Submicron Crystals Research Articles

Reactive Noble-Gas Compounds Explored by 3D Electron Diffraction: XeF2-MnF4 Adducts and a Facile Sample Handling Procedure.

Recent advances in 3D electron diffraction (3D ED) have succeeded in matching the capabilities of single-crystal X-ray diffraction (SCXRD), while requiring only submicron crystals for successful structural investigations. One of the many diverse areas to benefit from the 3D ED structural analysis is main-group chemistry, where compounds are often poorly crystalline or single-crystal growth is challenging. A facile method for loading and transferring highly air-sensitive and strongly oxidizing samples at low temperatures to a transmission electron microscope (TEM) for 3D ED analysis was successfully developed and tested on xenon(II) compounds from the XeF2-MnF4 system. The crystal structures determined on nanometer-sized crystallites by dynamical refinement of the 3D ED data are in complete agreement with the results obtained by SCXRD on micrometer-sized crystals and by periodic density-functional theory (DFT) calculations, demonstrating the applicability of this approach for structural studies of noble-gas compounds and highly reactive species in general. The compounds 3XeF2·2MnF4, XeF2·MnF4, and XeF2·2MnF4 are rare examples of structurally fully characterized xenon difluoride-metal tetrafluoride adducts and thus advance our knowledge of the diverse structural chemistry of these systems, which also includes the hitherto poorly characterized first noble-gas compound, "XePtF6".

Compositional Analysis of Complex Mixtures using Automatic MicroED Data Collection.

Quantitative analysis of complex mixtures, including compounds having similar chemical properties, is demonstrated using an automatic and high throughput approach to microcrystal electron diffraction (MicroED). Compositional analysis of organic and inorganic compounds can be accurately executed without the need of diffraction standards. Additionally, with sufficient statistics, small amounts of compounds in mixtures can be reliably detected. These compounds can be distinguished by their crystal structure properties prior to structure solution. In addition, if the crystals are of good quality, the crystal structures can be generated on the fly, providing a complete analysis of the sample. MicroED is an effective method for analyzing the structural properties of sub-micron crystals, which are frequently found in small-molecule powders. By developing and using an automatic and high throughput approach to MicroED, and with the use of SerialEM for data collection, data from thousands of crystals allow sufficient statistics to detect even small amounts of compounds reliably.

Structure and absolute configuration of natural fungal product beauveriolide I, isolated from Cordyceps javanica, determined by 3D electron diffraction.

Beauveriolides, including the main beauveriolide I {systematic name: (3R,6S,9S,13S)-9-benzyl-13-[(2S)-hexan-2-yl]-6-methyl-3-(2-methylpropyl)-1-oxa-4,7,10-triazacyclotridecane-2,5,8,11-tetrone, C27H41N3O5}, are a series of cyclodepsipeptides that have shown promising results in the treatment of Alzheimer's disease and in the prevention of foam cell formation in atherosclerosis. Their crystal structure studies have been difficult due to their tiny crystal size and fibre-like morphology, until now. Recent developments in 3D electron diffraction methodology have made it possible to accurately study the crystal structures of submicron crystals by overcoming the problems of beam sensitivity and dynamical scattering. In this study, the absolute structure of beauveriolide I was determined by 3D electron diffraction. The cyclodepsipeptide crystallizes in the space group I2 with lattice parameters a = 40.2744 (4), b = 5.0976 (5), c = 27.698 (4) Å and β = 105.729 (6)°. After dynamical refinement, its absolute structure was determined by comparing the R factors and calculating the z-scores of the two possible enantiomorphs of beauveriolide I.

Influence of arylalkyl amines on the formation of hybrid CsPbBr3 nanocrystals via a modified LARP method.

Perovskite nanocrystals have attracted much attention in the last ten years due to their different applications, especially in the photovoltaic domain and LED performance. In this large family of perovskite nanocrystals, CsPbBr3 nanocrystals are attractive nanomaterials because they are good candidates for obtaining green emissions and exploring new synthesis routes. In this context, controlling the nanometric scale's morphology, particularly the size and monodispersity, is fundamental for exploring their photophysical properties and final applications. Currently, the nanometric size of nanocrystals is ensured by the presence of oleic acid and oleylamine molecules, in using Hot Injection (HI) or ligand-assisted reprecipitation (LARP) methods. If oleic acid plays a fundamental role, oleylamine can be easily substituted by other amino molecules, opening the way for the functionalization of CsPbBr3 nanocrystals and the obtention of new hybrid perovskite nanocrystal families. In this article, we describe the synthesis, by soft chemistry, of a new family of hybrid organic-inorganic CsPbBr3 nanocrystals, functionalized by aryl-alkylamine (AAA) molecules, through the modified LARP method. We highlight the mechanism for cutting submicron crystals into nanocrystals, using aryl-alkylamine molecules like scissors. The impact of these amino molecules on the final nanocrystals leads to different nanocrystal morphologies (nanocubes, nanosheets, or nanorods) and structures (monoclinic, rhombohedral, or tetragonal). In addition, this modified LARP method highlights, under certain experimental conditions, an unexpected formation of PbO ribbons.

Bismuth-based electrocatalytic scheme enabling efficient and selective electrosynthesis of 4-aminophenol in acidic media.

A highly efficient electrocatalytic platform based on in situ formed metallic bismuth submicron crystals (microBi) was developed for 4-aminophenol electrosynthesis via the electrochemical reduction of 4-nitrophenol at acidic pH. The facile formation and high reactivity of microBi enable efficient electrosynthesis of 4-aminophenol with high selectivity (∼100%) at the expense of an ultra-low overpotential.

Nanotrap Grafted Anionic MOF for Superior Uranium Extraction from Seawater.

On-demand uranium extraction from seawater (UES) can mitigate growing sustainable energy needs, while high salinity and low concentration hinder its recovery. A novel anionic metal-organic framework (iMOF-1A) is demonstrated adorned with rare Lewis basic pyrazinic sites as uranyl-specific nanotrap serving as robust ion exchange material for selective uranium extraction, rendering its intrinsic ionic characteristics to minimize leaching. Ionic adsorbents sequestrate 99.8% of the uranium in 120 mins (from 20,000 ppb to 24 ppb) and adsorb large amounts of 1336.8mg g-1 and 625.6mg g-1 from uranium-spiked deionized water and artificial seawater, respectively, with high distribution coefficient, Kd U ≥ 0.97 × 106 mL g-1 . The material offers a very high enrichment index of ≈5754 and it achieves the UES standard of 6.0mg g-1 in 16 days, and harvests 9.42mg g-1 in 30 days from natural seawater. Isothermal titration calorimetry (ITC) studies quantify thermodynamic parameters, previously uncharted in uranium sorption experiments. Infrared nearfield nanospectroscopy (nano-FTIR) and tip-force microscopy (TFM) enable chemical and mechanical elucidation of host-guest interaction at atomic level in sub-micron crystals revealing extant capture events throughout the crystal rather than surface solely. Comprehensive experimentally guided computational studies reveal ultrahigh-selectivity for uranium from seawater, marking mechanistic insight.

Making the Most of 3D Electron Diffraction: Best Practices to Handle a New Tool

Along with the adoption of three-dimensional electron diffraction (3D ED/MicroED) as a mainstream tool for structure determination from sub-micron single crystals, questions about best practices regarding each step along the workflow, from data collection to structure solutions, arise. In this paper, we discuss three particular aspects of a 3D ED/MicroED experiment which, after hundreds of structures solved in Rigaku’s laboratories, we have found to be important to consider carefully. First, for a representative model system of a hydrated compound (trehalose dihydrate), we show that cryo-transfer of the sample into the diffractometer is an effective means to prevent dehydration, while cooling of the sample without cryo-transfer yields a marginal improvement only. Next, we demonstrate for a small (tyrosine) and a large (clarithromycin) organic compound, how a simplified and fast workflow for dynamical diffraction calculations can determine absolute crystal structures with high confidence. Finally, we discuss considerations and trade-offs for choosing an optimal effective crystal-to-detector distance; while a long distance is mandatory for a protein (thaumatin) example, even a small molecule with difficult diffraction behavior (cystine) yields superior results at longer distances than the one used by default.

The grain size distribution of matrix in primitive chondrites

AbstractThe matrix of primitive chondrites is composed of submicron crystals embedded in amorphous silicates. These grains are thought to be the remains of relatively unprocessed dust from the inner regions of the protoplanetary disk. The matrix of primitive meteorites is often compared to chondritic porous interplanetary dust particles (CP‐IDPs) which are believed to be of cometary origin, having accreted in the outermost regions of the solar nebula. Crystalline grains in CP‐IDPs show evidence of a size–density relationship between the silicates and sulfides suggesting that these components experienced sorting prior to accretion. Here, we investigate whether such evidence of sorting is also present in the matrix constituents of primitive chondrites. We report findings from our study of grain size distributions of discrete silicate and opaque (sulfide and metal) grains within the matrix of the primitive meteorites Acfer 094 (C2‐ung.), ALHA77307 (CO3), MIL 07687 (C3‐ung.), and QUE 99177 (CR2). Mean radii of matrix silicate grains range from 103 nm in QUE 99177 to 2018 nm in MIL 07687. The opaque grains show a wider variation, with average radii ranging from 15 nm in QUE 99177 to 219 nm in MIL07687. Our results indicate that, in contrast to CP‐IDPs, the size distribution of matrix components of these primitive meteorites cannot be explained by aerodynamic sorting that took place prior to accretion. We conclude that any evidence of sorting is likely to have been lost due to a greater variety and degree of processing experienced on these primitive chondrites than on cometary parent bodies.

Sintering high-mechanical-properties microcrystalline PcBN by isothermal compression

Mechanical-performance of polycrystalline cubic boron nitride (PcBN) sintered using micron-sized powder particles might exceed that of samples produced from submicron crystals. However, no effective method has been found yet. In this study, commercial cubic boron nitride (cBN) powder (∼5 μm) was used to sinter high-performance PcBN without a binder. Two processes, isothermal compression (IC) and isothermal isobaric sintering (IIS), were used and compared. PcBN sintered with the former method possesses much more excellent mechanical performance, with the average Vickers hardness and indentation crack resistance of 73 GPa and 8.4 MPa·m1/2. The new temperature and pressure path adopted in the IC process can largely improve the hardness of PcBN sintered even with micro-sized powder. The quantitative analysis results of the defect structure in samples can be used as a reference for controlling the defect structure density to improve the material performance.

Characterization, biocompatibility and in vivo of nominal MnO2-containing wollastonite glass-ceramic

Abstract The present work pointed out the effect of adding different concentrations of MnO2 (0.25, 0.50, 1.00 and 2.00 wt%) on the structure and crystallization performance of wollastonite glass. Nominal MnO2-containing wollastonite glass was prepared with the addition of 10% Na2O to decrease the melting temperature through melt quenching technique. The thermal history of glasses indicated that the crystallization temperature was between 864 and 895°C. The heat treating of glasses at ∼900 and 1,100°C gave combeite (Na4Ca4Si6O18), rankinite (Ca3Si2O7), pseudowollastonite (Ca3Si3O9), bustamite (CaMnSi2O6) and cristobalite. The later sample densities increased with the incorporation of MnO2 from 1.88 to 2.24 g/cm3 concomitant with decrease of porosities from 32.59 to 20.83%. The microstructure showed nano-size crystals in rounded, angular or irregular micro-size clusters, whereas after soaking in simulated body fluid for 1 month showed submicron crystals of carbonated calcium phosphate phase. Both fourier transform infrared spectroscopy and scanning electron microscopy/energy dispersive X-ray delineated the samples’ biocompatibility. Also, the negative zeta potential results enabled bone cell activity. Moreover, the bone healing with complete mineralization was remarked in case of the in vivo implantation of the G0.50 group. These results can be of a great significance in the application of MnO2-containing combeite, rankinite phases for bone treatment and biomedical applications.

Excitation-Dependent Photoluminescence of BaZrO3:Eu3+ Crystals.

The elucidation of local structure, excitation-dependent spectroscopy, and defect engineering in lanthanide ion-doped phosphors was a focal point of research. In this work, we have studied Eu3+-doped BaZrO3 (BZOE) submicron crystals that were synthesized by a molten salt method. The BZOE crystals show orange–red emission tunability under the host and dopant excitations at 279 nm and 395 nm, respectively, and the difference is determined in terms of the asymmetry ratio, Stark splitting, and intensity of the uncommon 5D0 → 7F0 transition. These distinct spectral features remain unaltered under different excitations for the BZOE crystals with Eu3+ concentrations of 0–10.0%. The 2.0% Eu3+-doped BZOE crystals display the best optical performance in terms of excitation/emission intensity, lifetime, and quantum yield. The X-ray absorption near the edge structure spectral data suggest europium, barium, and zirconium ions to be stabilized in +3, +2, and +4 oxidation states, respectively. The extended X-ray absorption fine structure spectral analysis confirms that, below 2.0% doping, the Eu3+ ions occupy the six-coordinated Zr4+ sites. This work gives complete information about the BZOE phosphor in terms of the dopant oxidation state, the local structure, the excitation-dependent photoluminescence (PL), the concentration-dependent PL, and the origin of PL. Such a complete photophysical analysis opens up a new pathway in perovskite research in the area of phosphors and scintillators with tunable properties.

Glass-Ceramics from Trachyte Rock- Limestone or Magnesite

Inexpensive sintered glass-ceramic glaze was prepared from a mixture of Egyptian trachyte with either limestone or magnesite. A represented trachyte rock was pulverized to powder (<0.083 mm) and also both limestone and magnesite. The well mixed batches were melted near 1450 °C/3 h temperature then the glass melt was quenched in water, dried, pulverized to powder and finally shaped in moulds. The sintering process of the pre-shaped glasses, within 1000-1100 °C range, gave augite and olivine in case of trachyte-magnesite whereas wollastonite and Ca-olivine in case of trachyte-limestone. However, cristobalite was developed in both cases. The microstructures in both cases showed glassy matrix scattered with submicron and nano-size crystals either in irregular shape in case of trachyte-limestone or clear crystals in case of trachyte-magnesite. The densities of the sintered samples were in the range of 2.36 and 2.57 g/cm3 in case of the trachyte-limestone and 2.36 and 2.64 g/cm3 in case of the trachyte-magnesite. The coefficient of thermal expansion (CTE) and the hardness of the sintered glass-ceramic were in the range of 6.2-8.5 × 10−6 °C−1 and 440-563 GPa respectively. However, the CTE values decreased in case of trachyte-limestone whereas the hardness values were high in case of trachyte-magnesite. The present glass-ceramic samples had porcelain nature and could be used in cladding of wall and floor.

Calcite Kinetics for Spiral Growth and Two-Dimensional Nucleation.

Calcite crystals grow by means of molecular steps that develop on {10.4} faces. These steps can arise stochastically via two-dimensional (2D) nucleation or emerge steadily from dislocations to form spiral hillocks. Here, we determine the kinetics of these two growth mechanisms as a function of supersaturation. We show that calcite crystals larger than ∼1 μm favor spiral growth over 2D nucleation, irrespective of the supersaturation. Spirals prevail beyond this length scale because slow boundary layer diffusion creates a low surface supersaturation that favors the spiral mechanism. Sub-micron crystals favor 2D nucleation at high supersaturations, although diffusion can still limit the growth of nanoscopic crystals. Additives can change the dominant mechanism by impeding spiral growth or by directly promoting 2D nucleation.

Metallic Copper (Cu[0]) Obtained from Cu2+-Rich Acidic Mine Waters by Two Different Reduction Methods: Crystallographic and Geochemical Aspects

The recovery of valuable metals from different types of wastes has become of prime strategic interest given the scarcity of primary critical raw materials at international scale. Implementation of new methods or refinement of classical techniques with modern technological advances is, therefore, an active research field. Mine wastes are of special interest because their high metal concentrations make them environmentally harmful and economically profitable at the same time. In this study, we evaluated two different methods of Cu recovery from extremely acidic mine waters seeping from wastes and abandoned mines in SW Spain. Through a series of different batch experiments, we compared the method efficiency and crystallographic properties of elemental copper (Cu[0]) obtained by reduction of Cu2+ ions by (1) chemical reduction using ascorbic acid at different environmental conditions of pH (1.50–3.95), temperature (25–80 °C) and ascorbic acid concentration (10 mM to 0.1 M), and (2) classical cementation method with scrap iron at pH 1.50 and 25 °C. Our study demonstrates that the precipitation of Cu[0] can take place at pH 3.95 and low AA concentrations (0.1 M), resulting in large (µm-scale), perfectly developed crystals of copper with pseudoprismatic to acicular habit after 24 h of aging, likely through formation of a transient compound consisting in Cu2+-ascorbate and/or cuprite (Cu2O) nanocolloids. Reduction experiments at higher AA concentrations (0.1 M) showed faster precipitation kinetics and resulted in high-purity (&gt;98%) copper suspensions formed by subrounded nanoparticles. The AA method, however, yielded very low recovery rates (15–25%) because of the low pH values considered. The cementation method, which produced tree-like aggregates formed by sub-micron crystals arranged in different directions, proved to be much more efficient (&gt;98% recovery) and cost-effective.

Ultrafast synthesis of discrete submicron AlPO4-LTA molecular sieve crystals and their application in molecular sieve membrane

Ultrafast synthesis of nanosized and submicron zeolite materials is challenging but highly desired due to their wide applications. Herein, discrete LTA-type aluminophosphate molecular sieve (AlPO4-LTA) submicron crystals have been synthesized in an open glass beaker under oil bath heating for only 10 min. The influences of the synthesis parameters, including the ratios of tetramethylammonium hydroxide (TMAOH)/Al and HF/Al, and the heating methods were investigated thoroughly. The optimized product exhibits exceptional properties, including good crystallinity, small particle size (ca. 130 nm) and large BET surface areas (867 m2/g). The time-dependent study reveals the formation process of submicron AlPO4-LTA crystals: the primary worm-like amorphous first aggregated into loosely assembled spheres, then the crystallinity of the spheres enhances while keeping the particle size unchanged. Using the submicron AlPO4-LTA crystals as the seed layer, an AlPO4-LTA membrane was synthesized via secondary growth approach. For binary mixtures at 298 K, the separation factors for H2/N2, H2/O2, H2/CO2 and H2/CH4 are 4.8, 6.2, 7.3 and 5.9, respectively, suggesting the good gas separation performance of the membrane.

Yb-doped Y–Al–O thin films with a self-organized columnar structure and their anti-Stokes photoluminescence properties

We fabricated ytterbium-doped yttrium aluminum oxide (Yb:Y–Al–O) thin films by radio-frequency magnetron sputtering and evaluated their crystallinity and anti-Stokes photoluminescence (PL) properties for optical refrigeration. The Yb:Y–Al–O films that were grown on c-sapphire substrates had better transparency than the films deposited on fused-quartz substrates. The better transparency is considered to be a result of the smaller mismatch between the thermal expansion coefficients of Yb:Y–Al–O and c-sapphire. We found that the thin films on the c-sapphire substrates consist of densely packed sub-micron columnar crystals that are aligned perpendicular to the substrate. In these films, we confirmed the existence of perovskite, garnet, and monoclinic phases despite using a single-phase sputtering target. The excitation wavelength dependence of anti-Stokes PL is used to investigate the energy transfer process between trivalent Yb ions in neighboring columnar crystals. The data indicate that the resonant energy transfer from Yb3+ ions at a specific seven-coordinated site of the monoclinic phase to Yb3+ ions in neighboring columnar crystals is faster than the radiative relaxation at the energy-donor site.

Influence of the microstructure on mechanical properties of SLM additive manufacturing Fe-based bulk metallic glasses

Fe-based bulk metallic glass (BMG)(FeCrMoWMnSiBC) was produced by selective laser melting (SLM) successfully in this study. The best parameters were determined through extensive experiments. The relative density (95%) and amorphous rate (95.47%) samples were obtained by this parameter. The analysis of the microstructure reveals that the crystalline phases in the heat affected zone (HAZ) are mainly α-Fe and M23(CB)6 phases, and co-exist with the amorphous phases. The Heat treatment is employed to study the crystallization behavior of amorphous phases. The α-Fe phase, as the primary phase, grows into a submicron crystal phase under the action of multiple thermal cycles. Nanoindentation test results show that the hardness of the amorphous phase is higher than that of the nano-grain region, and the hardness of the nanocrystalline region is higher than that of the submicron-grain region. The free volume content is different and the amorphous phase is not uniform due to the complex thermal cycle. The maximum hardness occurs in the amorphous phase with 22.6 GPa.

Multichannel emissions from 5DJ metastable levels of Eu3+ in miscible-phase phosphors

BaYF5: Eu3+-fluorophosphate (BYF: E-FP) miscible-phase phosphors with tunable white fluorescence and high color-rendering index (CRI) are synthesized by blending Ba(Y1−xEux)F5 (BYF: E) submicron crystals (SCs) into fluorophosphate glass. Adjusting the concentration of Eu3+ purposefully, the comparable intensity of blue, green and red components by multichannel emissions can be regulated to achieve the adjustable white light. The quantum efficiency of 5D0 level in Eu3+ reaches up to 90.8%, and the millisecond fluorescence lifetime of blue and green emissions from 5D1, 5D2 and 5D3 levels exhibit the effectiveness of metastable levels. In coordination with blue emission from Sn2+, the color coordinates of BYF: E-FP are concentrated in white region of chromaticity diagram and its CRI is able to reach as high as 86. Tunable white fluorescence and high CRI indicate that miscible-phase phosphors possess promising applications in optoelectronic lighting.

One-step, low temperature synthesis of reduced graphene oxide decorated with ZnO nanocrystals using galvanized iron steel scrap

Production of a ZnO–rGO composite, using a novel one-pot method consisting in continuously flowing argon into a GO aqueous suspension heated at 80 °C, in the presence of galvanized iron steel scrap is presented. FTIR shows the complete disappearance of GO functional groups and only the C=C band remained, indicating extensive GO reduction. Raman spectra indicated sp2 character increase after reaction and the presence of the E2h mode of ZnO. SEM showed submicron crystals identified by XRD as ZnO in the hexagonal phase, while TEM images indicate ZnO nanoparticles decorate mainly the rGO borders. Optical band gap of 3.5 eV corresponding to ZnO, and optical transitions at 4.1 and 5.5 eV related with n → π and π → π* were observed. Electrochemical characterization by cyclic voltammetry shows an specific capacitance of 4.7 F g−1 at a scan rate of 5 mVs−1, which drops to ca. 0.8 F g−1 at 200 mVs−1. By electrochemical impedance spectroscopy, the relaxation time was ca. 5 ms. The proposed mechanism for the materials‘ synthesis includes Zn dissolution from scrap, galvanic displacement of oxygen moieties at the GO sheet, Zn deposition onto the carbon surface, and further oxidation and growth of ZnO nanocrystals.

Electrochemical epitaxial (200) PbSe submicron-plates on single-layer graphene for an ultrafast infrared response

In suit epitaxial growth of highly oriented PbSe submicron crystals on graphene via ECALE method. The hybrid PbSe/graphene structure presents a fast response and outstanding photoresponsivity under illumination of 2.7 μm light at room temperature.