Crystal Growth Direction Research Articles

General synthesis of 2D rare-earth oxide single crystals with tailorable facets.

Two-dimensional (2D) rare-earth oxides (REOs) are a large family of materials with various intriguing applications and precise facet control is essential for investigating new properties in the 2D limit. However, a bottleneck remains with regard to obtaining their 2D single crystals with specific facets because of the intrinsic non-layered structure and disparate thermodynamic stability of different facets. Herein, for the first time, we achieve the synthesis of a wide variety of high-quality 2D REO single crystals with tailorable facets via designing a hard-soft-acid-base couple for controlling the 2D nucleation of the predetermined facets and adjusting the growth mode and direction of crystals. Also, the facet-related magnetic properties of 2D REO single crystals were revealed. Our approach provides a foundation for further exploring other facet-dependent properties and various applications of 2D REO, as well as inspiration for the precise growth of other non-layered 2D materials.

A Dopamine Acrylamide Molecule for Promoting Collagen Biomimetic Mineralization and Regulating Crystal Growth Direction.

The reconstruction of the intra/interfibrillar mineralized collagen microstructure is extremely important in biomaterial science and regeneration medicine. However, certain problems, such as low efficiency and long period of mineralization, are apparent, and the mechanism of interfibrillar mineralization is often neglected in the present literature. Thus, we propose a novel model of biomimetic collagen mineralization that uses molecules with the dual function of cross-linking collagen and regulating collagen mineralization to construct the intrafibrillar and interfibrillar collagen mineralization of the structure of mineralized collagen hard tissues. In the present study completed in vitro, N-2-(3,4-dihydroxyphenyl) acrylamide (DAA) is used to bind and cross-link collagen molecules and further stabilize the self-assembled collagen fibers. The DAA-collagen complex provides more affinity with calcium and phosphate ions, which can reduce the calcium phosphate/collagen interfacial energy to promote hydroxyapatite (HA) nucleation and accelerate the rate of collagen fiber mineralization. Besides inducing intrafibrillar mineralization, the DAA-collagen complex mineralization template can realize interfibrillar mineralization with the c-axis of the HA crystal on the surface of collagen fibers and between fibers that are parallel to the long axis of collagen fibers. The DAA-collagen complex, as a new type of mineralization template, may provide a new collagen mineralization strategy to produce a mineralized scaffold material for tissue engineering or develop bone-like materials.

Multiscale simulations of directional ice crystal growth in sugar solutions

We present a multiscale simulation model, using a phase field model describing the directional growth of ice crystals in a sugar solution during freezing. The model is supplemented with realistic, and predictive theories on the thermodynamics and diffusion kinetics of this food system. Due to separation in length scales we solve the energy balance and mass balances on the macroscopic scale, while the growth of ice dendrites is simulated on a fine grid, moving along with the solidification front. With the multiscale model we investigate the ice crystal morphology as function of freezing rate and initial sugar concentration.

Confined Crystallization of Polymers within Nanopores

Crystallization of polymeric materials under nanoscopic confinement is highly relevant for nanotechnology applications. When a polymer is confined within rigid nanoporous anodic aluminum oxide (AAO) templates, the crystallization behavior experiences dramatic changes as the pore size is reduced, including nucleation mechanism, crystal orientation, crystallization kinetics, and polymorphic transition, etc. As an experimental prerequisite, exhaustive cleaning procedures after infiltrations of polymers in AAO pores must be performed to ensure producing an ensemble of isolated polymer-filled nanopores. Layers of residual polymers on the AAO surface percolate nanopores and lead to the so-called "fractionated crystallization", i.e., multiple crystallization peaks during cooling.Because the density of isolated nanopores in a typical AAO template exceeds the density of heterogeneities in bulk polymers, the majority of nanopores will be heterogeneity-free. This means that the nucleation will proceed by surface or homogeneous nucleation. As a consequence, a very large supercooling is necessary for crystallization, and its kinetics is reduced to a first-order process that is dominated by nucleation. Self-nucleation is a powerful method to exponentially increase nucleation density. However, when the diameter of the nanopores is lower than a critical value, confinement prevents the possibility to self-nucleate the material.Because of the anisotropic nature of AAO pores, polymer crystals inside AAO also exhibit anisotropy, which is determined by thermodynamic stability and kinetic selection rules. For low molecular weight poly(ethylene oxide) (PEO) with extended chain crystals, the orientation of polymer crystals changes from the "chain perpendicular to" to the "chain parallel to" the AAO pore axis, when the diameter of AAO decreases to the contour length of the PEO, indicating the effect of thermodynamic stability. When the thermodynamic requirement is satisfied, the orientation is determined by kinetics including crystal growth direction, nucleation, and crystal growth rate. An orientation diagram has been established for the PEO/AAO system, considering the cooling condition and pore size.The interfacial polymer layer has different physical properties as compared to the bulk. In poly(l-lactic acid), the relationship between the segmental mobility of the interfacial layer and crystallization rate is established. For the investigation of polymorphic transition of poly(butane-1), the results indicate that a 12 nm interfacial layer hinders the transition of Form II to Form I. Block and random copolymers have also been infiltrated into AAO nanopores, and their crystallization behavior is analogously affected as pore size is reduced.

Factor which governs the feature of texture developed during additive manufacturing; clarified from the study on hexagonal C40-NbSi2

C40-NbSi2 with a hexagonal unit cell is focused as a high-temperature structural material. We first attempted the fabrication of the bulk C40-NbSi2 products via selective laser melting (SLM) in additive manufacturing (AM) process. Strong crystallographic texture control wherein <0001> was parallel to the building direction, i.e. development of the so-called basal fiber texture, was achieved in this study. The texture developed in products does not largely vary by changing the scanning strategy, unlike the textures of C11b-MoSi2 with a tetragonal unit cell and a β-Ti alloy with a cubic unit cell. A comparison of these results led us to the conclusion that crystal symmetry, i.e., the multiplicity of the preferential crystal growth direction, is one of the primary factors that governs the features of the textures developed in AM-built materials.

Effects of JGB Additives on the Microstructures and Electrical Properties of Electroplated Copper Foil

Extremely thin film high quality copper foil is required to ensure high performance in electronics and slimness in secondary batteries. During the electroplating of copper foil, Janus Green B(JGB) and Collagen were introduced as additives to the electrolytes to study their effects. The structural and electrical properties of the electroplated copper foil were evaluated. When each additive was added individually, the potential was increased. Specifically, the potential of the group with 30 ppm added collagen was about 27% higher rather than the non-additive group. When Cl- ions and MPSA(3-mercapto-1-propane sulfonic acid) were added to the electrolytes without collagen and JGB, the surface roughness(Rz) increased by about 136% to 2.24 μm compared to the non-additive group. This was the highest value among all groups. However, a uniform layer with a surface roughness value below 0.3 μm was formed when less than 30 ppm and 10 ppm collagen and JGB were added, respectively, to the electrolyte. The direction of crystal growth with the JGB additives tended to go forward to the (220) direction, and the crystal size was reduced by 10~27% compared to the non-additive group. The addition of Collagen is necessary to reduce the difference in resistivity of the shiny layer and right matte layer. JGB additives were required to reduce the deviation in grain size. The results confirmed that the accelerators, inhibitors and leveler need to be properly added to form a copper plating layer with low surface roughness and to reduce differences in crystal texture of the shiny layer and right matte layer. Copper foil can be safely and uniformly deposited from electrolytes with JGB below 10 ppm and collagen below 30 ppm.

Origin of minerals in åkermanite-rich patch texture and oxygen isotopic evolution of compact Type A Ca-Al-rich inclusions from the Northwest Africa 7865 CV chondrite

We report the in-situ oxygen isotopic distributions corresponding to the petrographic-mineralogical observation on a compact Type A (CTA) Ca-Al-rich inclusion (CAI), KU-N-02, from a reduced CV3 chondrite, Northwest Africa 7865. The CTA has an igneous texture and mainly consists of spinel, melilite, and Al-Ti-rich clinopyroxene (fassaite). Oxygen isotopic compositions of the constituent minerals plot along the carbonaceous chondrite anhydrous mineral line. The spinel grains are poikilitically enclosed in the melilite and fassaite and are uniformly 16O-rich (Δ17O = approximately − 23‰). The fassaite is texturally classified into two types: blocky fassaite and intergranular fassaite. The blocky fassaite crystals exhibit growth zoning as they change from Ti-rich to Ti-poor along the inferred directions of crystal growth from core to rim, while the oxygen isotopic compositions change from 16O-poor (Δ17O = approximately − 6‰) to 16O-rich (Δ17O = approximately − 23‰) with crystal growth. The intergranular fassaite crystals exist between the melilite crystals and exhibit variable Ti abundance and oxygen isotopic compositions. Additionally, their relationships between Ti contents and oxygen isotopic composition are similar to those of the blocky fassaite. The melilite grains are homogeneously 16O-poor (Δ17O = approximately − 2‰), irrespective of their åkermanite (Åk) content. Each melilite grain generally exhibits growth zoning with increasing Åk contents from core to rim, although the melilite contains Åk-rich patches within single crystal. Åk-rich patches often include two types of fassaite: small blebby crystals attached to spinel crystals and round crystals. The oxygen isotopic compositions of the Åk-rich patch and blebby fassaite are 16O-poor (Δ17O = approximately − 2‰), similar to that of the host melilite. On the other hand, the round fassaite exhibits significant variation in oxygen isotopic compositions ranging from Δ17O = −23‰ to − 4‰, which are different from those of the host melilite. These petrographic textures and oxygen isotopic variations indicate the presence of a solid precursor with variable oxygen isotopic compositions for the CTA. The spinel and round fassaite grains are relicts of the precursor that melted in the 16O-poor nebular gas, resulting in the crystallization of the host melilite from the 16O-poor melt. The Åk-rich patches and blebby fassaite crystallized from melts trapped by the growing host melilite crystals. The blocky and intergranular fassaite crystallized after the melilite did, and the oxygen isotopic composition of the melt changed to 16O-rich during the crystallization process, suggesting that the oxygen isotopic composition of the surrounding nebular gas could be varied. The inferred oxygen isotopic evolution for CTA is consistent with those inferred for Type B CAIs, suggesting that coarse-grained igneous CAIs formed in a similar nebular environment regardless of precursor chemistry.

Novel Al1.997Hf0.003O3 High-k gate dielectric thin films grown by pulsed laser deposition using pre-synthesized target material

The present study reported pure pre-synthesized Al1.997Hf0.003O3 target for the formation of novel high-k gate dielectric thin films using pulsed laser deposition technique. High substrate temperature of 800 °C and ultra-high-vacuum condition at 10−8 Torr were used to produce stable hexagonal crystal structure of thin films with exclusive crystal growth directions in the (110) and (024) planes as evidenced by the XRD. AFM images displayed dense and uniform distribution of crystallites with RMS as low as 0.12 nm, contributing to very smooth morphology. Optical observation by the UV–Vis analysis showed that the introduction of Hf in the lattice of the Al2O3 material had significantly modified the energy bands of Al1.997Hf0.003O3, hence, improved k values. Consequently, the C–V measurements of the fabricated thin films based on Pt/Al1.997Hf0.003O3/p-Si MOS capacitor exhibited a high capacitance of ~ 202 nF at ~ 6 nm thickness and attributed to high-k value of ~ 21. The I–V measurements also revealed the electron tunnelling was reduced with thicker films of Al1.997Hf0.003O3, due to this, leakage current density was improved to ~ 10−10 A/cm2. These results revealed that Al2−xHfxO3 thin films could be significant in searching for a replacement dielectric for nanoscale MOS devices.

Recent Advances in Amino‐Based Molecules Assisted Control of Noble‐Metal Electrocatalysts

Morphology-control synthesis is an effective means to tailor surface structure of noble-metal nanocrystals, which offers a sensitive knob for tuning their electrocatalytic properties. The functional molecules are often indispensable in the morphology-control synthesis through preferential adsorption on specific crystal facets, or controlling certain crystal growth directions. In this review, the recent progress in morphology-control synthesis of noble-metal nanocrystals assisted by amino-based functional molecules for electrocatalytic applications are focused on. Although a mass of noble-metal nanocrystals with different morphologies have been reported, few review studies have been published related to amino-based molecules assisted control strategy. A full understanding for the key roles of amino-based molecules in the morphology-control synthesis is still necessary. As a result, the explicit roles and mechanisms of various types of amino-based molecules, including amino-based small molecules and amino-based polymers, in morphology-control of noble-metal nanocrystals are summarized and discussed in detail. Also presented in this progress are unique electrocatalytic properties of various shaped noble-metal nanocrystals. Particularly, the optimization of electrocatalytic selectivity induced by specific amino-based functional molecules (e.g., polyallylamine and polyethyleneimine) is highlighted. At the end, some critical prospects, and challenges in terms of amino-based molecules-controlled synthesis and electrocatalytic applications are proposed.

Deformation mechanisms in ice-templated alumina–epoxy composites for the different directions of uniaxial compressive loading

The ice-templating technique enables the fabrication of multilayered ceramic-based composite materials. Very little is known on the inelastic deformation mechanisms that evolve in this class of composite materials under compressive loading conditions and cause macroscopic failure. The current investigation is motivated by a recent study by the authors, which revealed that the uniaxial compressive response of ice-templated ceramic–polymer composites is strongly dependent on the loading direction relative to the layer orientation. The current investigation reveals that the inelastic deformation mechanisms in ice-templated alumina–epoxy composites are strongly influenced by the compressive loading orientation relative to the growth direction of ice crystals. The deformation mechanisms were investigated for the loading directions of 0° (parallel to the growth direction), 45° (to the growth direction), and 90° (to the growth direction). For 0°, kink band formation and longitudinal splitting were observed to be the primary strength limiting mechanisms. Kink band formation could be the primary strength limiting factor and responsible for the catastrophic-type compressive failure response. For the loading directions of 45° and 90°, interface delamination and fracture within the lamella walls and across the alumina–epoxy interfaces were the main deformation mechanisms. These mechanisms significantly reduced the compressive strength but attributed progressive-type failure behavior in ice-templated composites. The knowledge of the inelastic deformation mechanisms in ice-templated ceramic–polymer composites under compressive loading is vital for an improved understanding of structure–mechanical property relationships and hierarchical materials design.

Investigation of Crystal Growth in Enzymatically Induced Calcite Precipitation by Micro-Fluidic Experimental Methods and Comparison with Mathematical Modeling

Enzymatically induced calcite precipitation (EICP) is an engineering technology that allows for targeted reduction of porosity in a porous medium by precipitation of calcium carbonates. This might be employed for reducing permeability in order to seal flow paths or for soil stabilization. This study investigates the growth of calcium-carbonate crystals in a micro-fluidic EICP setup and relies on experimental results of precipitation observed over time and under flow-through conditions in a setup of four pore bodies connected by pore throats. A phase-field approach to model the growth of crystal aggregates is presented, and the corresponding simulation results are compared to the available experimental observations. We discuss the model’s capability to reproduce the direction and volume of crystal growth. The mechanisms that dominate crystal growth are complex depending on the local flow field as well as on concentrations of solutes. We have good agreement between experimental data and model results. In particular, we observe that crystal aggregates prefer to grow in upstream flow direction and toward the center of the flow channels, where the volume growth rate is also higher due to better supply.

Nanopillar composite electrodes for solar-driven water splitting

Spontaneous noble metal dopant segregation in an oxide lattice can lead to the formation of metallic clusters and extended acicular inclusions. In a thin-film process, the shape and orientation of such noble metal inclusions are governed by the crystal growth direction, giving rise to a composite material with lattice-matched metal nanopillars embedded vertically in an insulating or semiconducting oxide matrix. An interesting application of such composites is in photoelectrochemical cell electrodes, where the metallic nanopillars take on three distinct roles: forming a Schottky junction with the host matrix, providing a low-loss current path from bulk to surface, and creating an efficient electrocatalytic active site on the electrode surface. In particular, we discuss the application of vertically aligned metal–oxide nanopillar composites in photoelectrochemical water-splitting cells used for direct solar-powered hydrogen generation.

Morphology of Melt-Quenched Lead Telluride Single Crystals.

Metastable single crystals of nonstoichiometric Pb1–xTe are obtained by rapid cooling from the melt. The composition and crystallographic morphology are studied using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction. Most single crystals have cubic, pyramidal, or hemispherical shapes with sizes ranging from 50 to 400 μm. All crystals adopt the same face-centered cubic rock salt structure, and the crystal growth direction is ⟨100⟩. The bulk part of the rapidly cooled material solidifies in the form of a Te-rich polycrystalline material in which grains are separated by the PbTe–Te eutectic phase. The stabilization of nonstoichiometric Pb1–xTe provides further scope for the optimization of lead telluride-based thermoelectric materials.

Origin of manganese in nannofossil calcite based on synchrotron nanoxrf and xanes

Calcareous nannofossils are micrometric calcite platelets secreted by the photosynthetic algae named coccolithophores and incertae sedis. Calcareous nannoplankton inhabit the photic zone from coast to open-ocean and have left an abundant fossil record since the Triassic. Therefore, they constitute an interesting material for geochemical studies although they have been overlooked in comparison to foraminifera. We have analyzed manganese distribution and valence in six calcareous nannofossil species representing different ages (Recent to Jurassic) and geological settings (land sections and deep ocean core-tops) and with different structures to assess the potential of Mn as a paleobiological or paleoenvironmental proxy. Nano x-Ray Fluorescence (xrf) maps were established at the esrf id22ni and id21 beamlines and Mn k-edge x-Ray Absorption Near Edge Structure (xanes) at id21. Mn is more abundant in nannofossils from pre-Quaternary rock samples than from core-top samples. In nannofossil rock samples, Mn nanoxrf maps show distributions correlated with primary crystalline organization whereas in nannofossil core-top samples, Mn is either absent or does not follow the crystal organization. Xanes analyses show that Mn is in the form of MnCO3. All these observations argue for Mn incorporation within calcareous nannofossils controlled by diagenesis through overgrowth of secondary calcite (Ca, Mn)CO3. Crusts grew along the original crystal growth directions. The incorporation of Mn in some core-top samples highlights potential early diagenesis input when the detached platelet lies on the seafloor or is still in the water column. Mn should therefore be considered a critical tool to identify diagenetic overgrowth rather than primary environmental conditions.

Hydroxyl ions: flexible tailoring of Cu2O crystal morphology.

The precise control architectures of Cu2O crystals are very crucial, which have a significant influence on their various performances. Herein, Cu2O crystals with diverse architectures were achieved via finely adjusting the concentration of NaOH. The intriguing results showed that the addition of specific amounts of OH− to the solution was crucial to tailor the morphology and size of the resulting microcrystals. We observed the evolution of the shapes of the Cu2O microcrystals, which change from a rhombic dodecahedron to spherical, octahedral-like and then to hexapod upon the increase in the NaOH concentration. Adjusting the volume of NaOH added provides a means to vary the particle size. Furthermore, density functional theory (DFT) may reveal that OH− ions serve as an efficient coordination agent selectively adsorbing onto different crystal faces of Cu2O crystals modifying the crystal energies, inducing the structure anisotropy on crystal growth. This work reveals that an effective and facile strategy has been developed for morphology-control of Cu2O crystals.

Precursor solution-dependent secondary phase defects in CsPbBr3 single crystal grown by inverse temperature crystallization

Precursor solution-dependent secondary phase (SP) defects of CsPb2Br5 inhomogeneously distribute along CsPbBr3 crystal growth direction, which severely deteriorates the carrier transport.

Atomistic modeling of InGaN/GaN quantum dots-in-nanowire for graded surface-emitting low-threshold, blue exciton laser

While the development of the quantum photonics field, including emitter–light coupling using photonic system, has given a lot of attention, it offers quantum control of light. However, the main challenge is coupling to strongly photonic mode localization with nanosystem accuracy. This paper highlights the numerical simulations employed by atomically spin tight-binding model of realistically sized InGaN/GaN dots-in nanowire (NW) architectures. The effects of active region size/shapes, crystal growth directions, graded surface/interface properties, strain relaxation distributions, and polarization-induced potentials on the oscillator strengths of InGaN-based lasers have been investigated. The 3D nanofocused photonic modes, which have been deterministically coupled to multiple quantum dots (QDs) through graded surface/interface technique, have been demonstrated. By using a thin graded layers of a site-controlled pyramidal QDs, the photonic nanofocusing on these QDs at the nonpolar pyramid apex has been geometrically accomplished and successfully leads to stronger characteristics in terms of exciton bandgap energy and polarized emission rate compared to its polar counterpart. For optimum coupling, the nonpolar NW, with intrinsically lower built-in field, exhibits an enhancement of the QDs emission rate as high as 0.98, which is 12% greater than that in a recently reported semipolar MQD structure. The atomistic simulated emission rate for the core QDs buried in NW structure is then incorporated into a TCAD simulator to obtain laser device characteristics. Here, the achievement of truncated pyramid–electrically injected graded surface-emitting laser by nanofocusing the photonic modes formed in InGaN NW has been reported. The nonpolar laser device operates at ~ 402 nm and exhibits a threshold current of ~ 391 A/cm2, which is lower nine order of magnitude lower compared to recently reported semipolar green laser diodes. Our model benchmarking has been done against a reported experiment of polar InGaN disks in GaN NW. Significantly, this engineering innovation proves the viability of InGaN nonpolar quantum dots-in-nanowire architecture as low threshold, high polarized, coherent blue nanoscale lasing emitters, and opens future trends toward a next-generation of electrically injected and interfacial grading-emitting nanolasers operating at high-frequency up to a GHz range.

A theoretical study on the growth of low-dimensional nanocrystals on isotropic substrates

We present a theoretical model describing the growth of low-dimensional nanocrystals with various shapes on liquid surfaces. The characteristic aggregation of deposited atoms is primarily resulted from the property of isotropic and free-sustained substrates. In the subsequent growth process, the atoms diffuse along preferential growth direction after they meet and then the low-dimensional nanocrystal forms gradually. The variety of nanocrystal morphology is attributed to the deviation of seed crystal size or growth direction in the initial stage caused by inhomogeneous deposition conditions. The dependence of nanocrystal length and growth rate during the growth process was discussed, and the results are in good agreement with the experimental findings.

Humidity-Dependent Thermal Boundary Conductance Controls Heat Transport of Super-Insulating Nanofibrillar Foams

Summary Cellulose nanomaterial (CNM)-based foams and aerogels with thermal conductivities substantially below the value for air attract significant interest as super-insulating materials in energy-efficient green buildings. However, the moisture dependence of the thermal conductivity of hygroscopic CNM-based materials is poorly understood, and the importance of phonon scattering in nanofibrillar foams remains unexplored. Here, we show that the thermal conductivity perpendicular to the aligned nanofibrils in super-insulating ice-templated nanocellulose foams is lower for thinner fibrils and depends strongly on relative humidity (RH), with the lowest thermal conductivity (14 mW m−1 K−1) attained at 35% RH. Molecular simulations show that the thermal boundary conductance is reduced by the moisture-uptake-controlled increase of the fibril-fibril separation distance and increased by the replacement of air with water in the foam walls. Controlling the heat transport of hygroscopic super-insulating nanofibrillar foams by moisture uptake and release is of potential interest in packaging and building applications.

Improved magnetostriction in Galfenol alloys by aligning crystal growth direction along easy magnetization axis

Galfenol (Iron-gallium) alloys have attracted significant attention as the promising magnetostrictive materials. However, the as-cast Galfenols exhibit the magnetostriction within the range of 20–60 ppm, far below the requirements of high-resolution functional devices. Here, based on the geometric crystallographic relationship, we propose to utilize the 90°-domain switching to improve the magnetostriction of Galfenols by tuning the crystal growth direction (CGD) along the easy magnetization axis (EMA). Our first-principles calculations demonstrate that Pt doping can tune the CGD of Galfenol from [110] to [100], conforming to the EMA. Then, it is experimentally verified in the (Fe0.83Ga0.17)100−xPtx (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) alloys and the magnetostriction is greatly improved from 39 ppm (x = 0, as-cast) to 103 ppm (x = 0.8, as-cast) and 188 ppm (x = 0.8, directionally solidified), accompanying with the increasing CGD alignment along [100]. The present study provides a novel approach to design and develop high-performance magnetostrictive materials.