Blue emission from arsenic doped gallium nitride

We have observed strong blue emission at room temperature from arsenic doped GaN samples grown by molecular beam epitaxy. Similar results were obtained for samples doped with both arsenic dimers and tetramers. The origin of this blue emission is discussed and a growth model proposed to account for our observations. We propose that arsenic doped GaN may be a suitable replacement for (InGa)N as the active region for blue light emitting devices.     

Shape evolution of zinc oxide from twinned disks to single spindles through solvothermal synthesis in binary solvents

Shape evolution of ZnO crystals from twinned disks to single spindles was studied through solvothermal synthesis in binary solvents N,N-diethylformamide (DEF) and methanol (MeOH). The MeOH content in DEF had large influence on the morphology of the obtained ZnO crystals. In MeOH-free DEF, well-shaped ZnO twinned disks with perfect mirror symmetry could be formed through the assembly of ZnO₄⁶⁻–julolidinium–ZnO₄⁶⁻ growth units on the (0 0 0 1) growth interfaces. For small amounts of MeOH (MeOH/DEF=0.04), elongated twinned disks were formed since the growth along the polar c-axis was enhanced. With increasing MeOH content (MeOH/DEF=0.1), twinned rods with reduced mirror symmetry were formed. When a large amount of MeOH was added to DEF (MeOH/DEF=0.5), single spindles rather than twinned disks or twinned rods were obtained. A similar shape evolution of zinc oxide was observed in binary solvents DEF and N,N-dimethylformamide (DMF), suggesting that the growth of ZnO crystals with tuneable shape and size can be controlled by the composition of the binary solvent mixture.     

Seed-mediated synthesis of uniform ZnO nanorods in the presence of polyethylene glycol

Large quantities of ZnO nanorods have been synthesized by the seed-mediated method in the presence of polyethylene glycol at 90 °C. The products are characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and high-resolution transmission electron microscopy. The as-grown ZnO nanorods are uniform with a diameter of 40–70 nm and length about 2 μm. The nanorods grew along the [0 0 1] direction. Possible roles of ZnO seeds and polymer in the growth of ZnO nanorods are also discussed.     

Growth of SiGe bulk crystals with uniform composition by utilizing feedback control system of the crystal–melt interface position for precise control of the growth temperature

We developed an automatic feedback control system of the crystal–melt interface position to keep the temperature at the interface constant during growth, and demonstrate its successful application to grow Ge-rich SiGe bulk crystals with uniform composition. In this system, the position of the crystal–melt interface was automatically detected by analyzing the images captured using in situ monitoring system based on charge-coupled-devices camera, and the pulling rate of the crucible was corrected at every 1 min. The system was found to be effective to keep the crystal–melt interface position during growth even when the variation of the growth rate is quite large. Especially, the interface position was kept for 470 h during growth of Ge-rich SiGe bulk crystal when we started with a long growth melt of 80 mm. As a result, a 23 mm-long Si_0.22Ge_0.78 bulk crystal with uniform composition was obtained thanks to the constancy of the growth temperature during growth through the control of the interface position. Our technique opens a possibility to put multicomponent bulk crystal in a practical use.     

Single crystal growth of copper phthalocyanine using exaltation–evaporation growth method

A new method of growing single crystal for β-form copper phthalocyanine (CuPc) is presented in this paper. Melted anthracene was used as solvent of CuPc. The method, vaporizing the solvent using an automatic exaltation machine, was employed to grow CuPc single crystals. The needle-like single crystals of CuPc up to 11.6 mm in length were obtained by applying this method. The influences of different temperatures, exaltation speeds and concentrations on the single crystals growth were also discussed. The method was called exaltation–evaporation growth method.     

Self-catalytic branch growth of SnO2 nanowire junctions

Multiple branched SnO₂ nanowire junctions have been synthesized by thermal evaporation of SnO powder. Their nanostructures were studied by transmission electron microscopy and field emission scanning electron microcopy. It was observed that Sn nanoparticles generated from decomposition of the SnO powder acted as self-catalysts to control the SnO₂ nanojunction growth. Orthorhombic SnO₂ was found as a dominate phase in nanojunction growth instead of rutile structure. The branches and stems of nanojunctions were found to be an epitaxial growth by electron diffraction analysis and high-resolution electron microscopy observation. The growth directions of the branched SnO₂ nanojunctions were along the orthorhombic [1 1 0] and . A self-catalytic vapor–liquid–solid growth mechanism is proposed to describe the growth process of the branched SnO₂ nanowire junctions.     

Growth of aragonite calcium carbonate nanorods in the biomimetic anodic aluminum oxide template

In this study, a biomimetic template was prepared and applied for growing calcium carbonate (CaCO₃) nanorods whose shape and polymorphism were controlled. A biomimetic template was prepared by adsorbing catalytic dipeptides into the pores of an anodic aluminum oxide (AAO) membrane. Using this peptide-adsorbed template, mineralization and aggregation of CaCO₃ was carried out to form large nanorods in the pores. The nanorods were aragonite and had a structure similar to nanoneedle assembly. This aragonite nanorod formation was driven by both the AAO template and catalytic function of dipeptides. The AAO membrane pores promoted generation of aragonite polymorph and guided nanorod formation by guiding the nanorod growth. The catalytic dipeptides promoted the aggregation and further dehydration of calcium species to form large nanorods. Functions of the AAO template and catalytic dipeptides were verified through several control experiments. This biomimetic approach makes possible the production of functional inorganic materials with controlled shapes and crystalline structures.     

Numerical study of induction heating in melt growth systems—Frequency selection

A set of 2D finite element numerical simulation of induction heating process for an oxide Czochralski crystal growth system has been made for a range of f=1–100 kHz applied frequency of driving current. It was shown that the frequency selection has a marked effect in all basic induction phenomena, including electromagnetic field distribution, skin depth, coil efficiency, and intensity and structure of heating in the growth setup.     

Hydrothermal crystal growth of fresnoite

The growth of fresnoite, Ba₂TiSi₂O₈, by hydrothermal synthesis has led to spontaneous generation of large, (4-5 mm) optically clear crystals from 6 M KF mineralizer solutions. Growth was achieved at relatively low synthesis temperatures (575 °C) comparative to fresnoite synthesis by Czochralski or flux methods. Bulk crystal growth possibilities were explored by transport reactions performed in both fluoride and hydroxide mineralizers with 25-45 °C temperature gradients. Growth rates of 0.14×0.19×0.22 mm³/week were established in 6 M KOH, which is significantly slower than standard hydrothermal rates of 1 mm/week. Although relatively slow, the hydrothermal method has been demonstrated as a synthesis route to high quality single crystals of fresnoite.     

Sublimation crystal growth of yttrium nitride

The sublimation–recombination crystal growth of bulk yttrium nitride crystals is reported. The YN source material was prepared by reacting yttrium metal with nitrogen at 1200 °C and 800 Torr total pressure. Crystals were produced by subliming this YN from the source zone, and recondensing it from the vapor as crystals at a lower temperature (by 50 °C). Crystals were grown from 2000 to 2100 °C and with a nitrogen pressure from 125 to 960 Torr. The highest rate was 9.64×10⁻⁵ mol/h (9.92 mg/h). The YN sublimation rate activation energy was 467.1±21.7 kJ/mol. Individual crystals up to 200 μm in dimension were prepared. X-ray diffraction confirmed that the crystals were rock salt YN, with a lattice constant of 4.88 Å. The YN crystals were unstable in air; they spontaneously converted to yttria (Y₂O₃) in 2–4 h. A small fraction of cubic yttria was detected in the XRD of a sample exposed to air for a limited time, while non-cubic yttria was detected in the Raman spectra for a sample exposed to air for more than 1 h.     

Surface growth mechanisms and structural faulting in the growth of large single and spherulitic titanosilicate ETS-4 crystals

Morphological, surface and crystallographic analyses of titanosilicate ETS-4 products, with diverse habits ranging from spherulitic particles composed of submicron crystallites to large single crystals, are presented. Pole figures revealed that crystal surfaces with a-, b- and c- axes corresponded to 110, 010 and 001 directions, respectively. Thus, technologically important 8-membered ring pores and titania chains in ETS-4 run along the b-axis of single crystals and terminate at the smallest crystal face. Height of the spiral growth steps observed on 1 0 0 and 0 0 1 surfaces corresponded to the interplanar spacings associated with their crystallographic orientation, and is equivalent to the thickness of building units that form the ETS-4 framework. Data suggest that the more viscous synthesis mixtures, with a large driving force for growth, increased the two- and three-dimensional nucleation, while limiting the transport of nutrients to the growth surface. These conditions increase the tendency for stacking fault formation on 1 0 0 surfaces and small angle branching, which eventually results in spherulitic growth. The growth of high quality ETS-4 single crystals (from less viscous synthesis mixtures) occurred at lower surface nucleation rates. Data suggest that these high quality, large crystals grew due to one-dimensional nucleation at spiral hillocks, and indicate that under these conditions un-faulted growth is preferred.     

Estimated effects of silicone glue on protein crystal growth

Silicone glue (modified silicone polymer) is widely used for both experiments involving inorganic crystal growth and those involving organic materials like proteins. This material is very useful for building a hand-made experiment setup or for fixing protein crystals to specific locations. Though silicone glue is regarded as harmful to proteins, no systematic verification was performed to investigate its impurity effects on protein crystal growth. We focused on and estimated the impurity effects of silicone glue on protein crystal growth.     

Solvothermal growth of ZnO

The growth of ZnO single crystals and crystalline films by solvothermal techniques is reviewed. Largest ZnO crystals of 3 inch in diameter are grown by a high-pressure medium-temperature hydrothermal process employing alkaline-metal mineralizer for solubility enhancement. Structural, thermal, optical and electrical properties, impurities and annealing effects as well as machining are discussed. Poly- and single-crystalline ZnO films are fabricated from aqueous and non-aqueous solutions on a variety of substrates like glass, (100) silicon, -Al₂O₃, Mg₂AlO₄, ScAlMgO₄, ZnO and even some plastics at temperatures as low as 50 °C and ambient air conditions. Film thickness from a few nanometers up to some tens of micrometers is achieved. Lateral epitaxial overgrowth of thick ZnO films on Mg₂AlO₄ from aqueous solution at 90 °C was recently developed. The best crystallinity with a full-width half-maximum from the (0002) reflection of 26 arcsec has been obtained by liquid phase epitaxy employing alkaline-metal chlorides as solvent. Doping behavior (Cu, Ga, In, Ge) and the formation of solid solutions with MgO and CdO are reported. Photoluminescence and radioluminescence are discussed.     

Low-temperature growth of ZnO with controllable shapes and band gaps

By using polyvinylpyrrolidone (PVP) as the nucleation promoter and directing agent, the shape-selective synthesis of ZnO has been realized at 35 °C. By simply modifying the amount of PVP or/and water, the product shape can be readily changed from one-dimensional structure via monolayer and semi-bilayer to bilayer structure with controlled aspect ratio (defined as monolayer thickness/edge length). As shown by both the photoluminescence and absorption spectra, the ZnO band gap can be modified by adjusting the sample shape. The low-temperature route reported here should open an effective and low-cost approach to the ZnO with tunable shapes and band gaps.     

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).     

Bridgman growth and site occupation in LuAG:Ce scintillator crystals

LuAG:Ce single crystals with various activator concentrations were grown by the vertical Bridgman technique. Characterization of crystals was done in terms of actual doping level, macroscopic defects and degree of non-equivalent substitutions by Lu for Al in octahedral lattice sites. Scintillation measurements were performed using 2×2×8 mm³ shaped samples with Ce concentration in the range 0.05–0.55 at%. Essential improvement of performance was demonstrated in samples containing ≥0.2 at% of Ce; the light yield measured in LuAG:Ce (0.55 at%) was about 26000 ph/MeV, or close to that of LSO.     

Nucleation, growth and characterization of L-tartaric acid—nicotinamide NLO crystals

The solubility, metastable zone width and nucleation parameters of organic nonlinear optical material L-tartaric acid–nicotinamide (LTN) have been determined. The crystals of LTN are grown by the slow cooling method. The grown crystals are morphologically interpreted. The crystalline powder of the grown crystals has been examined by X-ray diffraction and thermogravimetric analysis. The different modes of vibrations present in the crystal are identified by the Fourier infrared spectroscopy analysis. The powder SHG efficiency of LTN is comparable with that of KDP.     

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.     

Deposition of bulk GaN from solution in gallium under high N2 pressure on silicon carbide and sapphire substrates

Results of high-pressure directional growth of GaN on foreign substrates: SiC, sapphire and GaN/sapphire MOCVD templates are presented. The role of nitrogen pressure and supersaturation in the growth process is discussed. The conditions for stable growth of the nitride are determined. The results of the crystallization process are compared with those obtained for directional growth on pressure grown GaN crystals.