Habit modification and improvement in properties of potassium hydrogen phthalate (KAP) crystals doped with metal ions

Potassium hydrogen phthalate (KAP) single crystals were grown by slow evaporation and slow cooling techniques. The growth procedure like temperature cooling rate, evaporation rate, solution pH, concentration of the solute, supersaturation ratio etc., has been varied to have optically transparent crystals. Efforts were made to dope the KAP crystals with rubidium, sodium and lithium ions. The dopant concentration has been varied from 0.01 to 10 mole percent. Good quality single crystals were grown with different concentrations of dopants in the mother phase. Depending on the concentration of the dopants and the solution pH value, there is modification of habit. Rubidium ions very much improve the growth on the prismatic faces. The transparency of the crystals is improved with rubidium and sodium doping. The role of the dopants on the non‐linear optical performance of KAP indicates better efficiency for doped crystals. The grown crystals were characterized with XRD, FT‐IR, chemical etching, Vickers microhardness and SHG measurements. The influence of the dopants on the optical, chemical, structural, mechanical and other properties of the KAP crystals was analysed. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Synthesis,bulk growth,polarizability and nonlinear optical properties of γ‐glycine single crystals

The role of sodium acetate, sodium nitrate, sodium hydroxide and malonic acid as additives in assisting the nucleation of γ‐polymorph from solution has been investigated. For the first time large dimensional bulk single crystals of γ‐glycine have been grown at the optimized concentration of the additives by the top seeded slow cooling technique. The bulk growth of single crystals elucidates well the unidirectional growth characteristics and the existence of merohedral twinning in γ‐ glycine. Polarizability, plasmon energy and Fermi energy has been evaluated for the first time for γ‐glycine single crystals based on an analytical approach. Structural affirmation of the nucleated polymorph has been carried out by Powder x‐ray diffraction and the thermal characteristics of the nucleated polymorph are well revealed by Differential Scanning Calorimetry. The non linear optical characteristics of γ‐glycine studied by Kurtz and Perry technique revealed increased SHG efficiency with the highest of about 2.2 in the presence of malonic acid compared to the standard Potassium dihydrogen orthophosphate (KDP).     

A Study on Carbon Incorporation in Semi‐Insulating GaAs Crystals Grown by the Vapor Pressure Controlled Czochralski Technique (VCz) Part I: Experiments and Results

In the past it has been demonstrated that the carbon concentration of large semi‐insulating (SI) GaAs single crystals grown by the conventional liquid encapsulation Czochralski (LEC) technique can be controlled by several methods including variations of growth parameters. It was the aim of the present paper to clarify which of the relationships of LEC growth could be used for a carbon control in the VCz‐method characterized by the application of an inner chamber made from graphite to avoid selective As evaporation. In detail this comprised a study of the influence of several growth parameters like the water content of the boric oxide, the composition of the working atmosphere, the gas flow, a titanium gettering and additions of gallium oxide. As a result, for the first time carbon concentrations down to ≈ 1014 cm^‐3 were obtained in 3'' (75 mm) diameter VCz crystals.     

Surface structures of fluorite crystals

Optical studies have been made of the microstructures on the natural {100} and {111} faces of natural fluorite crystals. The protrudance of triangular elevations, growth pyramids, and natural etch pits have been observed on a large number of crystals. It is suggested that fluorite crystals grown by two-dimensional spreading and piling of growth layers parallel to {100} faces. The natural etch pits on {100} and {111} faces suggest that they have been produced as a result of a dissolution process in nature. The natural faces have been etched in the laboratory and it is established that the pits indicate the existence of linear defects in the crystals. The implications are discussed.     

Solidification behaviour of organic nonlinear optical crystals

A representative rather than exhaustive review has been given on the solidification behaviour of organic nonlinear optical crystals. Many of the developments reported here represent quick experimental responses to the rapid theoretical advances made in the field of nonlinear optics. The article is divided into four parts. The first part deals with the characteristics of the organic nonlinear materials and need for large single crystals. The second and third parts are devoted to the thermophysical properties and experimental studies on crystallization processes. Here, recent work by authors is reviewed on the purification of source material, solidification behaviour and crystal growth. Various interactions between morphology, microsegregation, defects, growth velocity and temperature gradient are discussed. Specific examples of substituted anilines are presented. In the fourth section a stronger interaction is suggested between optical physicists and crystal growers to understand the problems of inhomogeneity, stress, damage threshold and doping in the organic crystals.     

Understanding the growth mechanism of CuI crystals during gel growth experiments

Cuprous iodide crystals have been grown with decomplexation method in silica gel. Various crystal morphologies, such as polycrystalline aggregate, skeletal, dendrite, hopper crystals and regular tetrahedron crystals, were observed in different growth regions with an optical microscope. Their surfaces were photographed using a binocular metallographic microscope and the results were explained with the crystal growth mechanism which was determined by supersaturation. These observations support the general hypothesis that the concentration of reactant affects the relative growth rate by controlling the nucleation and diffusion. The mutual influence of the crystals grown in different regions was also discussed. Additionally, the suitable condition for getting regular tetrahedron crystals or large hopper crystals was obtained by changing the concentration of CuI·HI complex in the later period of crystal growth. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Observations on the growth of NiMoO4 crystals in Silica gel media

Growth of NiMoO₄ crystals by gel method has been described. By manipulating the condition of growth parameters, crystals of fairly large dimensions have been obtained at ambient temperature. The crystal faces are examined by optical and scanning electron microscopy and thus a two-dimensional layer growth mechanism for the development of the faces have been proposed.     

基于钠助熔剂法的GaN单晶生长研究进展

宽禁带氮化镓(GaN)材料以其独特的性质和应用前景成为国内外研究的热点,高质量GaN单晶衬底的制备是获得性能优异的光电子器件和功率器件的基础。钠助熔剂法生长条件温和,易获得高质量、大尺寸的GaN单晶,是一种具有广阔商业化前景的GaN单晶生长方法。钠助熔剂法自20世纪90年代末期被发明以来,经过20多年的发展,钠助熔剂法生长的晶体在尺寸与质量上都取得了长足的进步。本文从晶体生长原理和关键工艺(籽晶选择、温度梯度以及添加剂)等方面综述了钠助熔剂法生长GaN单晶研究进展,并对其面临的挑战和未来发展趋势进行了展望。     

Growth and microscopic studies of yttrium aluminium garnet single crystals

A study has been made to understand the growth history and growth mechanism of flux grown yttrium aluminium garnet (YAG) single crystals. Etching has been done to reveal the growth patterns of flux grown crystals. Optical and scanning electron micrographs are presented. Optical micrographs were taken under polarised light and oblique incident light. The nature and origin of growth hillock is elucidated.     

Growth of large single crystals of stearic acid from solution

The growing of large single crystals of stearic acid (CH₃(CH₂)₁₆COOH), one of the saturated fatty acids, from organic solutions is reported. There are two parts in this experimental investigation; (1) to clarify the relationship between polymorphism of stearic acid having three modifications, namely, the A-form (orthorhombic), the B- and C-forms (monoclinic) and the growth conditions in the case of solution growth, because this complicated relationship has apparently made it very difficult to obtain large single crystals, (2) to produce large single crystals of stearic acid under the optimum growth conditions according to part (1). As a result large single crystals of stearic acid more than 8 × 8 mm² in area of the B- and C-modifications were successfully obtained. The values of long spacing, the crystal habit and the cleavage plane are also reported.     

PVT and CVT Growth and Characterization of SnSxSe2-x (0 ≤ x ≤ 2) Single Crystals

Single crystals of solid solutions of tin sulphoselenide have been grown in the same ampoule. Specific conditions for growing single crystals of SnSSe have also been identified. A study of microstructures on the growth surfaces responds to the mechanism of growth of these crystals. The dependence of electrical resistivity, Hall mobility and carrier concentration with the values of the configuration parameter 2 has been studied.     

Microstructures of gel-grown ammonium hydrogen tartrate single crystals

Single crystals of ammonium hydrogen tartrate (AHT) have been grown in silica gels by employing the controlled reaction between ammonium chloride and tartaric acid. Transparent AHT crystals upto 24 × 4 × 3 mm³ in size have been grown at room temperature. Optical and electron-optical studies have been made on the various surface structures of {010} faces of the grown crystals. A variety of growth striations and growth hillocks have been observed. Growth layers modified by the presence of misaligned microcrystals have been illustrated. It has been suggested that two-dimensional nucleation, spreading and pilling up of growth layers is mainly responsible for the growth of these crystals and the implications are discussed.     

Advances on potential-driven growth of metal crystals from ionic liquids

This article highlights the electrodeposition of metals, in crystalline or amorphous form, that are monentous in the present era of science and technology. Available literature related to nucleation and growth of metal crystals has been reviewed to gain insight into the mechanism and kinetics. The progress made in the electrodeposition technique, using an ionic liquid (IL) medium, has been detailed for selected metals using different ILs for achieving the controlled growth mechanism driven by electrochemical potential. Theoretical models for nucleation and growth of crystals by electrodeposition have been explained and the effect of crystallization overpotential on the growth of crystal growth has been discussed. Finally, the factors affecting the growth process and the mechanism have been identified and critically analyzed based on the available literature, fundamental knowledge-base, chemistry of ILs, and electrodeposition.     

Microstructures on {111} faces of stannic iodide single crystals

Single crystals of stannic iodide (SnI₄) havebeen grown using the controlled reaction between SnCl₂ and KI by diffusion process in silica gel medium. Orange to reddish octahedral stannic iodide crystals up to 3–4 mm in size have been grown at room temperature. Optical studies have been made on the various surface structures of {111} faces of the asgrown crystals. On octahedral faces of these crystals, triangular-shaped hillocks with growth layers in the 〈110〉 directions have been observed. Occasionally, growth spirals on octahedral faces have also been reported. Close loops of growth fronts have been investigated and have been interpreted. It has been suggested that two-diemensional nucleation, spreading and pilling up of triangular growth layers is mainly responsible for the growth and occasionally the growth is due to screw dislocations. The implications are discussed.     

PVT and CVT Growth and Characterization of SnSxSe2-x (0 ⩽ <x 2) Single Crystals

Single crystals of solid solutions of tin sulphoselenide have been grown in the same ampoule. Specific conditions for growing single crystals of SnSSe have also been identified. A study of microstructures on the growth surfaces responds to the mechanism of growth of these crystals. The dependence of electrical resistivity, Hall mobility, carrier concentration with the values of the configuration parameter x has been studied.     

An electrolytic method to grow copper dendrites and single crystals in gels

A new electrolytic method for the growth of any metallic crystal in gel by using gel as a medium for controlled growth, is reported. Different types of large dendrites and single crystals of copper were grown by electrolytic method in the gel medium. It is found that pH of the gel medium, the concentration of the supernatant solution, the current density and the electrode material used, have considerable influence on the habits of the dendrites and the single crystals thus grown. The surface features and morphology of crystals and dendrites were studied by optical and scanning electron microscopy. Compared to other conventional electrolytic growth techniques, the present method has a number of additional parameters that can be varied, and hence a more effective controlled growth of crystals is possible.     

Optimization of the Growth Technology for Crystals with Garnet Structure Based on X-Ray Diffraction Data

High efficiency of the methods of double-crystal X-ray diffractometry (DCXRD) and topography for improving the growth technology of highly homogeneous crystals has been demonstrated on the example of gadolinium gallium garnet (GGG) single crystals. The main types of structural defects observed in Czochralski-grown GGG crystals are found to be macroscopic inhomogeneity of composition distribution, caused by the facet effect manifestation; microinhomogeneous distribution of impurity and main components of the composition in striations; dislocations; and second-phase inclusions. The relationship between the type and density of newly formed defects and the technological conditions for crystal growth are considered. Optimization of the composition of crystals and their growth technology made it possible to obtain high-quality dislocation-free crystals of GGG and complex-substituted garnets on its basis for magneto-optical and microwave devices, elements of solid-state lasers, and other applications.     

Characterization of bismuth germanate crystals grown by EFG method

Bismuth germanate shaped crystals have been grown by the EFG (Stepanov) method. The correlation between growth rate, shape of crystals, their optical and scintillation parameters has been analysed. Optical and scintillation characteristics of the EFG crystals are similar to those obtained with Czochralski grown crystals, however, growth rate in EFG is by 2.5 times larger. Also we compare the photochromic effect under UV‐irradiation in EFG and Czochralski grown crystals. Material losses at fabrication of plates, pixels, and rods from EFG shaped plates may be reduced by ∼50% compared to large diameter boules.     

Doping of GaSb single crystals with volatile elements

The Czochralski technique without encapsulant in a flowing atmosphere of hydrogen was used for the growth of GaSb single crystals doped with either sulphur or nitrogen. It has been shown that this method is not suitable for the prepartion of GaSb doped with volatile elements because they evaporate during the growth procedure and impair the single crystalline growth. The highest concentration of sulphur in the single crystals has been found to be < 1.2 × 10¹⁷ atoms · cm⁻³. At higher concentrations, GaSb became either polycrystalline or twinned. The growth of N-doped single crystals was similar to that of S-doped GaSb.