Growth of low dislocation density single crystals of nickel

Low dislocation density single crystals of nickel have been grown at high ambient pressure by the Czochralski method. X-ray Laue picture shows that the crystals are strain-free. The dislocation density was determined to be <10³/cm² by the etching procedure. It was found that the necking and cone regions are very critical in the dislocation introduction in the crystals. An increase in the ambient pressure used during the growth seems to aid the crystal quality.     

Defect characterization of KTP single crystals

Potassium titanyl phosphate (KTP) is a relatively new nonlinear optical material with excellent combination of physical properties. This paper presents the combined etching and X-ray topographic studies carried out on KTP crystals with a view to characterizing their defects. KTP crystals employed in this investigation were grown from flux. Optical microscopic study of habit faces revealed growth layers and growth hillocks on (100) and (011) faces respectively. Etching of (011) habit faces proved that growth hillocks corresponded to the emergence point of dislocation out crops on these faces. The suitability of the new etchant to reveal dislocation was confirmed by etching the matched pairs obtained by cleaving. The defects present in the crystal were also studied by X-ray topography. The defect configuration in these crystals is characteristic of crystals grown from solution. The dislocations arc predominantly linear with their origin either at the nucleation centre or inclusions. In general, grown crystals were found to have low dislocation density and often large volumes of crystals free from dislocation could be obtained.     

Defect-and-impurity state of diamond single crystals grown in the Fe–Mg–Al–C system

Special features of the formation of the defect and impurity states of diamond single crystals grown in the Fe–Mg–Al–C growth system by the temperature gradient method at the pressure 7.2–8.2 GPa and temperature 1700–1900°C have been investigated. It has been shown that as the magnesium content of the growth system increases, the type of the grown crystals changes in the following sequence: IIa → IIb.     

Unidirectional growth of <101>glycine zinc chloride single crystal by Sankaranarayanan-Ramasamy method

Single crystals of glycine zinc chloride (GZC), a semi-organic compound, were grown by conventional as well as unidirectional Sankaranarayanan-Ramasamy (SR) methods. Transparent GZC crystal of diameter 15 mm and length 50 mm was obtained by employing SR growth method. The average growth rate along <101> is 0.32 mm/day and 1.25 mm/day for crystals grown by conventional and SR methods. The crystals grown by conventional and SR methods were analyzed using chemical etching, UV-Vis and Vickers microhardness. The results show that SR method grown crystals exhibit higher transmittance and hardness possessing less dislocation density as against crystals grown by conventional method.     

Kinetics of diamond single crystal growth in Fe-Co solvents doped with titanium and zirconium

The growth kinetics of structurally perfect single crystal in the Fe-Co -C solvents with additions of Ti (1.81–5.35 at %) and Zr (0.64–6.30 at %) has been studied in the temperature range from 1380 to 1680°C at a pressure of 5.5–6.1 GPa. Concentration limits of the formation of diamond single crystals of types Ib, IIa, and an intermediate type Ib + IIb have been established. Defect-and-impurity state, habit, and special features of capturing solvent inclusions by the growing single crystals have been studied. Boundaries of the regions of variations of the habit, the degree of structure perfection, and capture of inclusions as a function of pressure and temperature have been defined in the p,T diagram of carbon.     

Hydrothermal synthesis of improved ZnO crystals for epitaxial growth of GaN thin films

ZnO single crystals with thickness up to 12 mm, 2 inches in “diameter” and weight of about 150 g have been grown from KOH, NaOH, and K₂CO₃ based hydrothermal solutions on the seeds of (0001) orientation. The addition of LiOH up to 3.0–4.5 mol/L allowed to decrease the growth rate of ZnO crystals along the 〈0001〉 crystallographic direction. For positive and negative monohedra, it was achieved 0.12 and 0.01 mm/day, respectively, at temperature 340 °С and ΔТ = 10 °С. The best ZnO etching agent was found to be the solutions 25 mol% HCl + 3 mol% NH₄F at room temperature, and etching time 5 min. The dislocation density of ZnO crystals varied from 240 cm⁻² to 3,200 cm⁻² in the case of growth rates 0.04 mm/day to 0.11 mm/day, respectively. It was also found that ZnO crystals grown are stable in air, oxygen, nitrogen, and argon atmosphere as well as in vacuum at the temperatures up to 1,000 °C under thermal treatment during 4 h.     

Etch features in Czochralski-grown single crystal indium phosphide

Two etchants for InP have been used to categorize etch features in both horizontal and vertical sections of InP single crystals grown by the Czochralski liquid encapsulation technique; these are the AB etchant, used extensively for defect analysis in GaAs and another etchant based on a phosphoric acid/hydrobromic acid mixture. The behaviour of these etchants is different but a cross correlation has been made between the types of etch feature produced. Transmission X-ray topography has been used to correlate etch features with dislocations. Nominally undoped crystals and material doped with specific impurities, e.g. Fe, Ge, Zn, have been examined. The principal features produced by etching are pits, ridges and striations. It is shown that the density and distribution of pits and ridges is consistent with these features being dislocation structures and the mechanisms by which they are revealed are discussed in terms of etching rates. The results allow comment to be made upon interface shape and the source of dislocations in InP crystals grown by the Czochralski technique.     

Etching studies on (1 0 0) faces of gel-grown ammonium dihydrogen orthophosphate crystals

Chemical etching employing specific etchants with varying etch times (20–60 s) has been successfully applied for the first time to reveal dislocation sites on the polished (1 0 0) faces of ammonium dihydrogen orthophosphate single crystals grown at ambient temperature, using a modified gel technique of double diffusion in a U-shaped beaker assembly. The selective behaviour of the etchant for straight and inclined dislocations has been demonstrated. Growth striations due to temperature fluctuations, low-angle tilt boundary and etch channels corresponding to stacking faults were clearly observed. Surface structures of the etched faces were photographed by optical and scanning electron microscopes and are discussed.     

Direct observation of Frank-Read sources in stoichiometric bismuth telluride crystals

Stoichiometric crystals of bismuth telluride have been grown from the melt by the horizontal zone levelling technique. The multiplication of dislocations and dislocation density was studied by using chemical etching. Dislocation spirals and loops due to Frank-Read sources have been observed on the basal plane.     

Growth and some properties of barium-cadmium formate single crystals: (I) Crystal growth and morphology

The growth of barium-cadmium formate BaCd(HCO₂)₄·2H₂O single crystals by slow cooling method and their characterization by selective etching are reported. It was found that BaCd(HCO₂)₄·2H₂O crystallizes from aqueous solution in 2/m class of the monoclinic system. Crystals grown during a period of 1 month have dimensions of about 2 × 1.5 × 10 cm³. The typical twinning for these crystals has been observed and investigated by the selective etching. The dislocation density has been estimated to be 3·10² – 2·10³ cm^?2.     

The growth of benzophenone crystals by Sankaranarayanan–Ramasamy (SR) method and slow evaporation solution technique (SEST): A comparative investigation

Longest unidirectional〈1 0 0〉 benzophenone (BP) crystal having dimension of 1060 mm length and 55 mm diameter was grown by Sankaranarayanan–Ramasamy method. The growth rate was measured by monitoring the elevation of the crystal–solution interface at different temperatures. The high resolution X-ray diffraction and etching measurements indicate that the unidirectional grown benzophenone crystal has good crystalline perfection and less density of defects. The optical damage threshold of SEST and SR grown BP crystals has been investigated and found that the SR grown benzophenone crystal has higher laser damage threshold value than the conventional method grown crystal. Microhardness measurement shows that crystals grown by SR method have a higher mechanical stability than the crystals grown by SEST method. Dielectric permittivity and birefringence are high in SR grown crystal compared to SEST grown BP crystal. The UV–vis-NIR results show that SR method grown crystal exhibits 7% higher transmittance as against crystals grown by conventional method.     

Special features of growing diamond single crystals in the Fe-Co-Zr-C system

The results have been considered of the investigations into the effect of various concentrations of zirconium addition to the Fe-Co alloy solvent on the growth rate and habit of a diamond single crystal grown by the temperature gradient method in the diamond thermodynamic stability region. The dependence of the defect and impurity state of grown crystals on the percentage of the zirconium addition has been established. The maximum zirconium content and temperature of the alloy solvent, which provide the growth of structurally perfect type IIa diamond single crystals, have been defined.     

Investigation on defects in HPHT-grown diamond single crystals

In the diamond single crystals synthesized at high temperature and high pressure using FeNi as catalyst, there are usually supersaturated vacancies and inclusions formed during the diamond crystal growth and rapid cooling from high temperature. Some defects such as prismatic dislocation loops, stacking faults and array of dislocations are closely related to such supersaturated vacancies and inclusions. The supersaturated vacancies agglomerate into discs on the (111) close-packed planes, subsequent collapse of the discs forms the dislocation loops and stacking faults. The thermal internal stresses, which are caused by the difference of thermal contraction between the diamond and the inclusions due to the difference of thermal coefficients between them as the diamond is cooled from high temperature, may be relieved by the formation of array of dislocations. In the present paper, these defects in the diamond single crystals were directly examined by transmission electron microscopy (TEM). The characteristics and formation process of these defects were analyzed briefly.     

Electron microscopy of layered single crystals grown by direct vapour transport method

Besides interesting properties such as optical, transport, structure, etc. possessed by crystals of transition metal dichalcogenides, they have also been found to have a potential application in the fabrication ofpec solar cells. These crystals are normally grown by carrier gas transport technique but are always contaminated by carrier gases. A new method of direct vapour transport has been developed and successfully applied to grow these crystals including those of off-stoichiometric varieties. The crystals thus grown have been characterized structurally using the techniques of x-ray powder, rotation and Weissenberg photographs and electron diffraction. Perfection studies have been made by techniques like chemical etching and electron microscopy. This review describes the electron microscopic studies made on the single crystals of the layered compounds. High resolution technique of weak beam has been employed to study dislocation pattern. Dissociated dislocations have been used to estimate stacking fault energy. Such measurements have also been carried out at different temperatures and the variation of stacking fault energy with temperature has been worked out. Interesting information regarding phase transformation for TaS₂ and W₃Se₄ in the temperature range 109 to 580 K has been derived from the electron diffraction studies and the implications have been discussed.     

Studies on bulk growth,structural and microstructural characterization of 4-aminobenzophenone single crystal grown from vertical Bridgman technique

Bulk single crystal of 4-aminobenzophenone with a size of 25 mm dia. and 35 mm length has been grown by vertical Bridgman technique. The crystal system of the grown crystal was confirmed by X-ray diffraction analysis. Crystalline perfection was analysed by high resolution X-ray diffraction studies. Chemical etching was carried out for the first time in 4-aminobenzophenone single crystal to study the defects presented in the grown crystal and the growth mechanism involved. Several organic etchants were employed with different etching time to select suitable etchant for studying dislocation pattern and other structural defects existing in the grown crystal. Etch patterns such as spirals and striations observed for the selective etchants provide considerable information on growth mechanism of the crystal.     

Dislocation density and microhardness studies in KCl-KBr mixed crystals

Crystals of KCl, KBr and different compositions of KCl-KBr mixed crystals are grown with a view to obtaining the maximum dislocation density. The density and distribution of dislocations in KCl-KBr mixed crystals have been studied as a function of composition employing the etch-pit technique. The results indicate a much greater dislocation density in the KCl and KBr crystals, compared with the mixed crystals. Microhardness measurements were carried out, using a Vicker indentation tester, for these crystals. The microhardness is found to vary non-linearly with composition. These studies show that the microhardness variation with composition is independent of the variation of dislocation density with composition.     

Investigation on structural,optical, thermal,mechanical and dielectric properties of l-proline cadmium chloride monohydrate single crystals: An efficient NLO material

In the present work, we have grown single crystals of l-proline cadmium chloride monohydrate (LPCCM) by slow evaporation solution technique (SEST) at room temperature and recorded their live growth kinetics with the help of inverted microscope. Crystal size at various stages of growth and its corresponding morphology was also recorded. Powder X-ray diffraction (PXRD) analysis of LPCCM single crystals confirmed the orthorhombic structure. Respective values of crystallite size, strain and dislocation density have been calculated using PXRD data. Metal complex coordination of the single crystal is studied by FTIR spectroscopic. The optical properties of the grown crystals were investigated through UV–VIS spectroscopic studies and shows that the crystals have very low absorption in entire characterized wavelength range 200–800 nm. The optical band gap was calculated and found to be ∼5.6 eV. Optical constants of the material is determined by theoretical calculations. The chemical etching study was also carried out to study the density of defects in the grown crystals. The photoluminous excitation and emission spectra and thermal property by TGA/DTA curve were recorded. Further, the mechanical properties have been studied using Vicker's microhardness tester as well as many parameters such as fracture toughness (K_c), Brittleness index (B_i) and yield strength (σ_ν) are presented. Dielectric studies have been carried out with varying frequency and temperatures.     

Effect of the titanium doping of the Fe—Co—C solvent on the nitrogen content of diamond single crystals grown at high pressures and temperatures

Diamond single crystals have been grown experimentally in Fe—Co-based alloys—solvents for carbon with a titanium content varying from 1 to 2 wt %. Average growth rates and morphological features of the grown crystals have been defined; the defect-and-impurity states and characteristics of macroinclusions have been analyzed. It has been found that an increase of titanium content of the Fe—Co—C solvent from 1 to 2 wt % brings about a change of the single crystal type from Ib to IIa. The use of the solvent having 1.5 wt % of titanium allows growing diamond single crystals of mixed Ib + IIb types.     

Calculation of the temperature distribution at the HPHT growing of diamond single crystals in cells with two growth layers

Finite element method was used to calculate the distribution of temperatures in growth cells of the toroid TC-40 -type HPA. The experimental investigations of the process of growing type IIa diamond single crystals were performed in high-pressure cells with two growth layers. It is shown that in using the cell materials having appropriate properties and defined configuration of the system of the resistive heating the temperature gradients are 5.4–5.6°C/mm and the growth rate is 2.46 mg/h. The total weight of obtained structurally perfect type IIa diamond single crystals in the upper and lower growth layers is 1.18 and 1.13 carats, respectively, the nitrogen content in all grown crystals is 1–3 ppt.     

Pr_(6)O_(11)对合成金刚石单晶各向异性的刻蚀EI北大核心CSCD

为了探究稀土氧化物对合成金刚石单晶的各向异性刻蚀,在氮气保护下,在750~950℃内用Pr_(6)O_(11)对合成金刚石单晶进行刻蚀。采用扫描电子显微分析、热重分析、X射线衍射和拉曼光谱等技术对刻蚀后金刚石单晶不同晶面的表面形貌、物相组成和刻蚀机理进行表征与分析。采用最大刻蚀深度、单颗粒抗压强度和冲击韧性来表征刻蚀前后金刚石性能的变化。结果表明:Pr_(6)O_(11)对金刚石{100}面和{111}面的刻蚀程度和形貌均不同;当温度为750℃时,Pr_(6)O_(11)对金刚石单晶已有一定程度的刻蚀,随刻蚀温度的增加,刻蚀加剧,且金刚石{111}面的刻蚀程度比{100}面严重;{111}面刻蚀坑形貌从三角形变为层状结构三角形,{100}面由轻微的四边形变为类蜂窝状刻蚀坑;{111}面最大刻蚀深度从1.12μm增加到12.54μm,而{100}面只从0.30μm增加到2.11μm;金刚石单颗粒的抗压强度由未刻蚀金刚石的576.25 N降低到最小530.06 N,冲击韧性由92.94 J/cm^(2)减小到88.53 J/cm^(2);Pr_(6)O_(11)对金刚石单晶的刻蚀机理在885℃前为催化石墨化,885℃后为催化石墨化和氧化。