Growth of hollow Se–Te whisker crystals

On the basis of micro- and macro-morphological studies the mechanism responsible for the growth of Se–Te whiskers has been suggested. It has been shown that Sc–Te whiskers grow by layer growth mechanism in which screw dislocation is not the source of step but the growth proceeds by two-dimensional nucleation. This has been supported by the supersaturation data. The plausible mechanism for the growth of hollow whiskers has also been suggested.     

Effect of added carbon black on iron whisker growth

As previously reported, mass-growth of iron whiskers can be achieved by reduction of halide admixed with carbon black. In order to investigate the role of added carbon black on iron whisker growth, the growth rates and morphology have been investigated. It was found that the effect is related to an adsorption process at the tip growth sites which are limiting the reaction. The heat of adsorption of the halide increases and markedly multi-nucleous growth and large growth rates appear on many whiskers. There is no effect of carbon black below 500°C since the vapor pressure of the adsorbed halide is small.     

MOVPE growth of single-crystal hexagonal AlN on cubic diamond

We have obtained single-crystal aluminum nitride (AlN) layers on diamond (1 1 1) substrates by metalorganic vapor-phase epitaxy (MOVPE). When the thermal cleaning temperature of the substrate and growth temperature of the AlN layer were below 1100 °C, the AlN layer had multi-domain structures mainly consisting of rotated domains. An interface layer, consisting of amorphous carbon and poly-crystal AlN, was formed between the AlN layer and the diamond substrate. On the other hand, when the thermal cleaning temperature and growth temperature were above 1200 °C, a single-crystal AlN layer was grown and no interface layer was formed. Therefore, we attribute the multi-domain structures to the interface layer. Even at the growth temperature of 1100 °C, by performing the thermal cleaning at 1200 °C, the single-crystal AlN layer was obtained, indicating that the thermal cleaning temperature of the substrate is a critical factor for the formation of the interface layer. The epitaxial relationship between the single-crystal AlN layer and the diamond (1 1 1) substrate was determined to be [0 0 0 1]_AlN∥[1 1 1]_diamond and [1 0 1¯ 0]_AlN∥[1 1¯ 0]_diamond. The AlN surface had Al polarity and no inversion domains were observed in the AlN layer.     

Controllable fabrication and growth mechanism of hematite cubes

Monodispersed and single‐crystalline hematite (α‐Fe₂O₃) cubes have been successfully prepared by a template‐free hydrothermal synthetic route with FeCl₃ and CH₃COONH₄. The influences of the reactant concentration, reaction temperature, and reaction time on the crystal growth were systematically investigated. The results show that the monodisperse hematite cubes with high crystalline and narrow size distribution could be fabricated at the hydrothermal temperature of 160 °C for 24 h while the concentrations of FeCl₃ and CH₃COONH₄ were in the range of 0.03‐0.5 M and 0.05‐0.1 M, respectively. In addition, the formation mechanism of hematite cube is also proposed, where the CH₃COONH₄ plays a role of shape controller in the formation of cube hematite structure. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Controlled growth of Ti4O7 crystals by chemical transport reactions

Ti₄O₇ is a striking example of the difficulties involved in the simultaneous control of crystal growth and composition. In this respect, the usual back-transport step must be avoided because it results to the formation of mixed phases. However, an appropriate H₂ heat treatment can reduce these mixed crystals into single phase single crystals. This result is ascertained by accurate and sensitive physical methods. Finally suitable pulling transport experiments lead to the growth of centimeter long crystals.     

Dendritic growth of snow crystals

The hypothesis that allows the interpretation of dendritic growth of a snow crystal in terms of diffusion-limited aggregation is criticized. The results of simulation of growth of quasi-two-dimensional crystals in two-and three-dimensional media based on the classical two-parametric model of diffusion-limited aggregation are used as an argument in this criticism. It is established that the model dimensionality considerably influences morphology of the grown crystal. The mechanism of dendritic growth of a snow crystal in which the main part is played by the surface processes at the ice/water interface is suggested.     

Iso-epitaxial growth of n-octacosane crystals

Iso-epitaxial(epilayer)growth of n-octacosane crystals is reported. The morphology of the epilayers is in the form of triangular growth islands with or without truncature. Epilayer growth precedes spiral growth mechanism which occurs at medium and low supersaturations, respectively. The occurrence of triangular and truncated rhombic platelets is found to be a manifestation of growth at medium supersaturations.     

Controlled synthesis of SrCrO4 crystals with different morphologies

Rod‐shape, branch‐shape, bouquet‐shape and claw‐shape SrCrO₄ crystals were synthesized through biomembrane/organic‐addition supramolecular templates. The shapes are mainly changed with variance of the organic reagents and organic membranes. Most of the morphologies haven't been reported in the literature. This method may meet with the requirements to synthesize materials of various morphologies and size by using different supramolecular templates. This paper discusses how to control crystals' growth by supramolecular templates. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spiral growth of potassium bichromate crystals

Some observations of growth spirals and hillocks on {001} surfaces of potassium bichromate crystals grown from aqueous solutions are presented and discussed. It is shown that a spiral pattern in fact represents a macrospiral developed as a result of the cooperative action of a group of dislocations.     

The growth of HgI2 crystals

The paper presents a system for αHgI₂ crystal growth by the temperature oscillation method. The system has a capability of crystal growing at an excess I₂ or Hg vapour pressure. Optimum conditions for producing crystals up to 2 cm³ by volume have been established. The crystals grown at an excess I₂ vapour pressure have higher resistivity and higher drift electron and hole mobilities — μ_e = 120 cm² V⁻¹ s⁻¹ and μ_h = 6 cm² V⁻¹ s⁻¹, respectively.     

Preferred growth of bismuth single crystals

The results of the study of the factors influencing the orientation of the ( 111 ) cleavage plane of bismuth are presented. It has been observed that at high purity the growth rates and temperature gradients do influence the orientation whereas at low purities no such influence is observed.     

Dendritic growth forms of borax crystals

A variety of dendritic forms of borax grown from solutions by the film formation method is given. The changing growth morphology is followed as a function of concentration and temperature. The initial, intermediate and final growth morphologies are described and discussed. Influence of evaporation rate and supersaturation on the mechanism of growth is assessed. It is suggested that under all crystallization conditions, borax crystals have dendritic form in the initial stages of growth.     

Solid-phase growth of CuGaS2 crystals

Homogenized mixtures of copper, gallium, and sulphur were annealed for 200 hrs. under vacuum at about 1000–1050°C (i.e. below the melting point of the CuGaS₂ phase) in quartz ampoules in a vertical position, and then cooled down in a temperature gradient. The final charge was made up of three well-defined portions: a yellow polycrystalline CuGaS₂ with large blocks of CuGaS₂ (close to stoichiometry), a black portion with darkgreen aggregates of small CuGaS₂ crystals, and yellow laminae of CuGaS₂ single crystals, slightly inclined away from [112] direction. — A coupled growth mechanism — solidstate-diffusion-assisted coalescence/vapour transport — is assumed.     

Curie symmetry principle and growth of single crystals

Application of the symmetry principle, proposed by Pierre Curie, to the growth of single crystals is considered. The basic concepts of this principle and the rules for alignment of the crystallographic symmetry of a seed crystal with the external symmetry of the thermal field formed by the crucible with a melt are shown. The modified Stepanov method, developed at the General Physics Institute, Russian Academy of Sciences, on the basis of the Czochralski and Stepanov methods, is described, and its advantages are demonstrated. Examples of application of this technique to the growth of complex oxide crystals are given.     

Pinacoidal growth and optical properties of calcite crystals

Optical quality calcite single crystals, CaCO₃, have been grown under hydrothermal conditions in the of CaCO₃ - NH₄Br - H₂O system doped with Li ions. 24- liter autoclaves including titanium inserts were used in these experiments. Optical properties of calcite crystals were studied. The light absorption index of the crystals grown is similar to rhombohedron materials, but pinacoidai calcite have no V-shaped defects.     

Vapour growth and morphology of PbBr2 crystals

In this paper, the vapour transport of PbBr₂ under vacuum during vacuum distillation refining and its condensation on the wall of the vessel were described. The macro‐ and micro morphologies of PbBr₂ crystals grown in the vessel (glass tube) were studied. The crystal shape changed dramatically depending on the positions of condensation in the vessel, i.e., the crystal shape varied from an isometric polyhedron to columnar crystals with facets, and to a massive crystal without facets with a rise in the wall temperature. These results were interpreted in terms of the concentration gradient of the molecules in the vessel, surface roughening and/or surface melting of the crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of anions on rapid growth and growth habit of KDP crystals

The synthesis of KDP from its raw material has been found exist in the growth solution. In the crystal growth experiment, significant extension of specific faces was observed at low dopant concentration. At high doping concentration, the growth rate of the whole crystal decreased with no significant habit modification. The inhibiting effects of phosphite and other H-bonding anionic ions on the growth of pyramidal faces are discussed. Rapid growth rate experiments have been carried out with purified material and an averaged growth rate of 18.6mm/day was obtained.     

Vapour growth and epitaxy of minerals and synthetic crystals

Surface microtopographs of the following crystals, both natural and synthetic, grown from pure vapour phase (PV), by chemical vapour transport (CVT), from high temperature solution (HTS) and hydrothermal solution (HS) are compared according to the criteria of (1) whether spirals are circular or polygonal and (2) how wide is the step separation of the spiral; SiC (PV, CVT, both synthetic), hematite (CVT, HTS, natural and synthetic), corundum (CVT, HTS, synthetic), mica minerals (PV, CVT, HS, natural and synthetic) and beryl (CVT, HTS, HS, natural and synthetic). Clear differences in morphology and step separation were found between crystals grown from vapour phase and solutions, between PV and CVT, as well as between natural and synthetic crystals. The differences are analysed in conjunction with the recent developments of computer simulations on spiral morphology. The results show interaction between solid and fluid plays very important role in determining the spiral morphology. Oriented intergrowth between different crystals well known among minerals, such as epitaxy, topotaxy, co-axial intergrowth, exsolution etc. are briefly summarized. It is also briefly explained how these relations are used in understand the growth or cooling histories of natural minerals.     

Hydrothermal growth of crystals under visual examination

Hydrothermal growth, recrystallization and synthesis of -TeO₂. Te₆O₁₁C₁₂, CuBr, PbI₂, PbBr₂, PbCl₂ SbNbO₄ monocrystals in an apparatus with visual examination are considered. In the apparatus with an optical quartz reactor the experiments were carried out to study the hydrodynamics of the solution in the homogenous and binary phase gas-liquid media. The data obtained agree well with those calculated thus permitting us to take into account the effect of hydrodynamical environment on supersaturation and mass transport kinetics. This fact was demonstrated while studying kinetics of mass transport of -TeO₂ on seeds in homogenous and binary phase gas liquid media. Solubility of TeO₂ monocrystals and kinetic properties of their growth were studied in their dependences on physical, chemical and hydrodynamical parameters and the growth mechanism was suggested. Simultaneous growth of tellurium dioxide and oxychloride monocrystals was first observed in the system TeO₂-HCl-H₂O in homogenous and binary phase solutions, the corresponding dependences on temperature, temperature gradient and HCl concentration have been analyzed. The mechanism of simultaneous growth of these crystals and its relationship with the composition of the crystallization medium are considered. The apparatus with visual examination was demonstrated to be useful in the synthesis and recrystallization of PbHal (Hal = I, Br, Cl) monocrystals under various PT conditions.     

Horizontal bridgman growth of gaas single crystals

In order to meet requirements for the preparation of low dislocation density GaAs single crystals a horizontal Bridgman type apparatus was designed. Construction of the apparatus allows the establishment of enhanced temperature stability of the arsenic source and hence better stability of the arsenic vapour pressure during the growth. This effect was achieved without application of heat pipes which are usually used for the improvement of thermal profile and temperature stability. The influence of different arsenic vapour pressures on the density of dislocations was confirmed in the course of this work.