Crystal Patterns Research Articles

Fluorescent and electronic properties of Dysprosium acylpyrazolone complexes along with their synthesis and structural features

Six distorted square antiprismatic eight coordinated Dysprosium acylpyrazolone complexes were synthesized having the compositions [Dy(L1)3(EtOH)(H2O)] (DyL1), [Dy(L2)3(EtOH)(H2O)] (DyL2), [Dy(L3)3(EtOH)(H2O)] (DyL3), [Dy(L4)3(EtOH)(H2O)] (DyL4), [Dy(L5)3(EtOH)(H2O)] (DyL5), and [Dy(L6)3(H2O)(EtOH)] (DyL6). The structure of all six complexes was examined using ESI-mass, FT-IR, UV–Vis, powder XRD, and thermogravimetric methods. According to the single crystal analysis of DyL4A, the complex was found eight coordinated (DyO8) with a distorted square antiprismatic geometry. The comparison of stimulated powder pattern of DyL4A crystal and experimental powder x-ray data helps to confirm the geometry of other complexes. In the solid-state emission spectra, the transition 4F9/2→6H13/2, which is close to the yellow region of the visible spectrum (∼510–530 nm), exhibits hypersensitivity. The variance in intensity between electric-dipole and magnetic-dipole transition suggests a less asymmetric environment. The solvent effect has been thoroughly investigated through a comparative analysis of electronic spectra in different solvents. The intensity of emission spectra, Y/B ratio, and antenna effect energy diagram were examined from solid-state emission spectra.

Effect of extraction methods on the chemical, structural, and rheological attributes of fructan derived from Arctium lappa L. roots

The focus of this study was the evaluation of how extraction techniques impact the chemical, structural, and rheological attributes of fructans extracted from Arctium lappa L. roots. Three distinct extraction procedures were used, utilizing water as solvent, infusion extraction conducted at ambient temperature (25 °C for 5 min), thermal extraction employing reflux (100 °C for 2 h), and ultrasound-assisted extraction (50 °C for 1.38 h with a 158 W output). Chemical characterization by Nuclear Magnetic Resonance (NMR) and colorimetric analyses revealed the obtaining of inulin-type fructans (yield 83 %). The degree of polymerization (DP) was found to be the lowest for ultrasound-assisted extraction (14.38), followed by the room-temperature (20.41) and thermal (21.14) extraction techniques. None of the extraction techniques appeared to modify the molecular structure of the isolated compounds. In X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses, distinct crystallization patterns were observed for the room-temperature and thermal extraction techniques, though all fractions consistently exhibited characteristic bands of inulin-type fructan. Rheological assessments indicated a viscoelastic nature of the fractions, with those extracted thermally demonstrating a greater viscosity. This study shows that the choice of extraction method can influence the structural characteristics of inulin-type fructans derived from the burdock root.

Samarium addition-mediated simultaneous achievement of excellent resistance drift and superior thermal stability in phase-change compound antimony-selenium thin film

The Sm-doped Sb7Se3 thin films were systematically investigated, including phase change behavior, phase structure, microstructure, and electrical properties. The in-situ resistance test displays that the addition of Sm element leads to a significant increase in the crystallization temperature, decadal data retention and crystallization activation energy, implying better thermal stability. Crystallization kinetic analysis indicates a one-dimensional growth crystallization pattern, exhibiting an ultra-fast crystallization speed. The change in optical bandgap reflects that the exotic Sm atoms enhance the bandgap energy, which facilitates the reduction of the threshold current. Resistance drift test highlights the suppression of structural relaxation by Sm atoms, which would greatly improve the reliability of the information readout. X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectra, and transmission electron microscopy demonstrate that the addition of Sm retards the crystallization process and refines the grain size. Energy dispersive spectroscopy shows that the Sm dopant has incorporated into Sb7Se3 thin film. The phase change memory cell based on Sm-doped Sb7Se3 film exhibits faster running speed (100 ns) and lower power consumption (3.0 × 10−11 J) than the conventional Ge2Sb2Te5 material. All the results prove that incorporating appropriate amounts of Sm into Sb7Se3 material is an ideal technique for optimizing resistance drift and thermal stability of Sb7Se3 thin films.

Light-driven nucleation, growth, and patterning of biorelevant crystals using resonant near-infrared laser heating

Spatiotemporal control over crystal nucleation and growth is of fundamental interest for understanding how organisms assemble high-performance biominerals, and holds relevance for manufacturing of functional materials. Many methods have been developed towards static or global control, however gaining simultaneously dynamic and local control over crystallization remains challenging. Here, we show spatiotemporal control over crystallization of retrograde (inverse) soluble compounds induced by locally heating water using near-infrared (NIR) laser light. We modulate the NIR light intensity to start, steer, and stop crystallization of calcium carbonate and laser-write with micrometer precision. Tailoring the crystallization conditions overcomes the inherently stochastic crystallization behavior and enables positioning single crystals of vaterite, calcite, and aragonite. We demonstrate straightforward extension of these principles toward other biorelevant compounds by patterning barium-, strontium-, and calcium carbonate, as well as strontium sulfate and calcium phosphate. Since many important compounds exhibit retrograde solubility behavior, NIR-induced heating may enable light-controlled crystallization with precise spatiotemporal control.

A novel non-centrifugal sugar prepared from tiger nut (Cyperus esculentus L.) meal: Preparation methods and comparison with sugarcane

The lack of research on the rich sucrose in tiger nut meal has been a major obstruction to the comprehensive utilization of tiger nut (Cyperus esculentus L.). In this study, for the first time, tiger nut meal was used to producing non-centrifugal sugar (NCS). Three samples − NCS-W1 (NCS prepared by water extraction and concentrated at 115 °C), NCS-W2 (NCS prepared by water extraction and concentrated at 135 °C), and NCS-E (NCS prepared by 70 % ethanol–water extraction and concentrated at 115 °C) were obtained, with yields of 14.25–14.59 %. These samples and sugarcane NCS products (NCS-C1, NCS-C2, NCS-L) were compared and analyzed in terms of color, pH, turbidity, soluble solid content, and proximate composition. Their Fourier-transformed infrared spectra, crystal patterns, and thermal stabilities were also analyzed. The NCS-W1, -W2, and -E showed excellent performance, and they were better than sugarcane NCS products in terms of free radical scavenging ability and cytoprotective effects. Differences in phenolic acid composition, flavonoid composition, amino acid, mineral content, and vitamins C and E content were also analyzed. This work demonstrates that tiger nut meal might be a new source of NCS. As such it would contribute to the full utilization of tiger nut.

Activated Single Photon Emitters And Enhanced Deep‐Level Emissions in Hexagonal Boron Nitride Strain Crystal

AbstractThe peculiar defect‐related photon emission processes in 2D hexagonal boron nitride (hBN) have become a topic of intense research due to their potential applications in quantum information and sensing technologies. Here, it is reported on exotic single photons and enhanced deep‐level emissions in 2D hBN strain crystal, which is fabricated by transferring multilayer hBN onto hexagonal close‐packed silica spheres on a silica substrate. Effective activation of single photon emission is realized from the defect ensembles in the multilayer hBN at positions that are in contact with the apex of the SiO2 spheres. At these points, the local tensile strain‐induced overall blue shift of the SPE ensembles is up to 12 nm. Furthermore, high spatial resolution cathodoluminescence measurements show remarkable strain‐enhanced deep‐level emissions in the multilayer hBN with the emission intensity distribution following the periodic hexagonal pattern of the strain crystal. The maximum deep‐level emission enhancement is up to 350% with an energy redshift of 6 nm. These results provide a simple on‐chip compatible method for activating and tuning the defect‐related photon emissions in multilayer hBN, demonstrating the potential of hBN strain crystal as a building block for future on‐chip quantum nanophotonic devices.

Narsarsukite in peralkaline granites from the Papanduva Pluton, Graciosa Province, south Brazil: Insights from textural and compositional features

AbstractWe report textural and compositional data for the titanosilicate narsarsukite [Na2(Ti,Fe3+)Si4(O,F)11] in peralkaline granites from the Papanduva Pluton in Graciosa Province, south-southeastern Brazil. Two distinct narsarsukite generations, one late magmatic and the other post-magmatic, were identified on the basis of textural and compositional features. The magmatic generation consists of larger, euhedral to subhedral variably zoned crystals and late poikilitic intergrowths between narsarsukite and albite laths, representing the crystallisation of the latest melt pockets. The post-magmatic generation forms smaller, typically fibrous crystals and irregular aggregates that occur interstitially or replace the primary mafic minerals, particularly arfvedsonite. Compositions of narsarsukite from the Papanduva Pluton cover most of the compositional range described in known occurrences. The magmatic generation is enriched in Zr and depleted in Al. The Fe3+ and Al contents show a positive correlation for the magmatic crystals, but a negative correlation for the post-magmatic narsarsukite. The Al/Fe3+ ratios are higher in the post-magmatic crystals and can be used to discriminate between the two generations. The compositional variations are controlled mainly by the heterovalent substitution (Ti, Zr)4+ + O2– = (Al, Fe)3+ + F1–, and are compatible with (OH)1– ions in the O site. Narsarsukite has significantly higher concentrations of mid REE+Y and HFSE and very low to absent contents of LREE and LILE relative to the host-rocks. The average REE pattern of the magmatic crystals is highly fractionated, consistent with the expected strong preference for the smaller HREE. The post-magmatic crystals that replace arfvedsonite have flatter patterns, with higher concentrations of LREE and MREE. Their compositions suggest a fluid phase relatively rich in HFSE, REE, Y, Pb, Th and U. Narsarsukite is a common phase in strongly peralkaline granites such as the Papanduva Pluton and the well-known Strange Lake Complex, and should be considered a diagnostic mineral of highly peralkaline SiO2-oversaturated rocks containing rare Ti and Zr mineral assemblages.

Coupling effects of human serum albumin and sodium chloride on biological desiccation patterns

Desiccation patterns of plasma sessile drops have attracted increasing attention, not only because of the fantastic underlying physics, but also due to their potential of being health diagnostic tools. However, plasma is a multicomponent system, which contains macromolecular proteins and inorganic salts; these components have complicated interactions to define pattern morphologies. Unfortunately, mechanisms of coupling effects of main components on pattern morphologies are still not clear, thus limiting their diagnostic applications. Here we show the coupling effects of human serum albumin (HSA) and sodium chloride (NaCl) on plasma desiccation patterns. Our experiments indicate that NaCl enhances the “coffee ring” effect of HSA to promote its aggregation at the peripheral region and narrows down its aggregation area; this would influence the distribution of internal stresses, resulting in a larger number of radial cracks, with a larger width but a shorter length, than cracks in pure HSA. In the meantime, HSA experiences the gelation process that propagates from the peripheral region to central region and causes the spatiotemporal deviation in the degree of solidification, which induces a higher concentration of NaCl in the central region, thus leading to the formation of crystal patterns. Our further experiments demonstrate that these characteristic patterns are correlated to the variation in the concentration of NaCl, which can be caused by hyponatremia and hypernatremia in real biofluids. Our findings not only provide a new mechanistic insight into biological desiccation patterns, but also bridge the gap between the understanding and diagnostic applications of these desiccation patterns.

Physicochemical and Functional Properties of Banana Starch and Its Alternative Returns

The current study’s goal is to isolate the starch from different varieties of banana i.e. Local Banana (LB) and BARI Banana2 (BB2)and characterize them in order to explore their physical and chemical compositions, amylose content, resistant starch content, functional properties, granule morphology and crystalline pattern. Different techniques were used for characterization viz. X-ray diffractometery (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Spectroscopy (SEM) etc. The starch extracted from banana showed significant difference in the amylose content and the value was found 28.26%and 25.93%respectively for local banana starch (LBS) and bari banana 2 starch (BB2S). This study also revealed that selected banana varieties can be a potential source for the production of resistant starch. The resistant starch (RS) content of the banana was found 46.93% and 45.78% respectively for LBS and BB2S. Using de-branching and autoclaving technique in the starch, there was a significant increase in RS content. Paste clarity was decreased gradually with time for all the starch samples. Water absorption capacity (WAC) and oil absorption capacity (OAC) of LBS and BB2Swere found in the ranged of 165.8-170.7% and 132.6-168.1% respectively. XRD showed both LB and BB2 starches had B-type crystal pattern. The d-spacing of banana starches were ranged from 3.86-5.88Á. SEM data revealed that banana starches possessed the regular elongated round ridges with smooth surface in the range of 4.3-12.4 µm. The information obtained from this research indicates that both banana starches can be used in different areas; especially in food, pharmaceutical and cosmetics industries as an edible coating, thickening agent, fat replacer, etc. Also, banana starch containing functional food can be recommended for diabetic patients.

Synthesis of Nanomagnetite/Crosslinked Carboxymethyl kappa Carrageenan Nickel Imprinted Composite

Nickel(II) ions are carcinogenic water pollutants. To increase the accuracy of instrumental analysis of Ni(II) content, several analytical preparation methods have been developed, including solid phase adsorption extraction. The development of magnetic solid phase extraction adsorbents for metal ions is required, to support the application of magnetic solid phase adsorption as a method of separating metal ions in aqueous samples. This research describes the synthesis of Magnetic Solid Phase Extraction adsorbents as Ni(II) ion adsorbents, nano magnetite/carboxymethyl kappa-carrageenan (CMKC) crosslinked bisphenol A diglycidyl ether (BADGE) imprinted Ni(II)-IIP ion composites. This research was carried out in several stages, synthesis and characterization of nano magnetite (NM), synthesis and characterization of CMKC, and synthesis of NM/CMKCNi(II)-IIP adsorbents. The results of the synthesis were analyzed for morphological characteristics, magnetic strength, spectral characteristics, crystallinity, and composition using SEM, FTIR, XRD, and XRF instruments. The adsorption ability of Ni(II) of the adsorbent was tested. Determination of Ni(II) ion content in the sample before and after adsorption was carried out using a flame atomic absorption spectrophotometer (FAAS). Based on the results of spectral character analysis, crystal diffraction patterns, magnetic strength, and morphology, it is confirmed that nano-magnetite has been successfully synthesized. The diameter of the nano magnetite grains is 21.8 nm, the adsorbent NM/CMKCNi(II)-IIP has magnetic properties and wavy surface morphology. The optimum adsorption ability of Ni(II) for the NM/CMKCNi(II)-IIP composite was 2.44 mg Ni(II)/g adsorbent. To evaluate the tendency of the adsorption ability of the adsorbent towards Ni(II) ions in the presence of competitor ions, the adsorption ability of the adsorbent to adsorp Ni(II) ions in samples containing Ni(II) ions, Pb(II) ions and a mixture of Ni(II) ions. and Pb(II) were determined, based on the results of the analysis, the ability of the adsorbent to adsorb Ni(II) ions was higher than the ability of the adsorbent to adsorb Pb(II) ions, in all types of samples.

Crystal Structure, quantum chemical analysis and apoptotic propensity of diaryl substituted α-aminophosphonates as selected C[sbnd]P bonded systems

Three component Kabachnik-Fields reaction under sonochemical conditions was utilized for synthesizing library of electronically diverse aryl substituted α-aminophosphonates as representative carbon phosphorus bonded systems. Single crystal X-ray structures of four novel α-aminophosphonate derivatives with comprehensive Hirshfeld surface analysis for highlighting influence of different functionalities over α-aminophosphonate motif on the crystal packing pattern and formation of molecular assemblies via supramolecular aggregation have been presented. Solid state absorption and photoluminescence studies corroborated electronic and crystal packing influences. The computational methodologies for evaluating quantum chemical descriptors of electronic properties of α-aminophosphonates were bench marked. The bioactivity potential of synthesized library of α- aminophosphonates was evaluated from their cytotoxic propensity towards human cancer lines in NCI-60 panel via SRB assay. The screened derivatives showed a range of cytotoxicity against cancer cell lines in NCI-60 panel. Compound 3 exhibited highest cell growth inhibition in prostate cancer cells with IC50 value of 10.94 μM. For mechanistic insights apoptotic propensity was evaluated using caspase-3 enzyme assay in PC-3 cells. The onset of apoptosis via caspase-3 activation was evidenced as a major pathway from morphological changes under fluorescence microscope with and without DAPI staining. The triggering of apoptosis via caspase 3 activation by the lead compound 3 was also confirmed from western blot analysis of PARP-1 in PC-3 cancer cells. Furthermore, the anti-metastatic potential of compound 3 can be predicted from its efficacy in restricting the migration of PC-3 cancer cells under in vitro conditions observed from wound healing assay.

Crystallization and vitrification of solutions with weak intermolecular interaction of the components

An experimental study of the phenomenon of cluster crystallization and vitrification of solutions with weak intermolecular interaction of the components was performed with use of a purposely developed method of microvolumetric scanning tensodilatometry. Volumetric effects accompanying cooling and subsequent heating of aqueous solutions of glycerol and dimethyl sulfoxide were recorded within temperature range 300…135 K, and they are completely in line with patterns of cluster crystallization. The same phenomenon was used to analyze the structure of amorphous fractions of such solutions. Formation inside of them of ice nanocrystals without breakage of hydrogen bonds between water molecules and molecules of cryoprotectant dramatically reduces stability of amorphous fractions. Based on the resulted tensodilatograms, state diagrams for solutions, which include cluster phase, were for the first time plotted.

Void space and cavity measurement of the prepared zeolite y using X-ray diffracting modelling

Zeolite was synthesized using a solitary gel technique with Iraqi kaoline. Zeolite 's specific structural nature makes it difficult to use X-ray diffraction (XRD) to evaluate a single crystalline characteristic. Structural analysis to estimation and visualization of one crystal geometric properties by CrystalMaker software was carried out using XRD and the simulation of a crystal pattern using a Rietveld refinement technique using Maud software. This paper describes the Crystal Maker software suite, which includes the visualization, modelling and diffraction simulation of modular programs for crystal and molecular structures. The fundamental reasoning for the program is explored and a variety of applications are given for teaching and research in crystal chemistry and molecular dynamics.

Synthesis of xCe-MnO2 with three-dimensional ultra-thin nanosheet structure and its excellent low-temperature reducibility for toluene catalysis.

A series of xCe-MnO2 (x = 0-1) catalysts were synthesized using ammonium oxalate as a precipitator via the redox precipitation method and hydrothermal synthesis method. The results indicate that 0.25Ce-MnO2 exhibited the highest catalytic activity for toluene oxidation, with the T99 of 240°C. Characterization results from XRD, Raman, SEM, TEM, EDS-mapping, BET, and other techniques reveal that the 0.25Ce-MnO2 catalyst exhibited a three-dimensional multistage ultrathin nanosheet structure by adjusting the introduction amount of Ce, with abundant active sites, and effectively formed Ce-Mn homogeneous dispersion. The larger pore size and volume of 0.25Ce-MnO2 catalyst lead to it excellent toluene transfer ability. Furthermore, compared with MnO2, the crystal pattern of 0.25Ce-MnO2 shifted to the tetragonal cryptomelane type α-MnO2 phase and exposed more crystal planes which are beneficial to catalyze toluene. H2-TPR, O2-TPD, and XPS characterization further confirmed the strong interaction between Ce and Mn oxides, which exhibited better low-temperature reducibility and oxygen migration, along with abundant Ce3+ and Mn3+ species, where lattice oxygen played a major role. Moreover, in situ DRIFTS revealed that the 0.25Ce-MnO2 catalyst showed higher adsorption and desorption capacity for toluene than the MnO2 catalyst, and benzoate species were the key intermediates for catalytic oxidation. Additionally, benzoate and surface phenolic species were the key intermediates for catalytic oxidation of MnO2. Because 0.25Ce-MnO2 possesses better ability of converting toluene to benzoate species, it exhibits better activity.

Oxygen sensing behavior modulation of tetranuclear copper iodide hybrid materials using ligand engineering

Copper iodide hybrid materials (CIHMs) are receiving great attention as promising luminescent materials. Their structural diversity can be enriched by design and selection of organic ligands, associated with corresponding photophysical properties. However, the role of ligands in modulating sensing performance of CIHMs stays rarely revealed. Here, we demonstrate the O2 sensing capability of four tetranuclear CIHMs and reveal the impact of ligands on their different triplet quenching process. Oxygen sensing films were prepared using the selected CIHMs. The study results reveal their oxygen sensing behaviors with wide linear photoluminescence (PL) responses in the range from 0% to 100% for gaseous oxygen, and the corresponding PL quenching ratios of 12.14, 11.30, 2.90 and 2.26 (0–100% O2), respectively. In addition, all the CIHMs showed rapid and reversible response to oxygen within 10 s. Through investigating the time-resolved luminescence spectra, 1H NMR and corresponding crystal structures of the CIHMs in N2 and O2 environments, we highlight that specific crystal stacking patterns caused by different ligands play a major role in their distinct oxygen sensing behaviors. It indicates that the sensing performance of the CIHMs can be regulated through functionalization of the ligands which inspires new insights into their more extensive application.

Thermal performance of a laser-diode end-pumped Nd:YVO4 slab crystal cooled by a pair of microchannel heat sinks

Laser crystal is a key component in the all solid-state laser system. The cooling method for the laser crystal is quite critical when the pump power is high. However, due to some measurement difficulties, the surface temperature and heat dissipation pattern of the laser crystal have not been well demonstrated previously. In this work, we use a pair of novel central-jetting microchannel heat sinks (CJ-MCHSs) to cool a Nd:YVO4 slab crystal under high-power pump conditions. The surface temperature of the crystal is measured directly from its side face by using a slot barrier to filter stray light from pump radiation. The temperature distribution and local heat flux of the laser crystal are obtained. It shows that the surface temperature of the slab crystal decreases linearly along the beaming depth. At a typical pump power of 276 W, the temperature reaches 136 °C at the front face of the crystal but it is only 58 °C at the end face. The crystal's thickness affects the rate of heat dissipation. When the crystal's thickness increases from 1.0 mm to 1.5 mm, the temperature of the crystal is enhanced by about 15 °C. In the present experiments, the surface temperature of the CJ-MCHS is also monitored. The front side and back side of the CJ-MCHS show quite different temperature distribution patterns because of the non-uniform heat releasing pattern of the crystal. Comparing with a traditional macrochannel heat sink, the novel CJ-MCHS reduces the temperature gradient along the beaming direction and eliminates the unsymmetrical temperature distributions at the sides of the crystal.

Fabrication of CNTs-reinforced poly(vinyl alcohol) nanocomposite film with tailored structural, surface chemical and optical properties

Purpose This study aims to fabricate multiwalled carbon nanotubes (MWCNTs)-mediated polyvinyl alcohol (PVA) composite films using the solution casting approach. Design/methodology/approach The prepared films were evaluated for diverse structural, surface, optical and electrical attributes using advanced analytical techniques, i.e. electron microscopy for surface morphology, Fourier transform infrared spectroscopy for tracing chemical functionalities, x-ray diffraction (XRD) for crystal patterns, water contact angle (WCA) analysis for surface wettability and UV visible spectroscopy for optical absorption parameters. The specimens were also investigated for certain rheological, mechanical and electrical properties, where applicable. Findings The surface morphology results expressed a better dispersion of MWCNTs in the resultant PVA-based nanocomposite film. The XRD analysis exhibited that the nanocomposite film was crystalline. The surface wettability analysis indicated that with the inclusion of MWCNTs, the WCA of the resultant nanocomposite film improved to 89.4° from 44° with the pristine PVA film. The MWCNTs (1.00%, w/w) incorporated PVA-based film exhibited a tensile strength of 54.0 MPa as compared to that of native PVA as 25.3 MPa film. There observed a decreased bandgap (from 5.25 to 5.14 eV) on incorporating the MWCNTs in the PVA-based nanocomposite film. Practical implications The MWCNTs’ inclusion in the PVA matrix could enhance the AC conductivity of the resultant nanocomposite film. The prepared nanocomposite film might be useful in designing certain optoelectronic devices. Originality/value The results demonstrated the successful MWCNTs mediation in the PVA-based composite films expressed good intercalation of the precursors; this resulted in decreased bandgap, usually, desirable for optoelectronic applications.

Size-dependent miscibility controls the kinetics of anion exchange in cesium lead halide nanocrystals.

Anion exchange is a facile, post-synthetic method to tune the emission wavelength of colloidal cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals. While colloidal nanocrystals can exhibit size-dependent phase stability and chemical reactivity, the role of size in the mechanism of anion exchange in CsPbX3 nanocrystals has not been elucidated. We used single-particle fluorescence microscopy to monitor the transformation of individual CsPbBr3 nanocrystals to CsPbI3. By systematically varying the size of the nanocrystals and the concentration of substitutional iodide, we observed that smaller nanocrystals exhibit longer transition times in their fluorescence trajectories, while larger nanocrystals undergo a more abrupt transition during anion exchange. Monte Carlo simulations were used to rationalize the size-dependent reactivity, in which we varied how each exchange event affects the probability for further exchange. Greater cooperativity for simulated ion exchange leads to shorter transition times to complete the exchange. We propose that size-dependent miscibility between CsPbBr3 and CsPbI3 at the nanoscale controls the reaction kinetics. Smaller nanocrystals maintain a homogeneous composition during anion exchange. As the nanocrystal size increases, variations in the octahedral tilting patterns of the perovskite crystals lead to different structures for CsPbBr3 and CsPbI3. Thus, an iodide-rich region must first nucleate within larger CsPbBr3 nanocrystals, which is followed by rapid transformation to CsPbI3. While higher concentrations of substitutional anions can suppress this size-dependent reactivity, the inherent differences in reactivity between nanocrystals of different sizes are important to consider when scaling up this reaction for applications in solid-state lighting and biological imaging.

Experimental Revelation of Surface and Bulk Lattices in Faceted Cu2 O Crystals.

Semiconductor crystals have generally shown facet-dependent electrical, photocatalytic, and optical properties. These phenomena have been proposed to result from the presence of a surface layer with bond-level deviations. To provide experimental evidence of this structural feature, synchrotron X-ray sources areused to obtain X-ray diffraction (XRD) patterns of polyhedral cuprous oxide crystals. Cu2 O rhombic dodecahedra display two distinct cell constants from peak splitting. Peak disappearance during slow Cu2 O reduction to Cu with ammonia borane differentiates bulk and surface layer lattices. Cubes and octahedra also show two peak components, while diffraction peaks of cuboctahedra are comprised of three components. Temperature-varying lattice changes in the bulk and surface regions also show shape dependence. From transmission electron microscopy (TEM) images, slight plane spacing deviations in surface and inner crystal regions are measured. Image processing provides visualization of the surface layer with depths of about 1.5-4nm giving dashed lattice points instead of dots from atomic position deviations. Close TEM examination reveals considerable variation in lattice spot size and shape for different particle morphologies, explaining why facet-dependent properties are emerged. Raman spectrum reflects the large bulk and surface lattice difference in rhombic dodecahedra. Surface lattice difference can change the particle bandgap.

Investigating the crystallization history of Apollo 15 mare basalts using quantitative textural analysis

AbstractMare basalts collected at the Apollo 15 landing site are classified as belonging to either the quartz‐normative suite or the olivine‐normative suite, based on differences in whole‐rock major element chemistry. A wide range of textures are displayed within samples from both suites, which provide insight into eruption processes on the Moon. Here we use crystal size distribution (CSD) analysis and spatial distribution pattern (SDP) analysis of pyroxene, olivine, and plagioclase crystals in eight Apollo 15 mare basalt samples to investigate the crystallization and emplacement of the quartz‐normative and olivine‐normative suites. In general, our results show similarities between the CSDs and SDPs for both mare basalt suites. However, we also report two distinct groups of pyroxene CSD trends that likely represent samples with common cooling histories, originating from comparable depths within respective olivine‐normative and quartz‐normative lava flows. We use our results to determine the relative depths of samples within the lava flows at the Apollo 15 landing site.