Growth kinetics of CaF2 in a pH-stat fluidized-bed crystallizer

In this study, experiments were first conducted in a stirred vessel to establish the metastable region of calcium fluoride, using a pH-stat apparatus for controlling the pH value of solution. The effects of pH value on the solubility and metastable region were observed. Then, operating variables, including supersaturation, superficial velocity, pH value, seed size, and types of seed and solution, that influenced the crystal growth of the same system were investigated in a fluidized-bed crystallizer. The crystal growth rates were determined from the consumption rates of fluoride ions. The growth kinetics was explored by using the two-step growth model. The effectiveness factor was used to judge whether a controlling step was existing. The kinetics of crystal growth in a lean bed and a dense bed was also discussed.     

Influence of trivalent ions codoping on the Mo:PbWO4 luminescence properties

Trivalent ions codoping Mo:PWO boules were grown along the c-axis using the Czochralski technique. Trivalent ions codoping improved the fast components of luminescence for Mo:PWO due to suppression/compensation of hole-trapping centers. Correspondingly, trivalent ions codoping increased the fast components of the light yield. The La³⁺ and Gd³⁺ concentration in the crystal gradually decreased along the growth direction because they increased the melting point. The Y³⁺ concentration increased along this direction due to the different influence on the melting point. Compared with La:Mo:PWO, Y:Mo:PWO shows a more uniform transmittance along the growth direction.     

A statistical thermodynamic model for oxygen segregation during Czochralski growth of silicon single crystals

A thermodynamic model derived from atomic scale statistics is formulated for the crystal–melt interface where oxygen segregation occurs during silicon crystal growth by the Czochralski method. The model shows that the segregation coefficient is close to but less than unity. Approaches for controlling oxygen concentration in the resulted crystal are discussed.     

Mathematical modeling of grown-in defects formation in Czochralski silicon

On the basis of a mathematical model proposed previously [S. Kobayashi, J. Crystal Growth 174 (1997) 163], oxygen precipitation in growing Czochralski (CZ) crystals is analyzed, and the calculated results are compared with experimental data of grown-in defects observed with laser scattering tomography (LST). The behavior of oxygen precipitates is qualitatively very similar to that of grown-in defects, but there are quantitative discrepancies between the calculation and the observation. The formation process of grown-in defects is discussed.     

Experiments on the oscillatory convection of low Prandtl number liquid in Czochralski configuration for crystal growth with cusp magnetic field

This paper presents results of experiments on the oscillatory convection of mercury in a Czochralski configuration with cusp magnetic field. Temperature fluctuation measurements are carried out to determine the critical Rayleigh number for the onset of time dependent natural convection. The effects of a cusp magnetic field on the supercritical natural convection coupled with rotation of crystal disk are investigated. In the presence of a rotating flow it is found that a cusp magnetic field can induce a new long wave instability and can amplify the temperature fluctuation depending on the magnitude of the relevant flow similarity parameters and the melt aspect ratios. A flow regime diagram for the amplification and damping of the temperature fluctuations is presented to provide an experimental data base for finding optimum growth conditions in the cusp magnetic field Czochralski process.     

Influence of Coriolis force on thermal convection and impurity segregation during crystal growth under microgravity

In contrast with the generally accepted viewpoint, it is shown that the Coriolis force caused by rotation of an orbital station can appreciably affect natural convection and impurity distribution during the growth of crystals from a melt in orbital flight conditions. 2D and 3D steady and oscillatory convection in a rectangular enclosure is considered. The resonance phenomenon arising due to the interaction of the Coriolis force and harmonic oscillations of the gravity force is demonstrated. It is shown that for moderate values of the Ekman number the Coriolis force suppresses convection in one direction and amplifies it in the other, which in turn results in deformation of the impurity distribution over the cross-section of the crystal.     

Low-temperature fabrication and photocatalytic activity of clustered TiO2 particles formed on glass fibers

Clustered anatase phase TiO₂ particles were uniformly formed on the surface of glass fibers by a liquid phase deposition (LPD) method at 60 °C using TiF₄ and H₃BO₃ as the precursors. The clustered TiO₂ particles deposited on the glass fibers and as a photocatalyst these particles not only have a larger surface area than TiO₂ thin films, but also can avoid the disadvantages of using TiO₂ powders encountered in air purification or water treatment. The photocatalytic activity of the sample was evaluated by the photocatalytic oxidation of nitrogen monoxide (NO) in the gaseous phase. The deposition conditions and chemical composition of the clustered TiO₂ particles were discussed. It was found that the clustered TiO₂ particles that formed on the glass fibers obviously showed photocatalytic activity without high-temperature calcination. A formation mechanism was proposed to account for the formation of TiO₂ clustered morphology on the glass fibers.     

Selective-controlled synthesis of one-dimensional strontium phosphates

Anorthic SrHPO₄ nanobelts and hexagonal Sr₁₀O(PO₄)₆ nanorods were obtained by a simple hydrothermal method without adding any surfactant as template. The as-synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). TEM and HRTEM observations of the products revealed that the as-prepared SrHPO₄ nanobelts and Sr₁₀O(PO₄)₆ hexagonal nanorods are single crystals with their preferential growth direction along the normal of (1 0 0) and (0 0 1) planes, respectively.     

Selective epitaxy and lateral overgrowth of 3C-SiC on Si – A review

This review article attempts to present a comprehensive picture of the progress in selective epitaxial growth (SEG) of cubic silicon carbide (3C-SiC) to make it a cheap and practical material for high temperature and high power, high frequency and MEMS (Micro Electromechanical Systems) applications. Selective epitaxial growth followed by epitaxial lateral overgrowth (ELO) is a suitable approach to minimize the interfacial defects and other planar defects in case of thin film growth. Different techniques of SEG and its application to Si, GaAs and III–V nitrides are reviewed briefly in the first section of this article. Various SEG techniques like epitaxial lateral overgrowth, pyramidal growth and pendeo epitaxial growth, etc. have been discussed extensively for growing 3C-SiC on Si, together with the characterization of the grown films. The influence of various experimental parameters such as temperature of growth, choice of mask material, influence of an etchant, pattern shape and size, etc. is also discussed. On the basis of these data, it is believed that SEG and related techniques are a promising approach for heteroepitaxial growth of 3C-SiC films useful for devices and MEMS applications.     

The influences of supersaturation on LPE growth of GaN single crystals using the Na flux method

The dependency of LPE growth rate and dislocation density on supersaturation in the growth of GaN single crystals in the Na flux was investigated. When the growth rate was low during the growth of GaN at a small value of supersaturation, the dislocation density was much lower compared with that of a substrate grown by the Metal Organic Chemical Vapor Deposition method (MOCVD). In contrast, when the growth rate of GaN was high at a large value of supersaturation, the crystal was hopper including a large number of dislocations. The relationship between the growth conditions and the crystal color in GaN single crystals grown in Na flux was also investigated. When at 800 °C the nitrogen concentration in Na–Ga melt was low, the grown crystals were always tinted black. When the nitrogen concentration at 850 °C was high, transparent crystals could be grown.