Crystallographic Faces Research Articles

A Facile Microwave-Promoted Formation of Highly Photoresponsive Au-Decorated TiO2 Nanorods for the Enhanced Photo-Degradation of Methylene Blue.

The integration of noble metal nanoparticles (NPs) effectively modifies the electronic properties of semiconductor photocatalysts, leading to improved charge separation and enhanced photocatalytic performance. TiO2 nanorods decorated with Au NPs were successfully synthesized using a cost-effective, rapid microwave-assisted method in H2O2 and HF media for methylene blue (MB) degradation under visible light illumination. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 physisorption, and UV-vis spectroscopy were employed to characterize the structures, morphologies, compositions, and photoelectronic properties of the as-synthesized materials. The fusing of Au NPs effectively alters the electronic structure of TiO2, enhancing the charge separation efficiency and improved electrical conductivity. The HF treatment promotes the exposure of the highly reactive (001) and (101) crystalline facets. The improved photocatalytic activity of Au/TiO2, achieving 97% efficiency, is attributed to the surface plasmon resonance (SPR) effect of the Au NPs and the presence of oxygen vacancies. The photodegradation of MB using the TiO2/Au photocatalysts follows pseudo-first-order kinetics, highlighting the enhanced catalytic efficiency of the synthesized nanostructures. The exceptional properties of the binary Au/TiO2 photocatalysts, including the SPR effect, exposed crystallographic faces, and efficient charge carrier separation through a decrease in the recombination of electrons and holes, contribute to the photocatalytic degradation of MB.

Real-Time Observation for MoS2 Growth Kinetics and Mechanism Promoted by the Na Droplet.

While the molten salt-catalyzed chemical vapor deposition (CVD) technique is recognized for its effectiveness in producing large-area transition metal chalcogenides, understanding their growth mechanisms involving alkali metals remains a challenge. Here, we investigate the kinetics and mechanism of sodium-catalyzed molybdenum disulfide (MoS2) growth and etching through image analysis conducted using an integrated CVD microscope. Sodium droplets, agglomerated via the thermal decomposition of the sodium cholate dispersant, catalyze the precipitation of supersaturated MoS2 laminates and induce growth despite fragmentation during this process. Triangular MoS2 crystals display a distinct self-exhausting exponential behavior and slow growth of thermodynamically favorable crystallographic faces, exhibiting a sulfur-dominant pressure. The growth and etching processes are facilitated by the scooting of sodium droplets along grain edges, displaying comparable rates. Leveraging these kinetics makes it possible to engineer atypical MoS2 shapes. This combined microscope not only enhances the understanding of growth mechanisms but also contributes to the facile development of next-generation nanomaterials.

Особенности термореакционной способности электролитических никелевых покрытий с различной морфологией поверхности

Nickel coatings consisting of oriented structures have unique catalytic properties. However, the temperature range for the use of such coatings is not determined, and a comprehensive study of their thermal properties in aggressive environments is required. This work studied the influence of the characteristics of the habit of nickel crystals on their reactivity with increasing temperature (thermoreactivity). The authors studied nickel coatings produced by electrodeposition with the addition of inhibitory additives, in the form of alkali metal chlorides to the electrolyte. Differential thermal analysis was used to study the reactivity of coatings in temperature fields. Oxygen was used as an aggressive medium. The phase composition of the samples after heating was determined, using a powder X-ray diffractometer. The introduced additives in the form of alkali metal chlorides allowed forming coatings consisting of crystals of a cone-shaped habit. It was found that the introduction of additives, in the form of alkali metal salts into the electrolyte, makes it possible to change the habit of nickel crystals, and increase the surface area of the coating by approximately 10–15 %. The study showed that electrodeposited nickel coatings, consisting of crystals in the form of micro- and nanocones, have (compared to the control coating) a reduced thermoreactivity. Experimental data allowed concluding that a decrease in the intensity of oxidation on the coatings under study, may be associated with the presence of a preferential development of certain crystallographic faces of the crystals, which causes a change in the nature of the nickel-oxygen interaction, and as a consequence, a change in the oxidation intensity.

The effect of build orientation on tensile properties and corrosion resistance of 316L stainless steel fabricated by laser powder bed fusion

The effects of build orientation on tensile property and corrosion behavior of laser powder bed fusion 316L stainless steel were investigated. The laser powder bed fusion 316L stainless steel in normal direction exhibited lower tensile strength and elongation than one in build direction. In view of the fact that there was no obvious martensitic transformation in the two samples, high density dislocation and more low-angle grain boundaries in laser powder bed fusion 316L stainless steel in build direction both enhanced tensile yield and tensile strength. More deformed twins in the sample in build direction induced better plasticity. In addition, laser powder bed fusion 316L stainless steel in build direction exhibited better corrosion resistance than one in normal direction in borate buffer and sodium chloride solutions. This was attributed to the larger grain and more densely packed crystallographic faces in build direction for laser powder bed fusion 316L stainless steel.

Self-Patterning Tetrathiafulvalene Crystalline Films.

Tetrathiafulvalene (TTF) crystals grown from the melt are organized as spherulites in which helicoidal fibrils growing radially from the nucleation center twist in concert with one another. Alternating bright and dark concentric bands are apparent when films are viewed between crossed polarizers, indicating an alternating pattern of crystallographic faces exposed at the film surface. Band-dependent reorganization of the TTF crystals was observed during exposure to methanol vapor. Crystalline growth appears on bright bands at the expense of the dark bands. After a 24 h period of exposure to methanol vapor, the original spherulites were completely restructured, and the films comprise isolated, concentric circles of crystallites whose orientations are determined by the initial TTF crystal fibril orientation. While the surface of these outgrowths appears faceted and smooth, cross-sectional SEM images revealed a semiporous inner structure, suggesting solvent-vapor-induced recrystallization. Collectively, these results show that crystal twisting can be used to rhythmically redistribute material. Crystal twisting is a common and often controllable phenomenon independent of molecular or crystal structure and therefore offers a generalizable path to spontaneous pattern formation in a wide range of materials.

Effects of Size and Shape on the Tolerances for Misalignment and Probabilities for Successful Oriented Attachment of Nanoparticles

Oriented attachment (OA) of nanoparticles is an important pathway of crystal growth, but there is a lack of tools to model OA. Here, we present several simple models that relate the probability of achieving OA to basic geometric parameters, such as particle size, shape, and lattice periodicity. A Moiré-domain model is applied to understand twist misorientations between parallel surfaces, and it predicts that the range of twist angles yielding perfect OA is inversely related to the width of the contact area. This idea is explored further through a surface functional model, which investigates how patterns of crystallographic registration can drive the emergence of complex orientational energy landscapes. The energy landscapes are predicted to possess multiple local minima that can trap particles in imperfect alignments, and these local minima become deeper and more numerous as the contact area increases, which makes OA more challenging for large particles. A second set of models is presented to understand the sequence of events by which two crystallographic faces become coplanar after the collision. We use a central force approximation to predict the odds that two particle faces will attain coalignment when the particles collide with random misalignments, and we show that in the absence of special biasing forces, the probability of attaining alignment on a given face is roughly proportional to its solid angle as viewed from the center of the particle. The model thus predicts that OA is most favorable between well-faceted particles and becomes exceedingly unlikely for large spherical particles that express many microfacets.

Effect of Polar Faces of SiC on the Epitaxial Growth of Graphene: Growth Mechanism and Its Implications for Structural and Electrical Properties

In this study, epitaxial graphene layers of cm2 sizes were grown on silicon carbide (SiC) substrates by high-temperature sublimation. The behavior of the two crystallographic SiC-polar faces and its effect on the growth mechanism of graphene layers and their properties were investigated. Crystallographic structural differences observed in AFM studies were shown to cause disparities in the electrical conductivity of the grown layers. On the silicon-polar (Si-polar) face of SiC, the graphene formation occurred in spike-like structures that originated orthogonally from atomic steps of the substrate and grew outwards in the form of 2D nucleation with a fairly good surface coverage over time. On the carbon-polar (C-polar) face, a hexagonal structure already formed at the beginning of the growth process. On both polar faces, the known process of step-bunching promoted the formation of nm-scale structural obstacles. Such a step-bunching effect was found to be more pronounced on the C-polar face. These 2D-obstacles account for a low probability of a complete nano-sheet formation, but favor 2D-structures, comparable to graphene nanoribbons. The resulting direction-dependent anisotropic behavior in electrical conductivity measured by four-point probe method mainly depends on the height and spacing between these structural-obstacles. The anisotropy becomes less prudent as and when more graphene layers are synthesized.

Crystallographic parameters of spherulitic structures in ferroelectric film

The symmetry and structure of ferroelectric films determine most of their properties. Nonlinear optical technique of second harmonic generation (SHG) is widely accepted for remote and fast qualitative characterization of ferroelectric films. In this article, we develop a method for quantitative characterization of the local symmetry and structure of PZT thin films. Depending on the annealing time of pyrochlore phase two types of structure have been obtained: continuous perovskite polycrystalline film consisting of truncated spherulites and isolated spherulites embedded into pyrochlore matrix. The method is based on the SHG azimuthal dependences measurements followed by fitting procedure and gives the ratio of monoclinic to tetragonal phases as well as the fraction of differently oriented crystallographic faces of both of these phases.

NH4Cl and KCl effect on the structural, morphological, optical and electrochemical properties of Cu2O nanoparticles and Cu2O nanostructures, galvanostatically electrodeposited

In this work, Cu2O polyhedrons with two different shapes were synthesized, using the galvanostatic electrochemical deposited method. In copper nitrate (Cu(NO3)2) and Potassium chloride (KCl) bath, the Cu2O show highly symmetric 26-facet polyhedral microcrystals with well-defined {100}, {110}, {111} crystallographic faces. While, in the presence of additive (NH4Cl), Cu2O shows 18-polyhedral with well-developed {100} and {110} faces. The two morphologies revealed p-type semiconducting behavior. Cu2O 26-facet polyhedral show a high photoelectrochemical (PEC) stability of 73.5%. Such a feature is of great importance for future water splitting applications. Furthermore, the influence of the potassium chloride (KCl) upon their structural, morphological, conduction type, and optical properties, were investigated, studying the Cu2O nanostructures electrodeposited. Cu2O thin films were prepared from copper sulfate as a precursor (CuSO4), using different concentrations of potassium chloride (KCl). Structural, optical, and morphological properties of films, which were obtained by galvanostatic mode, were observed using X-ray diffraction, UV–visible spectrophotometer, and scanning electron microscopy, in addition to Mott-shotcky measurement, for an electrochemical characterization, and photocurrent measurement. . It was shown that the conduction type of Cu2O nanostructures does not change regardless of the KCl concentration in the electrolyte. However, chlorine ions can ameliorate the density of the donor carriers (30 times largest) and the morphologie can be totally changed when the concentration of Cl− ions attends 0.1 ​M from nanocubes to dendrites of polyhedral shape.

Combined in vitro and in vivo investigation of barite microcrystals in Spirogyra (Zygnematophyceae, Charophyta)

We have investigated the biomineralisation of barite ‒a useful proxy for reconstructing paleoproductivity‒ in a freshwater alga, Spirogyra, by combining in vitro and in vivo approaches to unveil the nature of its barite microcrystals. Scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDXS) observations on simply dried samples revealed that the number and size of barite crystals were related to the barium concentration in the media. Additionally, their morphology showed a crystallographic face (011), which is not normally observed, suggesting the influence of organic molecules on the growth kinetics. The critical point drying method was used to preserve the internal and external structures of Spirogyra cells for SEM imaging. Crystals were found adjacent to the cytoplasmic membrane, near chloroplasts and fibrillary network. In vivo optical microscopy and Raman tweezer microspectroscopy in living cells showed that barite microcrystals are optically visible and follow cytoplasmic streaming. These results led us to propose that barite formation in Spirogyra occurs in the cytoplasm where barium and sulphate are both available: barium supplied non-selectively through the active transport of the divalent cations needed for actin polymerisation, and sulphate because necessary for amino acid biosynthesis in chloroplasts.

Oxide-Ion Diffusivity in Fluorite and Perovskite Oxides for Inert Anode in Molten Salts and their Characterization

This study characterizes the oxide-ion diffusivities of fluorite and perovskite oxides for an inert anode in molten salts below intermediate temperatures (∼800 K) and investigates the morphologies of nanoparticles used for nanostructure-fabricating the inert anode to optimize the oxide-ion diffusivity using phonon vibration. The isotropic phonon vibration of each material was estimated using high-temperature X-ray diffraction measurements. Both fluorites and perovskites exhibited a tendency for high oxide-ion diffusivity, as confirmed at a high-vibrational, oxide-ion frequency. Crystal anisotropy measurements of phonon vibration indicated that the oxide ions diffuse isotropically and three-dimensionally in each crystallographic face of fluorites while they diffuse preferentially along the (a, b) plane in perovskites. These results suggest that the oxide-ion diffusivity was improved using spherical fluorite nanoparticles and curtailed using layered perovskite particles.

Molecular insights into the heterogeneous crystal growth of tetrahydrofuran hydrate: Kinetic and interfacial properties

The present work aimed to explore molecular insight into the tetrahydrofuran (THF) hydrate growth along its crystallographic face to consider the heterogeneous conditions. Molecular dynamic (MD) simulation results provided detailed dynamical aspects of water, and THF molecules at the interface of aqueous solution/hydrate slab by using the F3 order parameter, and visual snapshots of the system at different times. Our simulations revealed that the interfacial properties of the hydrate phase can change the local structure of water molecules in the liquid phase and thus alter the kinetics of hydrate formation. Furthermore, the behavior of THF solution on the copper surface under the hydrate-forming conditions has been studied. It was found that the copper surface affected the THF solution by changing the distribution of THF and water molecules near the liquid-solid interface. Also, the MD simulation showed that a layer of THF molecules was adsorbed on the copper surface and subsequently, a dense water film was formed resulting in a strong resistance to order the water molecules around the THF for hydrate formation. These results are illustrative of how interfacial properties can affect the heterogeneous crystal growth of the hydrate phase.

Newly Synthesized Micro-Nano Transition Metal Complexes of Hexadecanoic Acid as Anti-Microbial Agents: Synthesis, Characterization, and Biological Investigations

The synthesis of several metal complexes of d-block elements of hexadecanoic acid (palmitic acid) and its antimicrobial activity was reported in this study. UV-Vis and FT-IR spectroscopy studies were used to characterize and confirm the produced metal complexes by the shift in the absorbance and the formation of M-O linkage. The X-ray diffraction method was mainly used to examine the crystallographic faces of the complexes based on the transition metals. Thermal gravimetric investigation revealed that all metal palmitate complexes had high thermal stability in the range of 250-300°C. The metal complexes of hexadecanoic acid were examined for microbicidal activity against diverse bacterial strains and fungal pathogens using the agar well diffusion method. The copper palmitate complex presented excellent antibacterial activity among the other metal complexes. These outcomes suggest of using fatty acid metal complexes as a suitable candidate in several biomedical applications.

Pressure and Temperature Induced Dual Responsive Molecular Crystals: Effect of Polymorphism

The rapid conversion of energy into mechanical motion is a crucial requirement in the design of advanced flexible sensors and optoelectronic devices. Responsive materials that show mechanical movement when exposed to different external stimuli such as heat, pressure, humidity, or light can serve as technomimetics in smart actuator and microrobotic devices. However, it is quite challenging to design molecular crystals which can respond to two or more external stimuli. Herein, we report dimorphic forms (1a and 1b) of 2-hydroxy-3,5-dibromobenzylidine-4-fluoro-3-nitroaniline (Crystal 1) where form 1a is brittle and form 1b is elastically bendable. Both polymorphs exhibit progressive thermosalient responses which are seemingly different in nature. One polymorph (1a) shows jumping, while the other (1b) shows bending. The property difference is solely attributed to the inherent crystal packing and linked to the differences in the molecular conformations, structural packing, and intermolecular interactions. 2-Hydroxy-3-bromo-5-chlorobenzylidine-4-fluoro-3-nitroaniline (Crystal 2) was nonthermosalient but was mechanically flexible. Variable temperature powder X-ray diffractometry revealed anisotropic crystallographic face expansion─a possible explanation for the different thermosalient behaviors of the dimorphs.

Identifying crystallographic faces of the fluorites urania and thoria with rotational polarized Raman spectroscopy

AbstractCrystallite orientation identification is invaluable, but is often limited to small area identification or requires a large area sample. Nondestructive optical methods such as polarized Raman spectroscopy, in contrast, can be used to completely map a variety of sample sizes, but their potential is not yet fully realized. Here, we report a systematic study of polarized Raman scattering of high‐quality, hydrothermally grown, single crystals of urania and thoria. The peak intensity variations for as‐grown major crystal planes, post‐growth polished crystal planes, and a post‐growth polished non‐crystallographic plane are directly linked to crystallographic orientation and crystal rotation, and agree with computed models. In particular, the parallel polarized peak intensity results are directly correlated with metal–oxygen–metal chains in the fluorite structure and can be used to determine both orientation and rotational alignment of a given crystal face if sufficiently small rotational steps are applied. These results are structure based, being applicable to the larger fluorite phase space, which is useful for optical, semiconductor, nuclear, and solid oxide fuel cell industries. Further, these results suggest that Raman spectroscopy can identify non‐crystallographic orientations that are not discernable by traditional means.

Imparting Superhydrophobicity to Porphyrinic Coordination Frameworks Using Organotin

Imparting Superhydrophobicity to Porphyrinic Coordination Frameworks Using Organotin

Surface Chemistry, Crystal Structure, Size and Topography Role in the Albumin Adsorption Process on TiO2 Anatase Crystallographic Faces and Its 3D-Nanocrystal: A Molecular Dynamics Study

TiO2 is widely used in biomaterial implants. The topography, chemical and structural properties of titania surfaces are an important aspect to study. The size of TiO2 nanoparticles synthetized by sol–gel method can influence the responses in the biological environment, and by using appropriate heat treatments different contents of different polymorphs can be formed. Protein adsorption is a crucial step for the biological responses, involving, in particular, albumin, the most abundant blood protein. In this theoretical work, using molecular mechanics and molecular dynamics methods, the adsorption process of an albumin subdomain is reported both onto specific different crystallographic faces of TiO2 anatase and also on its ideal three-dimensional nanosized crystal, using the simulation protocol proposed in my previous theoretical studies about the adsorption process on hydrophobic ordered graphene-like or hydrophilic amorphous polymeric surfaces. The different surface chemistry of anatase crystalline faces and the nanocrystal topography influence the adsorption process, in particular the interaction strength and protein fragment conformation, then its biological activity. This theoretical study can be a useful tool to better understand how the surface chemistry, crystal structure, size and topography play a key role in protein adsorption process onto anatase surface so widely used as biomaterial.

Simulation of nanosizing effects in the decomposition of Ca(BH4)2 through atomistic thin film models

In this work, we model thin films of β-Ca(BH4)2 to understand how nanostructuration of the material can be an effective way to decrease the dehydrogenation enthalpy. Two different crystallographic faces of Ca(BH4)2 have been investigated (i.e., (001) and (101)), and two reaction pathways have been considered that release hydrogen through the formation of CaH2 and CaB6, respectively. Quantum mechanical calculations predict that size reduction from bulk to nanoscale leads to a sizeable decrease of the decomposition enthalpy of the borohydride of about 5 kJ/molH2. Therefore, the present results corroborate the evidence that nanostructured metal borohydrides show advantages for energy storage applications compared to their bulk counterparts.

Atomic structure and grain shape evolution of nanodiamond during annealing in oxidizing atmosphere from neutron diffraction and MD simulations

Real space pair-distribution function (PDF) analysis in conjunction with molecular dynamics (MD) simulations was applied to characterize crystal structure, shape and surface structure of diamond nanoparticles annealed in air up to 880 °C. MD simulated models of individual nanodiamond particles of various shapes and sizes were used to calculate theoretical radial distribution functions G(r) for powders with different grain size distributions. The calculated curves, showing distinct differences for the explored parameter space, were compared to the experimental G(r) functions obtained from neutron scattering for annealed detonated nanodiamond samples in a search for a model best describing the actual powders. It was found that as-synthesized nanodiamond grains are terminated by equally abundant (100), (110) and (111) crystallographic faces and their structure does not change upon annealing in air up to 280 °C. The shape and size of grains annealed above 480 °C changes due to surface etching. The etching rate differs between crystals faces and depends on temperature, resulting in the observed differences in grain shape. Below 680 °C the share of the (110) facets gradually increases and at 680 °C the grains become rhombic dodecahedra terminated solely by (110) surfaces. Further increase of the annealing temperature promotes formation of (111) surfaces and at 880 °C the preferred grain shape becomes an octahedron terminated by a variant of (111) surfaces possessing three dangling sp3 bonds per atom. At lower temperatures all grains become smaller and the size distribution moves towards the lower values. As the annealing temperature increases, the smallest grains disappear entirely and the average grain size grows back.

Cracking under Internal Pressure: Photodynamic Behavior of Vinyl Azide Crystals through N2 Release.

When exposed to UV light, single crystals of the vinyl azides 3-azido-1-phenylpropenone (1a), 3-azido-1-(4-methoxyphenyl)propenone (1b), and 3-azido-1-(4-chlorophenyl)propenone (1c) exhibit dramatic mechanical effects by cracking or bending with the release of N2. Mechanistic studies using laser flash photolysis, supported by quantum mechanical calculations, show that each of the vinyl azides degrades through a vinylnitrene intermediate. However, despite having very similar crystal packing motifs, the three compounds exhibit distinct photomechanical responses in bulk crystals. While the crystals of 1a delaminate and release gaseous N2 indiscriminately under paraffin oil, the crystals of 1b and 1c visibly expand, bend, and fracture, mainly along specific crystallographic faces, before releasing N2. The photochemical analysis suggests that the observed expansion is due to internal pressure exerted by the gaseous product in the crystal lattices of these materials. Lattice energy calculations, supported by nanoindentation experiments, show significant differences in the respective lattice energies. The calculations identify critical features in the crystal structures of 1b and 1c where elastic energy accumulates during gas release, which correspond to the direction of the observed cracks. This study highlights the hitherto untapped potential of photochemical gas release to elicit a photomechanical response and motility of photoreactive molecular crystals.