Crystal Growth Characteristics Research Articles

Measurement and evaluation of natural frequencies of bulk ice plate using Scanning Laser Doppler Vibrometer

The structure of water in its solid state (ice) is complex. A number of process parameters and the chemistry of the freezing aqueous solution influence ice crystal growth and ice characteristics such as crystalline structure, impurity inclusions, and appearance. The resulting variation in ice properties makes determining mechanical properties challenging. This study examines the performance of a Scanning Laser Doppler Vibrometer (SLDV) used to measure the natural frequency of an ice sample and consequently evaluate its modulus of elasticity. Analytical and numerical methods were used, and the results have been compared to values found in the literature. The modulus of elasticity for the measured ice plate, with a porosity of 8.8%, was found to be 6.7 GPa, which is 2.7% lower than previously published values.

Morphological features of crystal growth in the Al87Ni8Y5 alloy on rapid cooling of the melt under high pressure

The authors have performed a comparative study of the structures of the hypereutectic Al87Ni8Y5 alloy (hereinafter indicated at.%) obtained by rapid cooling from the liquid phase during crystallization under pressure (from 1.8 to 2.2 GPa and 7 GPa), subject to temperature changes (from 1200 to 1800 °C) of the melt, through durametry, X-ray structural analysis and optical and electron microscopy. It is shown that under all the considered conditions of crystallization and the cooling rate of the melt of 103 K/sec, there are formed crystalline phases in the alloy. Dense homogeneous structures of the alloy with dispersed primary ternary aluminides Ni and Y of variable composition (with different contents of Ni and Y) or anomalously oversaturated α-Al-solid solution and modified eutectic, which have high hardness, are obtained.

Droplet re-icing characteristics on a superhydrophobic surface

Water icing is a natural phase change phenomenon which happens frequently in nature and industry and has negative effects on a variety of applications. Deicing is essential for iced surfaces, but even for a nanoengineered superhydrophobic surface, deicing may be incomplete with many adherent unmelted ice droplets which have potential for reicing. Here, we focused on the reicing characteristics of droplets on a solid superhydrophobic surface, which has lacked attention in previous studies. Our results show that the nucleation and ice crystal growth characteristics of a reicing droplet are quite different from those of a first-time icing droplet. During reicing, secondary nucleation due to fluid shear always occurs first on the edges of unmelted ice, accompanied by fast-growing ice crystals that can trigger heterogeneous nucleation when in contact with the solid surface. The reicing takes place under very small supercooling (less than 0.5 °C), and the superhydrophobic surface does not play a key role, meaning that any current icephobic surfaces lose their features, which poses great challenges for anti-icing. In addition, because of the small supercooling, no recalescence phenomenon appears during reicing and the droplet remains transparent instead of clouding. Owing to the unmelted ice floating on the top of the droplet, the droplet shape after reicing is also distinguishing from that after normal icing, but the pointy tip formation during reicing and normal icing shows a uniformity. These results shall deepen the understanding of the anti-icing and deicing physics.

Biomimetic growth, dielectric and magnetic features of copper ascorbate dihydrate crystals

Mineral ascorbates are the salts of ascorbic acid, and they are formed by bonding of mineral cation to ascorbate anion. Ascorbate salts may better tolerated by the human body than the corresponding weak acidic ascorbic acid. In this work, we depicted the methodology employed to synthesize single crystals of a new salt of ascorbic acid using copper chloride. The crystal structure was initially studied by X-ray diffraction, and further characterizations, such as spectroscopic studies (Fourier Transform Infra-Red and Micro Raman and thermal analysis (Differential Scanning Calorimetry and Thermogravimetry) were also carried out. The optical band gap of the material is determined by UV–visible spectroscopy. The polarization mechanism of the compound is explored using the dielectric measurements. Dielectric constant, a.c. conductivity and loss tangent were measured over a frequency range from 100 Hz to 5 MHz. The magnetic moment variation of magnetic field at room temperature shows a narrow magnetic hysteresis loop which indicates the weak ferromagnetic behaviour of the copper ascorbate crystal matrix.

Morphology Control by Pulsed Laser in Chemical Deposition Illustrated in ZnO Crystal Growth

The control of pulsed-laser-induced deposition was studied with the case of ZnO crystallization in a hydrothermal reaction. Crystal orientation, morphologies, and growth rate were observed to vary under different pulsed-laser irradiation conditions. Different energy barriers during nucleation and crystal growth processes were determined by stepped changes of input energy levels of a pulsed laser with the corresponding observations of the states of the material. Therefore, by precisely adjusting the pulsed-laser energy that overcomes a particular energy barrier, ZnO crystals with desired orientation and morphology could be obtained on a seedless substrate in a catalyst-free environment. Crystals varied in morphologies showed different behavior in laser-induced growth, and growth rates were orders of magnitude higher than those of other hydrothermal reactions. By analyzing crystal growth characteristics in the reaction/diffusion-limited region, a set of guidelines were defined to tune the dimensions of ZnO ...

Growth, Spectral, Linear and Nonlinear Optical Characteristics of A Novel Organic L-Proline Adipate Single Crystals

The growth and characterization of the L-Proline Adipate (LPA) nonlinear optical single crystals have been grown by slow evaporation technique at room temperature. The single crystal XRD illustrates the LPA corresponds to monoclinic system. The discrete functional groups exist in LPA were calculated by FTIR spectral investigation. The UV-VIS-NIR emits the optical properties for the grown LPA crystals. Several optical properties specifically Extinction coefficient, Reflectance, Linear refractive index were also determined. The calculated dielectric property of LPA was investigated by employing the dielectric studies. The Thermal behaviour of the LPA crystal has been found out by Thermal Gravimetric Analysis and Differential thermal Analysis. The SHG was characterized by utilizing the Kurtz Perry technique.

Halide-carbon vapor transport of ZnO and its application perspectives for doping with multivalent metals

The growth of ZnO single crystals in closed ampoules using HCl+C mixture as a chemical vapor transport agent (TA) was studied. The influence of growth temperature, TA density, C/HCl ratio, and undercooling on the ZnO mass transport rate was investigated theoretically and experimentally. The influence of growth medium composition on the features of crystal growth, such as the minimization of growth nucleus density, the increase in the lateral growth rate of up to 1 mm per day, the suppression of the attachment effect, and stable growth of non-polar, semi-polar and polar planes of a hexagonal structure was analyzed. The structural, photoluminescent, optical and electrical properties were investigated. The doping efficiency of ZnO by oxides of metals was analyzed for various TAs and Zn pressure in the growth medium. The possibility of increase in the doping efficiency by several orders of magnitude for multivalent metals was predicted for HCl+C TA.

The role of pre-annealing in the sulfurization of Cu-Zn-Sn stacked metal layer prepared by magnetron sputtering

Cu2ZnSnS4 (CZTS) films were fabricated by sulfurizing the stacked metal layer (SML) prepared by DC magnetron sputtering. The influence of pre-annealing treatment of the SML precursor on the sulfurization process and the crystal growth characteristics of the CZTS film were investigated. It was found that the crystallinity of the CZTS film was improved with the increase of the pre-annealing temperature and duration, indicating that the pre-annealing treatment promoted the sulfurization. The formation and distribution of the metal compounds in the SML dominated the sulfurization reaction. And, the microstructure and elemental composition of the CZTS film depended very much on the properties of the SML. The role of pre-annealing treatment in the sulfurization of metal stacked precursors is proposed. A highly crystalline p-type kesterite Cu2ZnSnS4 film with carrier concentration of 2.38 × 1017 cm−3, mobility of 1.38 cm2/V s and optical bandgap of 1.46 eV was obtained. The CZTS layers are expected to fabricate high efficiency thin film solar cells.

Effect of edge inclination of single crystal diamond on homoepitaxial growth

Polycrystalline diamond is easy to appear at the edge of single crystal diamond grown by homogeneous epitaxial growth, which makes it difficult to enlarge the two-dimensional surface area of single crystal diamond. In this study, the microwave plasma chemical vapor deposition (MPCVD) is used, the edge of the single crystal diamond (100) crystal face is finely cut and polished to form an inclined surface which is different from the (100) crystal plane at different angles. After being pretreatment, homogeneous epitaxial growth is carried out in a double-substrate waveguide-type MPCVD device with CH<sub>4</sub>/H<sub>2</sub> reaction gas. At the same time, the variation of plasma near the inclined plane of (100) crystal edge is analyzed by optical emission spectroscopy to study the effect of the tilting on the growth of the diamond edge. The experimental results show that the angle of the inclined surface of the edge has an effect on the quality of single crystal epitaxial growth of the edge. As the angle of the inclined surface of the single crystal diamond increases, the quantity of edge polycrystalline diamond first decreases and then increases. At an oblique angle of 3.8°, the edge exhibits complete single crystal epitaxial growth characteristics, which conduces to expand the surface area of single crystal diamond. According to the analysis, the inclined surface at different angle changes the surrounding electric field strength and plasma density of the edge, resulting in the change of carbon-containing precursors reaching the surface of the substrate. When the concentration of carbon-containing precursors on the inclined step surface is higher than the growth threshold of layered step, excessive carbon-containing precursors will constantly collide with each other and accumulate to form polycrystalline diamond on the step. When the concentration is lower than the growth threshold of layered step, the carbon-containing precursors on the surface of the substrate will be laid out to form a layered step. Therefore, the edge effect during the growth of single crystal diamond is weakened at the tilt angle of 3.8°, which leads the concentration of carbon-containing precursors on the inclined step surface to be lower than the growth threshold of layered step.

Formation of nanocrystals in an amorphous Al90Y10 alloy

Crystallization process of Al90Y10 amorphous alloy after heat treatment is investigated. Analysis of the structural transformations after heat treatment makes it possible to estimate the activation energy of crystallization and the diffusion coefficient in the deformed amorphous phase. Kissinger and Augis-Bennett models are employed to obtain the activation energy of the as-quenched alloy based on the differential scanning calorimetry (DSC) data.The crystallization of Al90Y10 amorphous alloy at high pressure torsion (HPT) is studied and the kinetic characteristics of crystal growth in a deformed matrix are determined. It is established that the nanocrystalline Al phase precipitates in the alloy subjected to HPT. The size of Al nanocrystals is measured to be about 9 nm and does not depend on deformation degree.It is suggested that the nanocrystallization of amorphous alloy during deformation is due to the simultaneous effect of structural changes in the amorphous matrix and of a local increase of the temperature during HPT processing. The local temperature increase at the crystallization front is estimated to be about 120K.

Crystal growth during keyhole mode laser welding

Evolution of microstructure during keyhole mode welding involves several special features such as multiple inflections of weld pool boundary curvatures, strong spatially variable thermal cycles and negligible undercooling. These systems are difficult to characterize rigorously, because depending on the sections selected, significantly different grain structures and topological features are observed. Here we uncover the special features of crystal growth during keyhole mode laser welding considering the motion of the melt pool and the interdependence of the grain growth in both the fusion zone and the heat affected zone. The temperature distribution and the transient thermal history of welds were combined with the grain growth simulation using a Monte Carlo approach in a computationally efficient manner. The computed results were tested against independent experimental data for keyhole mode laser welding of copper where the grain structure can be easily resolved. The results showed that the curved columnar grains growing from the fusion zone boundary coexisted with axial columnar grains near the centerline of welds. The effects of welding speed on the dimension, distribution, orientation and morphology of the columnar and equiaxed grains were studied.

Frost formation and frost meltwater drainage characteristics on aluminum surfaces with grooved structures

Frost frequently forms on refrigeration and cryogenic engineering systems. Frost on finned surfaces increases the air-side thermal resistance and reduces the airflow area, which consequently reduce the heat transfer rate. Structured fin surfaces may be an effective solution to delay frost formation and promote meltwater drainage. This study experimentally studied condensation, frost crystal growth, frost melting and meltwater drainage characteristics on aluminum surfaces with parallel and crossed grooves with comparisons to these effects on a flat aluminum surface. The results show that condensed droplets freeze later with less frost accumulation on the grooved surfaces than on the flat surface and that the frost prefers to grow at the top edges and corners of the structures instead of inside the grooves on the grooved surfaces. During melting, the frost melts and the meltwater breaks up into small meltwater streams and droplets at the top of the structures or between the structures on the grooved surfaces. The parallel grooved surface has better drainage than the flat surface with a smaller meltwater retention ratio, while the surface with crossed grooves has worse drainage. In addition, the meltwater retention ratio is related to the frost thickness. Lower surface temperatures and longer frosting time results in more frost accumulation and larger meltwater films, which are more easily shed from the surface by gravity so that the meltwater retention ratio is smaller.

Simulation of GaSb:Te Crystal Growth in Space Experiment

An application of X-ray topography methods allowed us to construct a two-dimensional map of the impurity distribution in a GaSb:Te crystal grown under microgravity conditions. This map served as a framework for the analysis of crystal growth features and of the impurity inhomogeneity in the crystal. The data on the impurity distribution in the sample became an experimental basis for the analysis of the crystallization parameters (the crystal growth rate and the maximum convection velocity) and an adequate application of theoretical models (analytical and numerical) to explaining the mechanisms of onset of impurity inhomogeneities in the crystal.

Characterization of quaternary AlInGaN films obtained by incorporating Al into InGaN film with the RF reactive magnetron sputtering technology

Al incorporation into the InGaN films has been successfully attained from the cermet targets under the working temperature of 200 °C and output power of 120 W by the RF sputtering technique. We used energy dispersive spectroscopy to analyze the compositions of the AlxInyGa1−x−yN, and X-ray diffractometry and atomic force microscopy had been taken to obtain the crystal structure and growth characteristics of the AlInGaN films. Composition-affected electrical properties of the films had been discussed by the Hall measurement, which also identified the incorporation of Al into the InGaN film in this work. A simple n-AlInGaN/p-Si diode is designed to illustrate the potential application of the sputtered AlInGaN in an electrical device.

Features of YAG crystal growth under Ar+CO reducing atmosphere

The influence of the reducing Ar+CO atmosphere on the stages of starting raw material preparation, growth and post-growth annealing of yttrium aluminum garnet, Y3Al5O12 (YAG) crystals was studied. The chemical reactions involving CO atmosphere and its impact on the raw material, melt, and crystal composition are determined. Modification of YAG optical properties under the reducing annealing is discussed.

Crystal growth and optical characteristics of beryllium-free polyphosphate, KLa(PO3)4, a possible deep-ultraviolet nonlinear optical crystal.

Deep-ultraviolet nonlinear optical crystals are of great importance as key materials in generating coherent light with wavelength below 200 nm through cascaded frequency conversion of solid-state lasers. However, the solely usable crystal in practice, KBe2BO3F2 (KBBF), is still commercially unavailable because of the high toxicity of beryllium-containing and the extreme difficulty of crystal growth. Here, we report the crystal growth and characteristics of an beryllium-free polyphosphate, KLa(PO3)4. Centimeter-sized single crystals have been easily obtained by the flux method and slow-cooling technique. The second-harmonic generation efficiency of KLa(PO3)4 powder is 0.7 times that of KH2PO4; moreover, the KLa(PO3)4 crystal is phase-matchable. Remarkably, the KLa(PO3)4 crystal exhibits an absorption edge of 162 nm, which is the shortest among phase-matchable phosphates so far. These attributes make KLa(PO3)4 a possible deep-ultraviolet nonlinear optical crystal. An analysis of the dipole moments of the polyhedra and theoretical calculations by density functional theory were made to elucidate the structure-properties relationships of KLa(PO3)4.

Quinolinium-based organic electro-optic crystals: Crystal characteristics in solvent mixtures and optical properties in the terahertz range

We investigate crystal characteristics of ionic organic π-conjugated crystals based on 4-hydroxy-3-methoxystyryl quinolinium (HMQ), which are recently developed acentric crystals showing a large nonlinear optical response and a high THz generation efficiency. Among a few of HMQ derivatives, HMQ-T crystal consisting of the HMQ cation and the 4-methylbenzenesulfonate anion, is chosen for the investigation of solubility, morphology and crystal growth characteristics including optical properties in various single solvents and solvent mixtures. Compared to the solvent mixture of non-aromatic methanol and acetonitrile, HMQ-T crystals in a solvent mixture containing an aromatic solvent (methanol/toluene mixture) exhibits a similar solubility variation with the solvent composition ratio, but based on distinguishable intermolecular interactions with solvent molecules. In addition, solvent mixtures containing an aromatic solvent show a significantly different equilibrium between benzenoid and quinoid forms of the HMQ cation. In contrast to the strong influence of solvent characteristics on solubility behavior, the investigated solvent systems only slightly influence the crystal morphology. Large HMQ-T single crystals with size up to 37 × 6 × 2 mm3 are grown by slow cooling method. We also determine the refractive index and absorption of as-grown single HMQ-T crystals in the broad THz frequency range of 0.3–10 THz.

Crystal structures and luminescence properties of NaYF4 microcrystals at different pH values

Luminescence properties of materials are closely related to their crystal structures and growth characteristics. In this study, a series of β-NaYF4:20% Yb3+, 2% Er3+ (20 and 2% represent the reactant mole percentage) microcrystals with different morphologies and sizes were synthesized using a hydrothermal route. The crystal phase, morphology, size, and upconversion luminescence properties of the as-prepared samples were characterized by x-ray diffraction, field emission scanning electron microscopy and photoluminescence analysis, respectively. The effects of the precursor solution pH value on the upconversion luminescence properties of the β-NaYF4:Yb3+, Er3+ crystals were investigated in detail. The results indicate that the preferential growth plane of the β-NaYF4 crystals was significantly influenced by the precursor pH values. Crystal plane characteristics affected the luminescence behavior of β-NaYF4 in the red and green spectral range. In addition, reasonable control of the β-NaYF4 crystal growth has a significant effect on the fluorescence lifetime.

Origin of Solubility Behavior of Polar π-Conjugated Crystals in Mixed Solvent Systems

We investigate the origins of solubility behavior of polar π-conjugated crystals in mixed solvent systems and the influence of nonpolar aromatic solvents on solubility and crystal growth characteristics. In solvent mixtures of polar nonaromatic methanol and nonpolar aromatic toluene (or o-xylene), solubility of three analogous polar crystals, consisting of a π-conjugated phenyltriene bridge between electron donor and acceptor groups, shows a maximum at the midpoint of composition. The maximal solubility mole fraction in such mixed solvent systems can be as high as 67 times as that in a single solvent. For comparison, a mixed solvent system consisting of only polar nonaromatic solvents (methanol and acetonitrile) is also examined. Main intermolecular interactions between the solute and solvent molecules in mixed solvent systems, related to the solubility behavior, are experimentally provided by the UV–vis absorption spectroscopy and 1H NMR measurements. In the presence of aromatic solvents, additional strong interactions between the solvent and π-conjugated solute molecules, such as face-to-face and edge-to-face π–π interactions including π···HO–Ar hydrogen bonds are clearly observed. The aromatic characteristics of solvents also importantly influence the morphology and polymorphism of single crystals grown by solution crystal-growth methods.

Evidence of a long C-C attractive interaction in cerussite mineral: QTAIM and ELF analyses.

Cerussite, an orthorhombic lead carbonate mineral, has a structure and physical properties that cannot be understood merely in terms of ionic anion-cation interactions. The nature of the chemical bonding in cerussite is analyzed by means of the quantum theory of atoms in molecules (QTAIM) and the analysis of the electron localization function (ELF). A long C-C attractive interaction (3.077 Å) along the c axis of the cerussite structure is evidenced by the presence of bond critical points between the C atoms of the CO(3)(2-) molecular groups. It is proposed that the Pb-O interactions, which are mostly ionic in nature, disturb the structure of the CO(3)(2-) molecular groups and promote their interaction along the c axis. The importance of this long-range interaction in the high-pressure crystal chemistry of carbonate minerals and in the explanation of some crystal growth features observed for orthorhombic carbonates is also discussed in this work.