal diffractometry. The most perfect crystals were grown in [0 0 1] direction with single grain rocking curve widths of about 30″ and subgrain misorientations of 1′–3′ over 10×10 mm² areas of the boule cross-section for both (0 0 1)-, (1 1 0)- and (1 1 1)-oriented slices. Such high-quality crystal can be grown reproducibly with starting materials of 4N grade quality.     

Unidirectional seeded single crystal growth from solution of benzophenone

A novel crystal growth method has been established for the growth of single crystal with selective orientation at room temperature. Using volatile solvent, the saturated solution containing the material to be crystallized was taken in an ampoule and allowed to crystallize by slow solvent evaporation assisted with a ring heater. The orientation of the growing crystal was imposed by means of a seed fixed at the bottom of the ampoule. By selecting a suitable ring heater voltage and by controlling the ring heater voltage, nucleation and the growth rate of the crystal were controlled more effectively. By employing this novel method, benzophenone single crystal ingots of diameters 10 and 20 mm and length more than 50 mm were successfully grown using xylene as solvent. The ease in scaling up of diameter from 10 to 20 mm shows the vital advantage of this technique. It was possible to achieve solute–crystal conversion efficiency of 100 percent. The grown benzophenone crystal was characterized by FTIR, TG and DTA, powder X-ray diffraction, X-ray rocking curve, optical transmission study and powder SHG measurement. The results show that the crystal quality is at least as good as the quality of the crystal grown by other known methods. Also, microbial growth was naturally avoided in this method, as the fresh solution is constantly made available for the growing crystal.     

A room temperature solution-phase process to synthesize pure phase single-crystalline hexagonal cobalt hydroxide nanoplates

A simple room temperature solution-phase method has been developed to synthesize pure phase single-crystalline hexagonal β-Co(OH)₂ nanoplates. The chemical composition and morphology of the as-prepared β-Co(OH)₂ nanoplates were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The results indicated that the as-prepared β-Co(OH)₂ nanoplates were composed of pure brucite-like β-Co(OH)₂ phase with single-crystalline feature. The effect of polyethylene glycol (PEG), NH₄OH, and NaOH on the morphology and size of β-Co(OH)₂ nanocrystals were discussed in detail. The growth mechanism of the as-synthesized nanoplates was also discussed in detail based on the experimental results.     

Improved growth of PbI2 single crystals

The phase equilibrium and the crystallization process of lead iodide (PbI₂) melt have been primarily investigated according to the lead–iodine phase diagram. It is found that the iodine evaporation and the segregated lead deposition are the two important factors that affect the PbI₂ crystal quality. The new method of Pulling U-type quartz growth ampoule has been made to impede the decomposition of PbI₂ and the vaporization and condensation of iodine. An orange and translucent PbI₂ single crystal of large size was obtained by the improved growth method, i.e. U-type ampoule pulling. Resistivity of the as-grown crystal is up to 4×10¹¹ Ω cm, and IR transmission is up to 45% in the region from 7800 to 450 cm⁻¹. Therefore, the improved growth method is a promising convenient new method for the growth of high quality PbI₂ crystals.     

Facile and rapid synthesis of zinc oxalate nanowires and their decomposition into zinc oxide nanowires

We describe a simple etching route for the fabrication of zinc oxalate nanowires, which can be easily converted to zinc oxide nanowires by a simple decomposition process. The zinc oxalate nanowires can be obtained in restricted conditions, for example, when a zinc foil is immersed in ethanolic or propanolic oxalic acid. Interestingly, the nanowires are not obtained in aqueous, methanolic or butanolic oxalic acid. The solubility of zinc oxalate in the solvents and position of favorable precipitation are primarily responsible for determining the morphology of zinc oxalate.