Crystal Growth Behavior Research Articles

Next-gen approach to the combined micro/macro-scopic measurements of crystal growth in chalcogenide thin films: The case of Se90Te10

Crystal growth in 1 µm Se90Te10 thin films deposited on a variety of substrates was studied by means of a novel combination of direct microscopic and calorimetric measurements. Differential scanning calorimetry (DSC) was used to explore the macroscopic manifestation of the crystal growth in as-deposited Se90Te10 thin films, revealing the native-like crystal growth behavior (very close to that of the bulk glass) in the films deposited on the polymeric foil. The optical microscopy determined the following sequence for the crystal growth rates ur in the thin films deposited on different substrates: urwhite glass> urSiO2 glass> >urKapton. This finding is perfectly consistent with the calorimetric data, and can be explained by the combined influences of the Na+ ions migrating from the white glass substrate to the thin film/substrate interface, and by the compressive stresses arising from the large difference between the thermal expansion coefficients of Se90Te10 and the inorganic glasses. Conformation of the calorimetric and microscopic data was validated by the description of both datasets in terms of a single set of parametrized equations based on the combination of the temperature-resolved screw-dislocation growth model and the macroscopic nucleation-growth model. The novel approach to the crystal growth research in chalcogenide thin films was introduced, demonstrating its unprecedented accuracy, robustness and overall comprehension. All major aspects of this novel approach were discussed in detail, including the necessity to consider not only the substrate properties but also the associated process of structural relaxation that may significantly alter the crystal growth near glass transition.

Growth of polycrystalline Si0.7Ge0.3 on various substrates for thermoelectric applications

Silicon germanium has been known to be one of the best thermoelectric materials for high temperature applications but has yielded mediocre efficiency values. The thermoelectric efficiency is inversely proportional to thermal conductivity, which decreases with increasing grain boundaries. To maximize the grain boundaries or decreasing grain size during crystal growth, this work aimed to observe in-situ the growth behavior of Si0.7Ge0.3 on various substrates, including SiC, Si3N4, and Si3N4:Si substrates at cooling rates of 5, 20, and 100 K/min. Sample undercooling was found to have no significant temperature dependence on SiC and Si3N4:Si with average values of 0.6 K and 1.9 K, respectively. Crystal growth behaviors were found to be dependent on the cooling rate, undercooling, and substrate materials. Higher cooling rates generated more grains and SiC was found to generate the most with the smallest portion of segregated melts, while Si3N4 was found to be the opposite. Growth behaviors were further confirmed through scanning electron microscope analyses of samples.

Exploration of crystal growth behavior in Au-based metallic glass by nanocalorimetry

The Au49Ag5.5Pd2.3Cu26.9Si16.3 (at.%) bulk metallic glass is among the promising Au-based metallic glasses with the enhanced glass-forming ability and thermal stability. However, crystal growth kinetics during the crystallization of this metallic glass remains ambiguous. In this study, the rapid crystallization of a Au49Ag5.5Pd2.3Cu26.9Si16.3 bulk metallic glass in a wide temperature range was realized by nanocalorimetry. The underlying thermodynamic and kinetic features of crystal growth were ascertained based on the Cohen and Grest (C&G), Mauro-Yue-Ellison-Gupta-Allan (MYEGA) and Schmelzer models, and the adaptability of these three models was demonstrated. The maximum crystal growth rate (0.037 m/s) and corresponding temperature (595 K) estimated by these three models were similar but different crystal growth behaviors in the deeply undercooled melt were distinguished. With an increase in undercooling, the breakdown of the Stokes-Einstein relation was discovered, and a temperature-dependent decoupling exponent was demonstrated by the Schmelzer model, causing a divergence of crystal growth rate from that estimated by C&G and MYEGA models. Moreover, screw-dislocation-mediated growth was stated as the dominant crystal growth mechanism during the crystallization of the Au49Ag5.5Pd2.3Cu26.9Si16.3 bulk metallic glass.

Growth mode control of CVD-grown WS2 monolayer flakes via O2 pre-annealing for organic surfactant oxidation

Chemical vapor deposition (CVD) using liquid solution precursors is a promising method for synthesizing uniform and large-area monolayers of transition metal dichalcogenides. Organic surfactants, such as iodixanol, are crucial additives for the uniform coating of substrates with liquid solution precursors. However, during the heating process of CVD, carbons from the incompletely decomposed organic surfactant suppress crystal growth unfavorably. Here, we investigate the role of such residual carbons in the crystal growth behavior of WS2 monolayers. The crystal growth modes were precisely manipulated by residual carbon oxidation and the precursor etching rate, which was implemented by introducing O2 pre-annealing into the CVD process. Without O2 pre-annealing, flakes of limited size and multilayers were synthesized owing to the carbonization of surfactant, whereas sufficiently oxidized residual carbons via O2 pre-annealing allow for crystal growth with a large monolayer size. Moreover, the growth modes of the flakes in terms of triangles and hexagons can be systematically controlled by the O2 amount for pre-annealing because the remnant O2 compensates for the role of H2, which manipulates the etching rate of the residual W precursors on the substrate. Our results pave the way for controlling the growth modes of CVD-grown WS2 by introducing an optimized O2 pre-annealing process.

Fast crystal growth of amorphous nimesulide: implication of surface effects.

Understanding crystallization behaviors is of utmost importance for developing robust amorphous pharmaceutical solids. Herein, the crystal growth behaviors of amorphous anti-inflammatory drug nimesulide (NIME) are systemically investigated in the glassy and supercooled liquid state as a function of temperature. A sudden over-tenfold increase is observed in the bulk crystal growth of NIME on cooling below its glass transition temperature (Tg). This fast growth behavior is known as a glass-to-crystal (GC) mode and has been reported in some molecular glasses. Fast surface crystal growth of NIME can persist up to Tg + 57°C with a weak jump in its growth rates at 30-40°C. In addition, surface crystal growth and GC growth of NIME exhibit an almost identical temperature dependence, supporting the view that GC growth is indeed a surface-facilitated process. Moreover, the bubble-induced fast crystal growth of NIME is observed in the interior of its supercooled liquid with approximately the same growth kinetics as surface crystal growth. These findings are relevant for a full understanding of the surface-related crystallization behaviors and physical stability of amorphous pharmaceutical formulations.

In situ visualization of traveling solvent growth of thin Si0.7Ge0.3 crystals

A thin compositionally uniform silicon germanium crystal was grown by the traveling solvent method (TSM). In situ observation of the melting and crystal growth behavior with different temperature profiles was carried out to study the growth mechanism for the first time. It was found that the temperature gradient and the stability of melting interface was crucial for planar growth. Otherwise, the constitutional supercooling would induce faceted, and further dendritic growth. A temperature gradient of 1 K/mm was found suitable for planar growth. Above the critical temperature gradient of 1.4 K/mm, the growth interface became faceted. The stable growth velocity was also consistent with the theory indicating that the growth was driven by diffusion. From the electron backscatter diffraction (EBSD) analysis, it was confirmed that a single crystal was successfully grown from the seed. It was clarified that the strong segregation effect and positive concentration gradient from the seed side to the feed side caused solvent trapping in the faceted tips.

Crystal Engineering of Supramolecular 1,4-Benzene Bisamides by Side-Chain Modification - Towards Tuneable Anisotropic Morphologies and Surfaces.

Benzene bisamides are promising building blocks for supramolecular nano‐objects. Their functionality depends on morphology and surface properties. However, a direct link between surface properties and molecular structure itself is missing for this material class. Here, we investigate this interplay for two series of 1,4‐benzene bisamides with symmetric and asymmetric peripheral substitution. We elucidated the crystal structures, determined the nano‐object morphologies and derived the wetting behaviour of the preferentially exposed surfaces. The crystal structures were solved by combining single‐crystal and powder X‐ray diffraction, solid‐state NMR spectroscopy and computational modelling. Bulky side groups, here t‐butyl groups, serve as a structure‐directing motif into a packing pattern, which favours the formation of thin platelets. The use of slim peripheral groups on both sides, in our case linear perfluorinated, alkyl chains, self‐assemble the benzene bisamides into a second packing pattern which leads to ribbon‐like nano‐objects. For both packing types, the preferentially exposed surfaces consist of the ends of the peripheral groups. Asymmetric substitution with bulky and slim groups leads to an ordered alternating arrangement of the groups exposed to the surface. This allows the hydrophobicity of the surfaces to be gradually altered. We thus identified two leitmotifs for molecular packings of benzene bisamides providing the missing link between the molecular structure, the anisotropic morphologies and adjustable surface properties of the supramolecular nano‐objects.

Study on the growth habit of methane hydrate at pore scale by visualization experiment

The growth habit of natural gas hydrate in formation pores directly influences its occurrence and distribution, which are fundamental factors for macroscopic reservoir properties. In order to simulate the hydrate growth at pore scale and demonstrate the growth process directly, microscopic visualization experiments were carried out using glass etching model and high-resolution video microscope in this work. The crystal growth behavior of methane hydrate was observed clearly in real time, and fluid state and system pressure were analyzed. On this basis, hydrate growth patterns and corresponding control mechanisms were investigated. The results show that for a static methane–water system, the hydrate crystal grew rapidly about 10 min after perturbation. The solution gas crystallized with water, forming colorless, transparent and polygonal crystal with sharp edge and smooth surface. The free gas crystallized with water at the gas–water interface first, resulting in a quick formation of hydrate crust. Then water passed through the hydrate crust slowly and crystallized with the free gas trapped inside hydrate crust. The resulting hydrates seemed to rough and honeycomb aggregations of tiny and tightly packed crystal particles. The two kinds of hydrate with different morphologies represent two typical hydrate growth patterns. For the hydrate growth pattern of solution gas–water, solution gas, which migrates to the crystal growth front driven by the concentration gradient, is in direct contact with water, leading to a fast crystal growth rate. For the crystal growth pattern of free gas–water, the preferentially formed hydrate crust at the gas–water interface not only separates the free gas from the water phase, but also selectively obstructs the passage of gas and only allows water to pass slowly, which slows down the hydrate growth process. This research is helpful to further understand the experimental phenomena at the core and field scale, explain the existing problems, and provide support for the research on the dissociation and exploitation of natural gas hydrate.

Multi-layered Barium and Strontium Carbonate Structures Induced by the Small Organic Dye Acid Orange 7.

The crystal growth behavior induced by small molecular additives is commonly assumed to be far less complex and rich in comparison to that obtained when using macromolecules. Herein, we demonstrate that the small organic molecule Acid Orange 7 can induce a large diversity of multi-layered barium carbonate structures. These multi-layered structures stem from the small molecule imperfectly blocking the fastest growing crystal face. By tuning the balance of growth and inhibition, we control the layer shape and thickness of the structures. Extending these strategies to strontium carbonate enables the precipitation of large quasi two-dimensional multi-layer sheets. Collectively, these findings highlight the unforeseen potential for using small organic molecules to induce the formation of complex inorganic structures.

Single Crystal Growth Behavior in High-Density Nano-Sized Aerosol Deposited Films

Solid state grain growth (SSCG) is a method of growing large single crystals from seed single crystals by abnormal grain growth in a small-grained matrix. During grain growth, pores are often trapped in the matrix and remain in single crystals. Aerosol deposition (AD) is a method of manufacturing films with almost full density from nano grains by causing high energy collision between substrates and ceramic powders. AD and SSCG are used to grow single crystals with few pores. BaTiO3 films are coated on (100) SrTiO3 seeds by AD. To generate grain growth, BaTiO3 films are heated to 1,300 oC and held for 10 h, and entire films are grown as single crystals. The condition of grain growth driving force is ΔGmax < ΔGc ≤ ΔGseed. On the other hand, the condition of grain growth driving force in BaTiO3 AD films heat-treated at 1,100 and 1,200 oC is ΔGc < ΔGmax, and single crystals are not grown.

Using cathodoluminescence to identify oscillatory zoning of perthitic K-feldspar from the equigranular Toki granite

Abstract For the first time, cathodoluminescence (CL) was used to show oscillatory zoning in perthitic K-feldspars from the equigranular Toki granite, central Japan. Based on the CL patterns, two types of zoning are identified: single core oscillatory zoning (SCOZ) and multiple core oscillatory zoning (MCOZ). The SCOZ is defined by oscillatory zoning around a single-crystal core within the K-feldspar crystal, whereas the MCOZ depicts two or more such crystal cores. The crystal cores displayed in CL images reflect the nucleation parts of magmatic K-feldspar. The existence of MCOZ patterns in K-feldspars indicates multiple nuclei. CL patterns reveal crystal growth behavior of magmatic K-feldspar in the equigranular Toki granite. CL intensities are positively correlated with titanium and barium concentrations, indicating that the CL variations depend on two factors: (1) titanium concentration as a CL activator and (2) density of Al-O−-Al structural defects. The analysis of CL images revealed that albite-rich phases in microperthite and patchperthite with low-luminescence intensities cut across the CL bands of the oscillatory zoning, indicating that the oscillatory zoning in the orthoclase-rich host phase of K-feldspar was not perturbed by the formation of microperthite and patchperthite in the post-crystallization stage. The luminescence intensities of albite-rich phases in patchperthite are lower than those in microperthite, which is due to the differences in titanium and barium concentrations between them. In the post-crystallization stage, the mass transfer of titanium and barium occurred during the formation of microperthite and patchperthite. Therefore, the difference in the luminescence intensities between microperthite and patchperthite lamellae reflects their different formation mechanisms between exsolution coarsening and dissolution-precipitation coarsening. In summary, CL analyses can be used for the evaluation of the nucleation and growth not only of anhedral K-feldspar crystals in equigranular granite but also of K-feldspar phenocrysts/megacrysts in porphyritic granite. It can reveal the spatial extent of element partitioning between the melt and crystal, along with that of mass transfer from the melt into crystals during the magma evolution. Moreover, the CL analyses can also be used for the interpretation of K-feldspar textural development during the post-crystallization stage.

Effects on the crystallite growth behavior of LaPO4 nanopowders and its mechanical properties

The effects of pH of the reaction solution and the concentration of phosphoric acid on the crystal growth behavior of LaPO4 crystallites were investigated and the mechanical properties of rare-earth phosphates were compared. As a result, the concentration of phosphoric acid of 10% was beneficial to the crystal growth of LaPO4 nanocrystalline. When the pH value of the reaction solution was 2, the size of LaPO4 crystallites increased gradually with the increasing reaction temperature, and the smallest crystallite size of 43.27 nm was obtained after heat-treatment at 1000 °C. Simultaneously, the activation energy for crystal growth of LaPO4 nanocrystalline was relatively lower (26.82 kJ mol−1). With the decreasing radii of rare-earth ions, the hardness, Young's modulus and fracture toughness of the bulk rare-earth phosphates exhibited a reduced tendency, resulted from the increase of porosity under the same preparation process.

Bubble-induced fast crystal growth of indomethacin polymorphs in a supercooled liquid

Physical stability is one of the main challenges when developing robust amorphous pharmaceutical formulations. This article reports fast crystal growth behaviors of the γ and α forms of indomethacin (IMC) initiated by bubbles in the interior of a supercooled liquid. Bubble-induced crystal growth of γ-IMC exhibits approximately the same kinetics as its surface crystal growth, supporting the view that bubble-induced crystal growth is a surface-facilitated process. In contrast, the rates of bubble-induced crystal growth of α-IMC are much faster than those of its surface crystal growth. These results indicate that the bubble-induced crystal growth not only depends on the interface created by the bubble but also strongly correlates with the true cavitation of the bubble. Moreover, bubble-induced fast crystal growth of γ- and α-IMC can be terminated at different temperatures by cooling. These outcomes are meaningful for the in-depth understanding of physical stability and pre-formulation study of amorphous pharmaceutical solids showing surface-facilitated crystal growth.

Tailoring microstructure and mechanical property of laser powder deposited Inconel 718 superalloy via hybrid processing strategies

Customized tailoring of the microstructure and mechanical properties is a longstanding and challenging requirement for the high-performance implementations of laser additive manufacturing technology in the aircraft industry. In this study, two sets of processing parameters were alternated layer by layer, forming hybrid processing strategies. Thin-wall builds of Inconel 718 superalloy were produced by laser powder deposition process to preliminarily study the effect of hybrid processing strategies on tailoring the microstructure and mechanical properties. The results indicate the hybrid processing strategies have a distinct influence on the crystal growth behavior, grain orientations and sizes, precipitations and associated tensile strengths. Under the bidirectional scanning pattern, the hybrid processing strategy could effectively tailor the macroscale orientation of coarse zigzag microstructure through adjusting and disturbing the primary-secondary dendritic arms alternate growth behavior of columnar crystals. The columnar crystal trunk size exhibits a banded feature with large value in low-velocity deposition layer and small value in high-velocity layer. Under the unidirectional scanning pattern, the hybrid processing strategy can distinctly balance the size and aspect ratio of oriented fibrous grains. The strong texture of microstructure acts as an important contributor to determine the fracture behavior and associated ultimate tensile strength. Comparing to the single processing strategies, the hybrid processing strategies show little effect on the ultimate tensile strength with a slightly increased anisotropy under bidirectional scanning pattern, while distinctly improve the ultimate tensile strength with a reduced anisotropy under unidirectional scanning pattern, showing the potential to tailor the microstructure distribution and mechanical properties with customized high-performance requirements by purposely adjusting the hybridization of processing parameters.

Effect of organic additions on crystal growth behavior of La0.8Sr0.2MnO3 nanopowders prepared via sol–gel process

The effects of the addition of AcOH and ethanol on phase composition and crystal growth behavior of La0.8Sr0.2MnO3 nanopowders prepared via sol–gel process were investigated. As a result, the phase composition of final products was not affected by the addition of ethanol or AcOH in the raw solution. The activation energy for crystal growth was firstly decreased and then increased with the continuous addition of ethanol or AcOH, while it was obviously influenced by the content of AcOH. After the addition of AcOH, the activation energy for crystal growth was reduced from 26.60 kJ/mol to 23.59 kJ/mol, and then was gradually augmented to 39.75 kJ/mol with the continuous increase. Correspondingly, the crystallite size of final products was controlled to be 48.5 nm, and the lowest activation energy for crystal growth of La0.8Sr0.2MnO3 nanopowders was obtained with water as the solvent and the AcOH/Mn molar ratio of 1:2, which was beneficial to the crystallization of La0.8Sr0.2MnO3 grains.

Synergistic Effect of Codoped Nickel Oxide Hole–Transporting Layers for Highly Efficient Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs), which feature an attractive structure for diverse applications such as tandem SCs or flexible devices, continue to be rapidly developed. Among various hole‐transporting layer (HTL) materials, nickel oxide (NiO x ) is widely used as a stable and superior HTL even though it exhibits poor conductivity. Although various methods have been proposed to overcome the low conductivity of NiO x films, codoping methods have not been extensively studied and remain poorly understood. Herein, Li:Cu:NiO x is systematically investigated to explore the synergistic effect of codoping in various NiO x HTLs and PSCs. The optical, chemical, and morphological properties of the films are characterized and the dependence of these properties on the codoping ratio are investigated. A gradual improvement of the electrical properties and a tunable Fermi energy level resulting from the Li:Cu codopants is subsequently demonstrated. Furthermore, the structure of the perovskite films on HTLs and the synergistic effect on the preferred crystal growth behavior are elucidated. An inverted PSC with high efficiency was attained as a result of the enhanced electrical properties of the NiO x HTLs and the high quality of the perovskite film, which were attributed to the synergistic effect of the Li:Cu codoping method.

Comparison of the Thermal Stress Behavior of AlN Single Crystal Growth on AlN and SiC Seeds via the Physical Vapor Transport Method through Three-Dimensional Numerical Modeling and Simulation

We extend a thermal-elastic stress model by the finite element method to evaluate anisotropic three-dimensional thermal stress in AlN bulk crystals grown on on-axis 2H-AlN and 6H-SiC seeds. The dis...

Crystal Morphology Prediction of Olanzapine Forms III and IV

AbstractIt is of great significance to explore and predict crystal growth behavior that can target the optimal growth conditions and obtain ideal properties. The ability to effectively treat schizophrenia and other psychoses has led to numerous studies of olanzapine (OZPN) polymorphs. There are four reported anhydrous forms of OZPN, but two of whose crystal morphologies (forms III and IV) are still unavailable in the laboratory. Based on the advanced spiral growth model, this study predicts the crystal morphologies of OZPN forms III and IV from vapor and different solvents (i.e., water, ethyl acetate, ethanol, cyclohexane, and dichloromethane), where the potential energies between dimeric growth units (stronger than specific energy cutoff) are considered as strong bond. It is demonstrated that the growth rate of form III increases with the increase of supersaturation from 1.01 to 1.07. Form III crystallizes from solvents with the block‐like shape, whereas form IV grows with the rectangular shape, that obviously differs from the flat‐square shapes of form I and form II. This mechanistic model is able to apply on various compounds, especially for the crystals with non‐centrosymmetric molecules to obtain important guidance for their experimental preparations.

Understanding of crystallization behaviors in laser 3D printing of bulk metallic glasses

In 3D printing of bulk metallic glasses (BMGs) by selective laser melting (SLM), partial crystallization normally occurs in heat-affected zones (HAZs), which significantly deteriorates the properties of 3D-printed BMGs. To understand which factor dominates amorphous-to-crystalline conversion of 3D-printed BMGs, two representative BMG alloys with different glass forming ability (GFA), i.e., Zr55Cu30Ni5Al10 (named as Zr55 with high GFA) and Zr60.14Cu22.31Fe4.85Al9.7Ag3 (named as ZrAg with low GFA), were selected for SLM 3D printing, and their crystallization behaviors were comparatively studied. It is revealed that the 3D-printed ZrAg BMG with low GFA always possessed a higher amorphous phase content than the Zr55 BMG with a high GFA under different laser energy inputs. Thermal analysis and TEM observations revealed that crystal growth rate is the crucial factor for the resistance against amorphous-to-crystalline conversion in 3D-printed BMGs, as the ZrAg system exhibited much lower crystal growth rate although it has a lower GFA. The different crystal growth behavior of the two BMGs is associated with their different crystallization mechanisms: ZrAg BMG follows the mode of primary-type crystallization with multiple phases formation, leading to a low crystal growth rate, while Zr55 BMG follows the mode of polymorphous-type crystallization, which is characterized with formation of a simple crystalline phase, thus leading to a high crystal growth rate. The present work sheds light on the understanding of crystallization mechanism in 3D-printed BMGs and provides a guide for selection or design of BMG compositions for 3D printing.

Investigation of thermoelectric properties in binary Sb-Te and Sn-Te alloys during crystallization process

The nanometric phase-separation and crystal-growth behaviors occur continuously in Sb7Te3 alloy during phase-change process. It is strongly suggested that the phase separation hinders the improvement of Seebeck coefficient and power factor. Nevertheless, a dual-phase nanoprecipitate-embedded Sn7Te3 films with an improved thermoelectric performance is reported compared with Sb7Te3 films. Sn7Te3 alloy can significantly improve the thermopower factor from ~23.2 to ~ 1841.8 µW/mK2, which is attributed to the coexistence of dual-phase SnTe+Sn nanoprecipitates. This can effectively enhance the carrier transport and thus significantly enhance power factor. In this study, the basic phase separation mechanism in Sb7Te3 matrix is clarified, and the dual-phase engineering in Sn7Te3 is proved to be an effective way to improve the thermoelectric performance, which provides a new way to realize the high-performance properties of thermoelectric films.