Crystal Morphology Evolution Research Articles

Modular slot-die coater for in situ grazing-incidence x-ray scattering experiments on thin films.

Multimodal in situ experiments during slot-die coating of thin films pioneer the way to kinetic studies on thin-film formation. They establish a powerful tool to understand and optimize the formation and properties of thin-film devices, e.g., solar cells, sensors, or LED films. Thin-film research benefits from time-resolved grazing-incidence wide- and small-angle x-ray scattering (GIWAXS/GISAXS) with a sub-second resolution to reveal the evolution of crystal structure, texture, and morphology during the deposition process. Simultaneously investigating optical properties by in situ photoluminescence measurements complements in-depth kinetic studies focusing on a comprehensive understanding of the triangular interdependency of processing, structure, and function for a roll-to-roll compatible, scalable thin-film deposition process. Here, we introduce a modular slot-die coater specially designed for in situ GIWAXS/GISAXS measurements and applicable to various ink systems. With a design for quick assembly, the slot-die coater permits the reproducible and comparable fabrication of thin films in the lab and at the synchrotron using the very same hardware components, as demonstrated in this work by experiments performed at Deutsches Elektronen-Synchrotron (DESY). Simultaneous to GIWAXS/GISAXS, photoluminescence measurements probe optoelectronic properties in situ during thin-film formation. An environmental chamber allows to control the atmosphere inside the coater. Modular construction and lightweight design make the coater mobile, easy to transport, quickly extendable, and adaptable to new beamline environments.

Kinetic Monte Carlo study on the effect of growth conditions on the epitaxial growth of 3C–SiC (0001) vicinal surface

Due to the lack of research on the microscopic evolution process and the formation of step growth patterns for SiC crystals, it is of great importance to deepen the understanding of the epitaxial growth of a SiC vicinal surface from a microscopic point of view. In this study, a three-dimensional lattice kinetic Monte Carlo algorithm was used to study the step flow growth characteristics of SiC crystals. The microscopic evolution of the step flow growth patterns for SiC vicinal surfaces was shown. C and Si were treated as the basic particles, and the net deposition and diffusion of atoms were considered in this model. The periodic boundary conditions were applied along the step edge and the helical boundary conditions were applied in the direction perpendicular to the step. The surface morphology evolution of SiC crystals grown on step substrates was simulated at different growth temperatures, partial deposition fluxes, and terrace widths. The results indicated that the growth patterns of the SiC vicinal surface could be transformed from a step flow growth to a nucleation growth pattern by decreasing the growth temperature, increasing the deposition flux, and increasing the terrace width.

The effect of sulfuration reaction rates with sulphur concentration gradient dependence on the growth pattern and morphological evolution of MoS2 in laminar flow.

Sulfuration reactions dominate the synthesis of transition-metal dichalcogenides via chemical vapor deposition. A neglected critical issue is the evolution of crystal domain morphology and growth models caused by boundary layer development. In this study, we propose two growth models within a laminar flow field to investigate the kinetic mechanism of uniformly grown MoS2. We used supercritical fluid pre-deposition to obtain a well-distributed and low-crystallinity Mo precursor on the surface of a substrate to avoid non-stoichiometric supply in sulfuration. The development of the boundary layer was suppressed through mainstream force by adjusting the substrate slope angle. For growth within the underdeveloped laminar boundary layer, monolayer MoS2 with a size of 50 μm uniformly distributed on the full substrate with R = 85% (relative change in boundary layer thickness). Moreover, the growth constrained by surface chemical reactions tended to promote spatially uniform growth. However, within the fully developed laminar flow, the crystal domains preferentially grew vertically, which was attributed to the excessive crystal growth rate (g). Our results provide new insights into the controllable preparation of two-dimensional materials.

Ligand exchange induced crystal structure and morphology evolution of copper-tin-sulfur binary and ternary compounds.

In this manuscript, a simple one-pot heat-up method has been used to prepare multi-component copper-tin-sulfur nanomaterials, including binary Cu1.94S, ternary Cu4SnS4, and Cu1.94S/Cu4SnS4 nanocrystals by varying the reaction temperature, reaction time, and the type of copper source. Post-synthetic ligand exchange (LE) has further been introduced to replace the long-chain ligands originating from 1-dodecanethiol. It has been found that the LE process not only changes the surface ligands but also significantly affects the crystal structure and optical properties of nanocrystals. After LE, the crystal structures of Cu1.94S and Cu4SnS4 transformed to Cu7S4 and Cu3SnS4, respectively, with the Cu1.94S/Cu4SnS4 nanocrystals showing the same trend. This phenomenon could be ascribed to the loss of Cu+ originating from the strong complexation of Cu+ and ammonia with the formation of [Cu(NH3)n]2+ ions under aerobic conditions. Proton nuclear magnetic resonance (1H NMR) has been used to characterize the ligands on the surface before and after LE, which further demonstrated that the -SH was replaced during LE. Meanwhile, the band gaps of the obtained nanocrystals after LE show an obvious shift in the near-infrared region due to the evolution of crystal structures. This study will provide useful guidance for the LE of nanocrystals and the application of copper-based sulfide nanomaterials in optoelectronics and other fields.

Three-step growth of AlN films on sapphire substrates by metal nitride vapor phase epitaxy

Control of the growth process is important for growing high-quality AlN films. In this work, AlN films were grown on c-plane sapphire substrates by metal nitride vapor phase epitaxy (MNVPE). Interlayer was added between the buffer layer and the formal layer, and the effect of the Ⅴ/Ⅲ ratio of the interlayer on the crystal quality, surface morphology and stress evolution of the films were analyzed. An interlayer with proper Ⅴ/Ⅲ ratio can provide a stable transition from 3D growth mode to 2D growth mode, while high Ⅴ/Ⅲ ratio induce film separation. The optimum Ⅴ/Ⅲ ratio for the interlayer was found to be 11050, and the films obtained under this parameter had a FWHM of the (002) and (102) reflections were 641 arcsec and 840 arcsec, respectively. The maximum transmission is 88%. And the film separation phenomenon was found on the samples with high V/III ratio in the second step, which was thought to be the result of growing in 3D mode for a long time.

Study of the Crystallization in a Glass-Ceramic Seal

Sealing is a major issue in high temperature electrolyzers used for hydrogen production. The specifications that seals must meet are particularly demanding. In addition to sealing, the material must have mechanical, thermomechanical and chemical properties, as well as sufficient electrical resistivity. The geometries are complex and the lengths to be sealed are important. These numerous constraints lead to the use of glass powder suspended in organic solvents. This process allows for the installation of the seal by simply depositing the suspension on the areas to be sealed. A heat treatment is then applied to shape the material and ensure the sealing of the system. The use of a composition that tends to crystallize allows, a priori, improving the thermal and mechanical properties.The reference heat treatment consists of a first temperature rise followed by a crystallization stage. As the temperature rises, the organic solvents evaporate, producing CO2, which causes porosity to appear. Sintering of the glass powder also takes place during this stage. Early surface crystallization can compete with the sintering phenomenon and prevent the maximum densification of the glass ceramic by freezing the structure. The objective of the study is to obtain a seal material with maximum density, thus minimum porosity, by controlling the removal of organic solvents, sintering and crystallization.This paper will present in particular the study of the material crystallization: phases identification and evolution of crystal morphology as a function of temperature (SEM, XRD) (Figure 1), crystal surface fraction as a function of time and temperature (determined by image analysis). A poikilitic texture phenomenon, particularly important for the crystalline fraction quantification, is also detailed (SEM-EBSD). These data allow to obtain the equilibrium crystalline fraction as a function of temperature, and to further optimize the thermal treatment. Figure 1

Multi-Functionalization of Single crystals Mediated by Gel-Incorporation: A Bioinspired Strategy.

Biominerals are inherently organic-inorganic crystal composites. Drawing inspiration from this biomineral structure, functionalized single crystals can be synthesized using the gel-grown method, resulting in the incorporation of gel-networks into the host crystals. By incorporating gel-networks, diverse guest materials, such as nanoparticles and dye molecules, can be uniformly and isotropically distributed within the crystals, thereby imparting non-intrinsic optical or magnetic properties to the host crystals. Additionally, gel-incorporation enhances the toughness and stability of the crystals as the incorporated gel-fibers and accompanying guest materials act as bridges to prevent crack propagation. Furthermore, gel-incorporation enables protein crystals to exhibit self-healing properties, which can be attributed to the dynamic bonding interaction between gel-networks and crystals. Notably, recent research has demonstrated that the incorporation of zwitterionic gel-networks enhances the charge effects on crystal morphology evolution as the charged groups become bound to the developing crystal surfaces, and their detachment is impeded by the interconnected gel-networks. Therefore, preparing single crystals with gel-incorporation is a remarkable strategy for synthesizing functionalized crystal materials.

Investigation of the grain deformation to orthogonal cutting process of the textured Alloy 718 fabricated by laser powder bed fusion

In the laser powder bed fusion (LPBF), the grains grow in preferential directions depending on the scanning strategies, which results in layer-by-layer builds of particular crystallographic textures. The unique microstructure formed by LPBF results in anisotropic properties of the built structure at both macro and micro levels. To understand the grain deformation of the textured alloy fabricated by LPBF in the high-strain-rate shear process, Alloy 718 was used as an example in this work. Bulk samples with different metallurgical textures were deliberately fabricated by LPBF via three laser rotation angles, namely 0°, 67° and 90°, and then four thin slices obtained from bulks were subjected to “quasi-in-situ” grain deformation investigation through orthogonal cutting (a simple shear loading condition). The evolution of crystal orientations and morphologies, including size and shape, were traced before and after shear deformation. A full-field crystal plasticity simulation was used to quantify the stress status for grains obtained from EBSD data. This for the first time reveals the crystallographic level deformation history for hundreds of microns during a high strain rate shear removal deformation. Due to the carefully retained deformation history (i.e., typical bulges and slip bands) on the surface, a repeated deformation pattern was observed, attributing to the non-homogeneous deformation of typical build-directional blocks. The most active slip trace of deformed grain was calculated and verified based on the dominated slip bands within individual grains. The slip trace direction and intensity were quantified for different textured Alloy 718. Since the slipping-based deformation for an orientated grain is represented by its most active slip trace, a deformation tendency map is obtained by combining the shear direction, slip system and grain morphology. It reveals that grains in high texture intensity workpieces generally follow the macro shear-based deformation, while with the decrease in texture intensity, the plastic anisotropy is significant at the grain scale. Grains with similar orientations may also result in localised deformation anisotropy due to the different morphologies.

Synthesis of ZnO Crystal with Micro‐Nano Structures by a Continuous Co‐Precipitation Method: Morphological Evolution and Mechanism Analysis

AbstractZnO crystals are employed in numerous industries, but precisely controlling their morphologies is still challenging. In this work, a continuous flow process for synthesizing ZnO crystals is developed based on the co‐precipitation method. ZnO crystals at different morphologies, including needle‐like, rod‐like, flower‐like, spindle‐like, and nanospheres, are successfully prepared at low temperature. The influence of reaction temperature, pH value, ZnCl2 feeding concentration, and reaction time on the morphology, size, and purity of ZnO crystals is systematically investigated. The results of X‐ray diffraction show that the high‐purity ZnO can only be produced when the reaction temperature is above 75 °C. The band gap energies of ZnO evaluated by UV–vis diffuse reflectance spectroscopy increase with the synthesis temperature. According to scanning electron microscope (SEM) findings, the size of ZnO crystals is regulated by controlling the reaction time. Interestingly, the morphology of ZnO crystals is changed from 1D to 3D structure by controlling the feeding concentration of ZnCl2. Moreover, a concentration difference mechanism of ZnO crystal morphology evolution is proposed by monitoring the real‐time concentration of free Zn2+ ions.

Morphology Study of Hydrate Shell Crystal Growth on a Microbubble Interface in the Presence of Additives

Bubble dispersions in water can be observed in both wellbore or subsea piping as well as subsea gas seepages. The hydrate risk in subsea pipelines or methane leaks from the cold spring into seawater can be strongly influenced by the hydrate crystal growth on bubbles. In addition, the bubbling method has been proven to be an effective method to enhance the gas–liquid mixing pathway and promote hydrate’s rapid formation in the application of hydrate-based technologies, yet the microscopic mechanism of hydrate film growth on the bubbles still needs to be further clarified. In this study, the hydrate crystal growth morphology evolution at the microbubble interface was investigated by a high-resolution microscope combined with the temperature-controlled stage. The results showed that the hydrate crystals nucleated rapidly at the bubble interface to form a hydrate shell-coated structure in a pure water system. The defect growth mechanism dominated the hydrate crystals growth at the bubble interface in additive solutions. Hydrate did not nucleate directly on the surface of bubbles but by trapping guest molecules around the shrinking bubbles to form aggregated hydrate agglomeration in the presence of surfactants. In addition, the bubbles tend to provide a steady stream of gas source for hydrate formation. The growth of hydrate shells contributed to a normal distribution of bubble shrinking rates, with an average rate of 9 μm/s in 0.5 wt % NaCl solution. The existence of a high concentration of ions or organic molecules at the microbubbles’ interface and the exclusive effect played a dominant role in the process of hydrate formation. In addition, it was found that the repulsive effect of ions at the bubble interface on hydrate formation was weak under a high subcooling degree. However, other organic molecule promoters still accelerated the hydrate’s formation rate because they increased the dissolution and diffusion rate of gas in solution. The results are expected to strengthen further the applications relating to hydrate-based phase transition promotion technology in the industry in energy storage, gas separation, or inhibition techniques in flow assurance of the offshore industry.

Limits of Solid Solution and Evolution of Crystal Morphology in (La1–xREx)FeO3 Perovskites by Low Temperature Hydrothermal Crystallization

The crystallization of a new series of A-site substituted lanthanum ferrite materials (La1-xREx)FeO3 was explored by the hydrothermal method at 240 °C, for rare earth (RE) = Nd, Sm, Gd, Ho, Er, Yb, and Y, with 0 ≤ x ≤ 1. The effect of elemental substitution on the morphological, structural, and magnetic properties of the materials was studied using high-resolution powder X-ray diffraction, energy dispersive spectroscopy (EDS) on the scanning electron microscope, Raman spectroscopy, and SQUID magnetometry. If the radius of the La3+ and the substituent ions is similar, such as for Nd3+, Sm3+, and Gd3+, homogeneous solid solutions are formed, with the orthorhombic GdFeO3-type structure, and a continuous evolution of Raman spectra with composition and distinct magnetic behavior from the end members. When the radius difference between substituents and La3+ is large, such as for Ho3+, Er3+, Yb3+, and Y3+, then instead of forming solid solutions, crystallization in separate phases is found. However, low levels of element mixing are found and intergrowths of segregated regions give composite particles. In this case, the Raman spectra and magnetic behavior are characteristic of mixtures of phases, while EDS shows distinctive elemental segregation. A-site replacement induces an evolution in the crystallite shape with an increasing amount of substituent ions and this is most evident for RE = Y from cube-shaped crystals seen for LaFeO3 to multipodal crystals for (La1-xYx)FeO3, providing evidence for a phase-separation-driven evolution of morphology.

Facile Phase Control and Photocatalytic Performance of BiVO4 Crystals for Methylene Blue Degradation.

Emerging contaminants, which mainly exist as organic pollutants and pose adverse biological effects, could be removed using photocatalytic degradation, resulting in a low-cost and environmentally friendly solution. Herein, BiVO4 nanoparticles with different morphologies and photocatalytic performances were synthesized by hydrothermal treatment at different residence times. The XRD and SEM results indicate that the crystal phase of BiVO4 gradually transformed from a single tetragonal phase to a single monoclinic crystal phase as the hydrothermal time increased, and with the extension of the hydrothermal time, the morphology of BiVO4 nanoparticles gradually differentiated from a smooth spherical shape to flower-like shapes composed of polyhedrons; the size of the crystals also increased accordingly. Methylene blue (MB), used as a probe of organic pollutants, was degraded under visible light irradiation by all BiVO4 samples to investigate its photocatalytic activities. The experimental results show that the longer the hydrothermal time, the better the photocatalytic performance. The optimum hydrothermal time was 24 h, at which the sample showed the highest photocatalytic activity for MB degradation. This work shows a convenient strategy for control of the crystal phase of BiVO4-based photocatalysts based on the understanding of the crystal morphology evolution mechanism, which will benefit the researchers in designing new BiVO4-based photocatalysts with high efficiency for emerging contaminants' degradation.

Texture evolution mechanism of pulsed laser deposited in-doped Ga2O3 film affected by laser fluence and its application in solar-blind photodetector

This work explored the crystal structural, optical bandgap, and morphological texture evolution of pulsed laser deposited In-doped Ga2O3 films grown on sapphire substrate at different laser fluence from 1.0 to 2.6 J/cm2. The in situ optical emission spectroscopy was carried out to monitor the plasma radicals generated during the deposition. All the deposited films were crystallized and some clusters were formed because of high deposition temperature and rapid surface diffusion of indium (In). The growth rate and the crystallinity of the film increased and then declined with increasing laser fluence. The texture evolution mechanism of the films has been proposed firstly. The rapid diffusion of In, the sputtering and reflection effect of plasma species exist in whole films’ deposition process, which has a significant impact on the texture characteristics of the films. The clusters emerging on film surface were the crystallized In-rich InGaOx nanoparticles consisting of β-Ga2O3 and cubic In2O3 phases. Metal-semiconductor-metal solar-blind photodetectors were also fabricated and analyzed to illustrate the effect of laser fluence. The elaboration of texture evolution mechanism and effect of laser fluence on the properties of the In-doped Ga2O3 films and photodetectors is very beneficial for its application in high performance photoelectric devices.

Tailored dodecahedral polyoxometalates nanoframes with in situ encapsulated Co, N, C for oxygen evolution reaction

Hollow nanoframes with three-dimensional open architecture have diverse applications but their acquirement is still a big challenge. Herein, a crystal morphological evolution mechanism is proposed for the synthesis of dodecahedral [Co(CN)6]3-@POMs (polyoxometalates) frame-like nanostructure. Through an inside-out etching process, K3PW12O40 (POMs) dodecahedron are transformed to dodecahedral POMs nanoframes with encapsulation of [Co(CN)6]3- inside the nanochannels, which can be transformed to Co, N, C co-doped POMs nanoframes (CNCP) by a further N2-pyrolysis process. The hybrid nanoframes possess unique yolk-shell structure with multi-heteroatoms doping, showing great advantages for oxygen evolution reaction (OER). As an OER catalyst, it exhibits excellent electrochemical catalytic activities with a low overpotential of 241 mV at 10 mA cm−2, a small Tafel slope of 75.8 mV dec-1 and a long-term electrochemical stability. Our work not only provides novel dodecahedral Keggin-type polyoxometalates yolk-shell structure and nanoframes, but also provides a facile strategy to in situ encapsulate active components inside porous substrates, and thus will open a new perspective for the further utilization of POMs nanomaterials as potential catalysts for energy storage and conversion.

Revealing Size Dependent Structural Transitions in Supported Gold Nanoparticles in Hydrogen at Atmospheric Pressure.

The enhancement of the catalytic activity of gold nanoparticles with their decreasing size is often attributed to the increasing proportion of low-coordinated surface sites. This correlation is based on the paradigmatic picture of working gold nanoparticles as perfect crystal forms having complete and static outer surface layers whatever their size. This picture is incomplete as catalysts can dynamically change their structure according to the reaction conditions and as such changes can be eventually size-dependent. In this work, using aberration-corrected environmental electron microscopy, size-dependent crystal structure and morphological evolution in gold nanoparticles exposed to hydrogen at atmospheric pressure, with loss of the face-centered cubic crystal structure of gold for particle size below 4nm, are revealed for the first time. Theoretical calculations highlight the role of mobile gold atoms in the observed symmetry changes and particle reshaping in the critical size regime. An unprecedented stable surface molecular structure of hydrogenated gold decorating a highly distorted core is identified. By combining atomic scale in situ observations and modeling of nanoparticle structure under relevant reaction conditions, this work provides a fundamental understanding of the size-dependent reactivity of gold nanoparticles with a precise picture of their surface at working conditions.

Silicon drives the evolution of complex crystal morphology in calcifying algae

This article is a Commentary on Langer et al. (2021), 231: 1845–1857.

Spectral phase-field model of deformation twinning and plastic deformation

Deformation twinning is critical to understanding and predicting the heterogenous deformation of many important material systems, e.g., hexagonal metals. In this work, we report a Fast-Fourier-Transform (FFT) based spectral phase-field method (PFM) model of deformation twinning and plasticity by directly incorporating the spectral FFT elasto-viscoplastic formulation, which allows two-way coupling between morphological evolution of deformation twinning and elastoplastic deformation. We verify the model by studying the twinning morphology evolution and plastic deformation of Mg single crystals and comparing the results with existing experimental measurements. We then apply the model to investigate heterogeneous twinning nucleation, growth and propagation behaviors, including twin-twin interactions, double twinning, and twin-grain boundary interactions. This work not only provides useful insights into the underlying deformation twinning mechanisms in hexagonal crystals but also presents an efficient PFM model of deformation twinning and plasticity which is generally applicable to modelling and predicting morphological evolution of deformation twinning and its effects on elasto-plastic responses of polycrystalline materials.

Crystal phase, morphology evolution and luminescence properties of Eu3+ -doped BiPO4 phosphor prepared using the hydrothermal method.

A series of Bi1-x Eux PO4 phosphors was successfully prepared using an easy citric acid- assisted hydrothermal method. The effects of synthesis temperature, amount of citric acid, and Eu3+ concentration on the crystal phase, morphology, and luminescence properties were investigated. X-ray diffraction results revealed that BiPO4 :Eu3+ formed a hexagonal phase at 80°C, although it transformed to a monoclinic phase when the hydrothermal temperature was increased to 160°C. Moreover, it was found that a small amount of Eu3+ doping and the addition of citric acid introduced no secondary or related phases. The morphologies of the samples varied from nanoparticles to spherical microparticles to polyhedrons after the synthesis temperature was adjusted. Particle size was controlled by adding different amounts of citric acid. Under 394 nm excitation, the Bi0.95 Eu0.05 PO4 phosphor prepared at 160°C with 0.3 g of citric acid had excellent luminescence properties. A possible crystal growth mechanism during this reaction is proposed.

Shaping quality, microstructure, and mechanical properties of melt-grown mullite ceramics by directed laser deposition

Directed laser deposition (DLD) has demonstrated the potential for rapid preparing high-performance melt-grown ceramics applied for the aero-engine hot section components. Mullite has excellent potential for applications in harsh environments and extreme conditions. However, there are defects (pores and cracks) in melt-grown mullite ceramics (MGMC), limiting its application, related to unclear processes, microstructure, and properties. In this work, we investigated the impact of z-increment on shaping quality, microstructure, and mechanical properties. The results reveal that oxygen vacancy concentration is responsible for the variety of sample colors. Low z-increment is beneficial to decreasing porosity, while high z-increment is beneficial to crack suppression. The formation and propagation mechanism of internal cracks at low z-increment are discussed in detail. Mullite crystals in the sample center are "tabular cellular", which are 2:1 high-alumina mullite. While mullite crystals at the sample edge are 3:2 mullite, undergo four stages as z-increment increase; "tabular cellular", "facet dendrite", "rod cellular", and mixed crystal. This evolution of crystal morphology is attributed to the decrease in temperature gradient and the increase of supersaturation. Besides, the flexural strength and microhardness increase first and then decrease with the rise of z-increment, which is the function of defects, compactness, and microstructure.

Impact of the heat treatment conditions on crystal structure, morphology and magnetic properties evolution in BaM nanohexaferrites

Present paper reports about the strong correlation of the heat treatment conditions (annealing), crystal structure parameters, microstructure and magnetic properties evolution in nanosized BaFe12O19 M-type hexaferrites or BaM nanohexaferrites. Samples of the BaM nanohexaferrites were obtained using sol-gel method with further annealing in the range 600–1100 °C. All investigated samples were single phase and described by the P63/mmc space group. Unusual and non-linear behavior of the lattice parameters with annealing temperature increasing from 600 to 1100 °C was explained by the competition of the increase in the average crystallite size (decrease in the surface tension effect) and increase in the level of their chemical homogeneity (anionic stoichiometry). Increase of the heat treatment temperature leads to increase of the microstructure parameters (average crystal size and specific surface area) and non-linear changes in magnetic properties. Correlation of the annealing temperature and magnetic properties was discussed in terms of the structural features.