Computational analysis of three-dimensional flow and mass transfer in a non-standard configuration for growth of a KDP crystal

Computational analysis of three-dimensional flow and mass transfer in a non-standard configuration for growth of a KDP crystal was conducted. The results show that the surface shear stress is mainly affected by the inlet velocity, and the distribution of the surface supersaturation is determined by the bulk supersaturation and the inlet velocity. By adjusting the inlet velocity, the homogeneity of surface supersaturation can be improved, which is helpful for reducing the occurrence of inclusions and enhancing the crystal quality. The thickness of solute boundary layer is closely related to the flow intensity, but it is almost free from the impact of the bulk supersaturation.     

Fabrication of novel urchin-like architecture and snowflake-like pattern CuS

The interesting biomimetic morphologenesis of CuS, containing urchin-like architecture and snowflake-like pattern can be separately obtained via heating different solutions. In our case, ethanol or the mixed solvent of ethanol/H₂O containing CuCl₂ and CS₂ as raw materials in the presence of the surfactant additive cetyltrimethylammonium bromide (CTAB) have been used. The products were characterized by various techniques of XRD, SEM and ED. In the process, the solvent medium and the surfactant additive CTAB played very important roles in the formation of different biomimetic morphologies and the formation mechanisms were primarily discussed, respectively.     

Oriented growth of benzophenone crystals from undercooled melts

The tin sulfides compounds SnS and SnS₂ nanoflakes were prepared by the microwave-assisted polyol synthetic method. The as-prepared nanoscale flakes were characterized by X-ray powder diffraction, transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy and Raman spectra. The influences of solvents and microwave irradiation on the formation of products have been studied.     

Solute trapping and the effects of anti-trapping currents on phase-field models of coupled thermo-solutal solidification

We explore how the inclusion of an anti-trapping current within a phase-field model of coupled thermo-solutal growth formulated in the thin interface limit actually affects the observed levels of solute trapping during dendritic growth. The problem is made computationally tractable by the use of advanced numerical techniques including local mesh adaptivity, implicit temporal discretization and a multigrid solver. Contrary to published results for pure solutal models we find that the inclusion of such an anti-trapping current does not lead to the recovery of the equilibrium partition coefficient, except in the limit of vanishing growth velocity. At higher growth velocities non-vanishing amounts of solute trapping are observed.     

Decisive role of Au layer on the oriented growth of ZnO nanorod arrays via a simple aqueous solution method

Vertically aligned arrays of ZnO nanorod were synthesized on the Au/SiO₂/Si(1 0 0) substrate by a simple aqueous solution growth process, without pre-prepared ZnO seed layer. For comparison, glass and SiO₂/Si were also used as substrates, and the results show that the Au layer plays a decisive role in orienting the growth of the ZnO nanorod. The effects of other growth parameters, including Zn²⁺ concentration and growth time, on morphology, density, and orientation of the ZnO nanostructure were also studied and with longer reaction time, a new structure namely ZnO nanotip was obtained. Moreover, the growth mechanism of ZnO nanorod arrays grown on the Au/SiO₂/Si substrate was proposed.     

Improvement of crystal quality in ammonothermal growth of bulk GaN

Several key improvements in crystal quality of bulk GaN grown by the ammonothermal method are presented. Full width at half maximum of (0 0 2) X-ray rocking curve was reduced to 53 and 62 arcsec for Ga-side and N-side, respectively. Transparent bulk GaN crystal was also demonstrated. Oxygen and sodium concentrations were reduced to mid-10¹⁸ and mid-10¹⁵ cm⁻³, respectively. We are currently searching for a growth condition that produces transparent bulk GaN with high structural quality and low impurities. Small-sized, semi-transparent GaN wafers were fabricated by slicing the grown bulk GaN crystals, which demonstrate the high feasibility of ammonothermal growth for production of GaN wafers.     

Investigation of the growth rate of β-cyclodextrin in water during both flow-cell and batch experiments

Growth rate measurements of β-cyclodextrin in water were performed both ways. Firstly, experiments were conducted with single monocrystals located in a supersaturation-controlled flow cell. Diffusional limitations and perturbations due to a competition between surface secondary nucleation and growth at high level of supersaturation have been put in evidence. The evolution of the growth rate with supersaturation has been modelled with a BCF law, assuming a screw dislocation mechanism. Secondly seeded cooling batch trials have been carried on in a well-mixed suspension crystallizer in order to assess the growth rate of the seeds. Refractometry was used as an in situ sensor for measuring the evolution of the concentration of the solute. Measurements of the crystals size distribution of the seeds and of the final crystals are performed off line with laser diffraction technique. A kinetic law with three parameters allows a consistent assessment of the growth of the seeds. The comparison of the two sets of data shows that overall growth rate of the seed is partially limited by diffusion. Nevertheless, the estimation of a surface integration growth kinetic coefficient from batch trials is rather difficult. The theoretical framework of nucleation models developed by Mersmann et al. (Crystallization Technology Handbook, second ed., Marcel Dekker, New York, 2001, pp. 45–80 and 81–144) coupled with the estimated growth kinetics can therefore be used to better monitor the seeding process during batch crystallization operations so as to favor the growth of the seed crystals.     

Growth of CuS platelet single crystals by the high-temperature solution growth technique

Millimeter size CuS single crystals with a dark indigo blue color and a plate hexagonal shape have been successfully grown by the high-temperature solution growth technique using the KCl–LiCl eutectic as solvent. Surface microtopographic studies of the crystals indicated that the growth is made by the lateral spreading of the layers. Electrical resistivity measurements clearly show an anomaly at T55 K, related with the low-temperature structural transition, a high residual resistivity ratio of 400 and a sharp superconducting transition at T≈1.7 K confirming the very good quality of the crystals.     

Monte Carlo simulation of a cluster model for the chirality conversion of crystals with grinding

By means of Monte Carlo simulation of a cluster model, we study statistical aspect of the chirality conversion of crystals. The chirality conversion is known to occur in a saturated solution by grinding crystals, and the enantiomeric excess increases exponentially. In the simulation, with crystallization and dissolution of monomers alone, the behavior of the enantiomeric excess observed in experiment cannot be reproduced although the homochirality is realized as a result of statistical fluctuation. By allowing crystallization and dissolution of dimers, the exponential amplification of enantiomeric excess can be realized.     

Homogeneous SiGe crystals grown by using the traveling liquidus-zone method

It is indispensable to estimate a diffusion coefficient in a solution zone in order to grow a homogeneous crystal by using the traveling liquidus-zone (TLZ) method. To estimate the diffusion coefficient of Ge in the SiGe solution zone, result of a two-dimensional numerical simulation is compared with an experimental result. From the comparison, the diffusion coefficient is estimated to be 9.5×10⁻⁵ cm²/s. By using this coefficient, a sample translation rate for obtaining a homogeneous SiGe crystal is determined. By translating samples with appropriate rates, homogeneous Si_0.5Ge_0.5 crystals are successfully grown. The typical Ge composition is 0.496±0.006 for more than 13 mm long. The experimental result shows the homogeneity of ±1.2% in the mole fraction. This deviation corresponds to the variation of less than ±0.03% in the lattice constant. Since this variation is negligibly small, the homogeneity is excellent. Thus it is found that the TLZ method is the universal growth technique, which is applicable to the crystal growth of not only the III–V compounds but also the IV–IV compounds.     

Rapid synthesis of copper nanoparticles by sodium hypophosphite reduction in ethylene glycol under microwave irradiation

This paper presents a rapid method for preparation of copper metal nanoparticles by reducing CuSO₄·5H₂O with NaH₂PO₂·H₂O in ethylene glycol under microwave irradiation. The influences of the reaction parameters, such as the concentrations of reducing agent and protective polymer time of microwave irradiation, on the size and agglomeration of copper nanoparticles were investigated by X-ray powder diffraction and transmission electron microscope. Well-dispersed copper nanoparticles with diameter of about 10 nm were obtained. The use of microwave irradiation accelerated the reaction rate and benefited the dispersion and the particle size distribution of the nanoparticles.     

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.     

Sn3O4 single crystal nanobelts grown by carbothermal reduction process

This article reports on the growth of single crystal Sn₃O₄ nanobelts and SnO by a carbothermal reduction process in two different regions of a furnace tube. Even though intermediate tin oxide compounds (Sn₃O₄) have been observed experimentally, the study of structures based on them is a challenging task. Characterization data allowed us to propose that Sn₃O₄ nanobelts grew by vapor–solid mechanism while SnO grew by self-catalyst vapor–liquid–solid mechanism. Electrical measurements of a single Sn₃O₄ nanobelt were performed at different temperatures, revealing undoped semiconductor characteristics.     

Nucleation of AlN on SiC substrates by seeded sublimation growth

The nucleation of aluminum nitride (AlN) on silicon carbide (SiC) seed by sublimation growth was investigated. Silicon-face, 8 off-axis 4H-SiC (0 0 0 1) and on-axis 6H-SiC (0 0 0 1) were employed as seeds. Initial growth for 15 min and extended growth for 2 h suggested that 1850 °C was the optimum temperature of AlN crystal growth: on an 8 off-axis substrate, AlN grew laterally forming a continuous layer with regular “step” features; on the on-axis substrate, AlN grew vertically as well as laterally, generating an epilayer with hexagonal sub-grains of different sizes. The layer's c-lattice constant was larger than pure AlN, which was caused by the compression of the AlN film and impurities (Si, C) incorporation. Polarity sensitive and defect selective etchings were performed to examine the surface polarity and dislocation density. All the samples had an Al-polar surface and no N-polar inversion domains were observed. Threading dislocations were present regardless of the substrate misorientation. Basal plane dislocations (BPDs) were revealed only on the AlN films on the 8 off-axis substrates. The total dislocation density was in the order of when the film was 20– thick.     

Crystal growth rate limited by step length — the case of oxygen-deficient TiO2 exposed to oxygen

We study how an oxygen-deficient crystal of TiO₂ crystal grows when exposed to O₂. While the O flux is external to the crystal, the Ti flux necessary for growth comes from internal (bulk) interstitials (Phys. Rev. Lett. 76 (1996) 791). We address where the reaction between O and Ti to form new crystal takes place in the regime of pure step flow (i.e., surface steps advancing without new-layers nucleating). The detailed partitioning of the growth flux among individual surface steps is studied using low-energy electron microscopy for two geometries on the (110) surface—an array of islands on a terrace and an island stack generated from a dislocation source. For both geometries, the areas of islands larger than the critical size grow at rates strictly proportional to their perimeter length, independent of the local step configuration. In addition, we find that the growth rate is proportional to the O₂ pressure. The step flow represents a simple limiting case of crystal growth (Phil. Trans. R. Soc. A. 243 (1951) 299)—only the growth species near a step edge becomes incorporated into the crystal. That is, only Ti and O reactions near the step edge lead to crystal growth. This case is in marked contrast to crystal growth controlled by species attaching to terraces and diffusing to steps, for which the growth rates depend upon the local step environment. Indeed, simulating the island array as if the growth flux was partitioned among the individual islands by concentration gradients (i.e., diffusion-controlled growth) totally failed to reproduce the experimental rates.     

The inhibitory growth mechanism of saccharides on the growth of ice crystals from aqueous solutions

The inhibitory growth mechanism controlling the growth of ice crystals due to the presence of saccharides, as in plant cells, was experimentally studied at low temperature. As a result, it was found that the growth rate of ice crystals in saccharide solutions depended on the type and concentration of the saccharides. The experimental facts can be explained by the concept that giant hydrated clusters of saccharides create the framework that causes a resistance to the volume diffusion of water molecules.     

Synthesis,growth and characterization of organic nonlinear optical bis-glycine maleate (BGM) single crystals

A new organic compound of bis-glycine maleate was synthesized in the alkaline medium of 10% ammonium hydroxide solution. The bulk single crystals of Bis-Glycine Maleate (BGM) have been grown by slow cooling method. The grown crystals were characterized by employing single crystal and powder X-ray diffraction, Fourier transform infrared, optical absorption spectral studies and thermo gravimetric analysis. The microhardness studies confirmed that the BGM has a fairly high Vicker’s hardness number value (41 kg mm⁻²) in comparison to other organic NLO crystals. Second harmonic generation efficiency of the crystal measured by Kurtz–Perry powder method using Nd:YAG laser is found to be comparable to that of potassium dihydrogen phosphate (KDP). Frequency dependent dielectric studies were carried out along the major growth axis.     

Influence of some foreign metal ions on crystal growth kinetics of brushite (CaHPO4·2H2O)

Brushite, CaHPO₄·2H₂O, has been precipitated at 25 °C in the presence of Mg²⁺, Ba²⁺ or Cu²⁺ at concentrations up to 0.5 mM. When initial pH is sufficiently low to exclude nanocrystalline apatite as the initial solid phase, overall crystal growth rate may be determined from simple mass crystallization by recording pH as function of time. A combination of surface nucleation (birth-and-spread) and spiral (BCF) growth was found. Edge free energy was determined from the former contribution and was found to be a linear function of chemical potential of the additive, indicating constant adsorption over a wide range of additive concentrations. Average distances between adsorbed additive ions as calculated from slopes of plots are compatible with lattice parameters of brushite: 0.54 nm for Mg²⁺, 0.43 nm for Ba²⁺ and 0.86 nm for Cu²⁺. With the latter a sharp decrease in growth rate occurred early in the crystallization process, followed by an equally sharp increase to the previous level. When interpreted in terms of the Cabrera–Vermilyea theory of crystal growth inhibition, the results are consistent with an average distance between Cu ions of 0.88 nm, in perfect agreement with the above value.