Thermal Stability of High-Entropy Alloy Nanoparticles Evaluated by In Situ TEM Observations.

High-entropy alloy (HEA) nanoparticles (NPs) have attracted attention in several fields because of their fascinating properties. The high mechanical strength, good thermal stability, and superior corrosion resistance of HEAs, which are derived from their high configurational entropy, are attractive features. Herein, we investigated the thermal stability of FeCoNiCuPd HEA NPs on reduced graphene oxide via in situ transmission electron microscopy observations at elevated temperatures. The HEA NPs maintained their structure, size, and composition at 700 °C, and their size gradually decreased accompanied by the preferential sublimation of Cu. On the contrary, the deterioration of the monometallic Pd NPs begins at temperatures greater than 700 °C according to Ostwald ripening, which involves the migration of adatoms or mobile molecular species. Theoretical calculations revealed that the detachment of adatoms from clusters (i.e., the first step of Ostwald ripening) was suppressed in the case of HEA NPs because of the high-configuration-entropy effect.

Large phonon drag thermopower boosted by massive electrons and phonon leaking in LaAlO3/LaNiO3/LaAlO3 heterostructure.

An unusually large thermopower (S) enhancement is induced by heterostructuring thin films of the strongly correlated electron oxide LaNiO3. The phonon-drag effect, which is not observed in bulk LaNiO3, enhances S for thin films compressively strained by LaAlO3 substrates. By a reduction in the layer thickness down to three unit cells and subsequent LaAlO3 surface termination, a 10 times S enhancement over the bulk value is observed due to large phonon drag S (Sg), and the Sg contribution to the total S occurs over a much wider temperature range up to 220 K. The Sg enhancement originates from the coupling of lattice vibration to the d electrons with large effective mass in the compressively strained ultrathin LaNiO3, and the electron-phonon interaction is largely enhanced by the phonon leakage from the LaAlO3 substrate and the capping layer. The transition-metal oxide heterostructures emerge as a new playground to manipulate electronic and phononic properties in the quest for high-performance thermoelectrics.

Synthesis of Monodispersedly Sized ZnO Nanowires from Randomly Sized Seeds.

We demonstrate the facile, rational synthesis of monodispersedly sized zinc oxide (ZnO) nanowires from randomly sized seeds by hydrothermal growth. Uniformly shaped nanowire tips constructed in ammonia-dominated alkaline conditions serve as a foundation for the subsequent formation of the monodisperse nanowires. By precisely controlling the sharp tip formation and the nucleation, our method substantially narrows the distribution of ZnO nanowire diameters from σ = 13.5 nm down to σ = 1.3 nm and controls their diameter by a completely bottom-up method, even initiating from randomly sized seeds. The proposed concept of sharp tip based monodisperse nanowires growth can be applied to the growth of diverse metal oxide nanowires and thus paves the way for bottom-up grown metal oxide nanowires-integrated nanodevices with a reliable performance.

Rational Method of Monitoring Molecular Transformations on Metal-Oxide Nanowire Surfaces.

Metal-oxide nanowires have demonstrated excellent capability in the electrical detection of various molecules based on their material robustness in liquid and air environments. Although the surface structure of the nanowires essentially determines their interaction with adsorbed molecules, understanding the correlation between an oxide nanowire surface and an adsorbed molecule is still a major challenge. Herein, we propose a rational methodology to obtain this information for low-density molecules adsorbed on metal oxide nanowire surfaces by employing infrared p-polarized multiple-angle incidence resolution spectroscopy and temperature-programmed desorption/gas chromatography-mass spectrometry. As a model system, we studied the surface chemical transformation of an aldehyde (nonanal, a cancer biomarker in breath) on single-crystalline ZnO nanowires. We found that a slight surface reconstruction, induced by the thermal pretreatment, determines the surface chemical reactivity of nonanal. The present results show that the observed surface reaction trend can be interpreted in terms of the density of Zn ions exposed on the nanowire surface and of their corresponding spatial arrangement on the surface, which promotes the reaction between neighboring adsorbed molecules. The proposed methodology will support a better understanding of complex molecular transformations on various nanostructured metal-oxide surfaces.

Impact of the Spatial Organization of Bifunctional Metal-Zeolite Catalysts on the Hydroisomerization of Light Alkanes.

Improving product selectivity by controlling the spatial organization of functional sites at the nanoscale is a critical challenge in bifunctional catalysis. We present a series of composite bifunctional catalysts consisting of one-dimensional zeolites (ZSM-22 and mordenite) and a γ-alumina binder, with platinum particles controllably deposited either on the alumina binder or inside the zeolite crystals. The hydroisomerization of n-heptane demonstrates that the catalysts with platinum particles on the binder, which separates platinum and acid sites at the nanoscale, leads to a higher yield of desired isomers than catalysts with platinum particles inside the zeolite crystals. Platinum particles within the zeolite crystals impose pronounced diffusion limitations on reaction intermediates, which leads to secondary cracking reactions, especially for catalysts with narrow micropores or large zeolite crystals. These findings extend the understanding of the "intimacy criterion" for the rational design of bifunctional catalysts for the conversion of low-molecular-weight reactants.

Visualizing Progressive Atomic Change in the Metal Surface Structure Made by Ultrafast Electronic Interactions in an Ambient Environment.

Understanding the atomic and molecular phenomena occurring in working catalysts and nanodevices requires the elucidation of atomic migration originating from electronic excitations. The progressive atomic dynamics on metal surface under controlled electronic stimulus in real time, space, and gas environments are visualized for the first time. By in situ environmental transmission electron microscopy, the gas molecules introduced into the biased metal nanogap could be activated by electron tunneling and caused the unpredicted atomic dynamics. The typically inactive gold was oxidized locally on the positive tip and field-evaporated to the negative tip, resulting in the atomic reconstruction on the negative tip surface. This finding of a tunneling-electron-attached-gas process will bring new insights into the design of nanostructures such as nanoparticle catalysts and quantum nanodots and will stimulate syntheses of novel nanomaterials not seen in the ambient environment.

Electron beam induced etching of carbon nanotubes enhanced by secondary electrons in oxygen.

Multi-walled carbon nanotubes (CNTs) are subjected to electron-beam-induced etching (EBIE) in oxygen. The EBIE process is observed in situ by environmental transmission electron microscopy. The partial pressure of oxygen (10 and 100 Pa), energy of the primary electrons (80 and 200 keV), and environment of the CNTs (suspended or supported on a silicon nitride membrane) are investigated as factors affecting the etching rate. The EBIE rate of CNTs was markedly promoted by the effects of secondary electrons that were emitted from a silicon nitride membrane under irradiation by primary electrons. Membrane supported CNTs can be cut by EBIE with a spatial accuracy better than 3 nm, and a nanogap of 2 nm can be successfully achieved between the ends of two suspended CNTs.

Rational Concept for Reducing Growth Temperature in Vapor-Liquid-Solid Process of Metal Oxide Nanowires.

Vapor-liquid-solid (VLS) growth process of single crystalline metal oxide nanowires has proven the excellent ability to tailor the nanostructures. However, the VLS process of metal oxides in general requires relatively high growth temperatures, which essentially limits the application range. Here we propose a rational concept to reduce the growth temperature in VLS growth process of various metal oxide nanowires. Molecular dynamics (MD) simulation theoretically predicts that it is possible to reduce the growth temperature in VLS process of metal oxide nanowires by precisely controlling the vapor flux. This concept is based on the temperature dependent "material flux window" that the appropriate vapor flux for VLS process of nanowire growth decreases with decreasing the growth temperature. Experimentally, we found the applicability of this concept for reducing the growth temperature of VLS processes for various metal oxides including MgO, SnO2, and ZnO. In addition, we show the successful applications of this concept to VLS nanowire growths of metal oxides onto tin-doped indium oxide (ITO) glass and polyimide (PI) substrates, which require relatively low growth temperatures.

Oral hyaluronan relieves knee pain: a review.

Hyaluronan (HA) is a component that is particularly abundant in the synovial fluid. Randomized, double-blinded, placebo-controlled trials carried out between 2008 and 2015 have proven the effectiveness of HA for the treatment of symptoms associated with synovitis, and particularly, knee pain, relief of synovial effusion or inflammation, and improvement of muscular knee strength. The mechanism by which HA exerts its effects in the living body, specifically receptor binding in the intestinal epithelia, has gradually been clarified. This review examines the effects of HA upon knee pain as assessed in clinical trials, as well as the mechanism of these effects and the safety of HA.

Rational Concept for Designing Vapor-Liquid-Solid Growth of Single Crystalline Metal Oxide Nanowires.

Metal oxide nanowires hold great promise for various device applications due to their unique and robust physical properties in air and/or water and also due to their abundance on Earth. Vapor-liquid-solid (VLS) growth of metal oxide nanowires offers the high controllability of their diameters and spatial positions. In addition, VLS growth has applicability to axial and/or radial heterostructures, which are not attainable by other nanowire growth methods. However, material species available for the VLS growth of metal oxide nanowires are substantially limited even though the variety of material species, which has fascinating physical properties, is the most interesting feature of metal oxides. Here we demonstrate a rational design for the VLS growth of various metal oxide nanowires, based on the "material flux window". This material flux window describes the concept of VLS nanowire growth within a limited material flux range, where nucleation preferentially occurs only at a liquid-solid interface. Although the material flux was previously thought to affect primarily the growth rate, we experimentally and theoretically demonstrate that the material flux is the important experimental variable for the VLS growth of metal oxide nanowires. On the basis of the material flux window concept, we discover novel metal oxide nanowires, composed of MnO, CaO, Sm2O3, NiO, and Eu2O3, which were previously impossible to form via the VLS route. The newly grown NiO nanowires exhibited stable memristive properties superior to conventional polycrystalline devices due to the single crystallinity. Thus, this VLS design route offers a useful guideline for the discovery of single crystalline nanowires that are composed of functional metal oxide materials.

Ingestion of hyaluronans (molecular weights 800 k and 300 k) improves dry skin conditions: a randomized, double blind, controlled study.

Hyaluronan (HA) has been increasingly used as a dietary supplement to improve the skin. However, the effect of ingested HA may depend on its molecular weight (MW) because its physiological activities in the body vary with its MW. In this study, we examined the effects of ingested HA with varying MW on the skin. In this randomized, double blind, placebo controlled study, 61 subjects with dry skin received oral HA (120 mg/day), of MWs 800 k and 300 k or placebo, for 6 weeks. The skin moisture contents of the first two groups increased more than those of the placebo group during the ingestion period. In addition, group HA 300 k exhibited significant improvements in skin moisture content 2 weeks after ingestion ended compared with the placebo group. A questionnaire survey about subjective facial aging symptoms showed that the HA treated groups exhibited significantly improved the skin condition compared with the placebo treated group. Furthermore, dermatologists objectively evaluated the clinical symptoms of the facial and whole body skin, showing that no adverse events were related to daily ingestion of HA. This study shows that both of ingesting HAs (MWs 800 k and 300 k) improved the skin condition by increasing the moisture content.

Ingested hyaluronan moisturizes dry skin.

Hyaluronan (HA) is present in many tissues of the body and is essential to maintain moistness in the skin tissues, which contain approximately half the body's HA mass. Due to its viscosity and moisturizing effect, HA is widely distributed as a medicine, cosmetic, food, and, recently marketed in Japan as a popular dietary supplement to promote skin moisture. In a randomized, double-blind, placebo-controlled clinical study it was found that ingested HA increased skin moisture and improved treatment outcomes for patients with dry skin. HA is also reported to be absorbed by the body distributed, in part, to the skin. Ingested HA contributes to the increased synthesis of HA and promotes cell proliferation in fibroblasts. These effects show that ingestion of HA moisturizes the skin and is expected to improve the quality of life for people who suffer from dry skin. This review examines the moisturizing effects of dry skin by ingested HA and summarizes the series of mechanisms from absorption to pharmacological action.

Dietary hyaluronic acid migrates into the skin of rats.

Hyaluronic acid is a constituent of the skin and helps to maintain hydration. The oral intake of hyaluronic acid increases water in the horny layer as demonstrated by human trials, but in vivo kinetics has not been shown. This study confirmed the absorption, migration, and excretion of (14)C-labeled hyaluronic acid ((14)C-hyaluronic acid). (14)C-hyaluronic acid was orally or intravenously administered to male SD rats aged 7 to 8 weeks. Plasma radioactivity after oral administration showed the highest level 8 hours after administration, and orally administered (14)C-hyaluronic acid was found in the blood. Approximately 90% of (14)C-hyaluronic acid was absorbed from the digestive tract and used as an energy source or a structural constituent of tissues based on tests of the urine, feces, expired air, and cadaver up to 168 hours (one week) after administration. The autoradiographic results suggested that radioactivity was distributed systematically and then reduced over time. The radioactivity was higher in the skin than in the blood at 24 and 96 hours after administration. The results show the possibility that orally administered hyaluronic acid migrated into the skin. No excessive accumulation was observed and more than 90% of the hyaluronic acid was excreted in expired air or urine.

Stepwise displacement of catalytically active gold nanoparticles on cerium oxide.

Aberration-corrected environmental transmission electron microscopy (ETEM) proved that catalytically active gold nanoparticles (AuNPs) move reversibly and stepwise by approximately 0.09 nm on a cerium oxide (CeO2) support surface at room temperature and in a reaction environment. The lateral displacements and rotations occur back and forth between equivalent sites, indicating that AuNPs are loosely bound to oxygen-terminated CeO2 and may migrate on the surface with low activation energy. The AuNPs are likely anchored to oxygen-deficient sites. Observations indicate that the most probable activation sites in gold nanoparticulate catalysts, which are the perimeter interfaces between an AuNP and a support, are not structurally rigid.

Restructuring transition metal oxide nanorods for 100% selectivity in reduction of nitric oxide with carbon monoxide.

Transition metal oxide is one of the main categories of heterogeneous catalysts. They exhibit multiple phases and oxidation states. Typically, they are prepared and/or synthesized in solution or by vapor deposition. Here we report that a controlled reaction, in a gaseous environment, after synthesis can restructure the as-synthesized transition metal oxide nanorods into a new catalytic phase. Co3O4 nanorods with a preferentially exposed (110) surface can be restructured into nonstoichiometric CoO1-x nanorods. Structure and surface chemistry during the process were tracked with ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and environmental transmission electron microscopy (E-TEM). The restructured nanorods are highly active in reducing NO with CO, with 100% selectivity for the formation of N2 in temperatures of 250-520 °C. AP-XPS and E-TEM studies revealed the nonstoichiometric CoO1-x nanorods with a rock-salt structure as the active phase responsible for the 100% selectivity. This study suggests a route to generate new oxide catalysts.

Multicrystalline Informatics Applied to Multicrystalline Silicon for Unraveling the Microscopic Root Cause of Dislocation Generation.

A comprehensive analysis of optical and photoluminescence images obtained from practical multicrystalline silicon wafers is conducted, utilizing various machine learning models for dislocation cluster region extraction, grain segmentation, and crystal orientation prediction. As a result, a realistic 3D model that includes the generation point of dislocation clusters is built. Finite element stress analysis on the 3D model coupled with crystal growth simulation reveals inhomogeneous and complex stress distribution and that dislocation clusters are frequently formed along the slip plane with the highest shear stress among twelve equivalents, concentrated along bending grain boundaries (GBs). Multiscale analysis of the extracted GBs near the generation point of dislocation clusters combined with ab initio calculations has shown that the dislocation generation due to the concentration of shear stress is caused by the nanofacet formation associated with GB bending. This mechanism cannot be captured by the Haasen-Alexander-Sumino model. Thus, this research method reveals the existence of a dislocation generation mechanism unique to the multicrystalline structure. Multicrystalline informatics linking experimental, theoretical, computational, and data science on multicrystalline materials at multiple scales is expected to contribute to the advancement of materials science by unraveling complex phenomena in various multicrystalline materials.

Impact of preferential indium nucleation on electrical conductivity of vapor-liquid-solid grown indium-tin oxide nanowires.

Highly conductive and transparent indium-tin oxide (ITO) single-crystalline nanowires, formed by the vapor-liquid-solid (VLS) method, hold great promise for various nanoscale device applications. However, increasing an electrical conductivity of VLS grown ITO nanowires is still a challenging issue due to the intrinsic difficulty in controlling complex material transports of the VLS process. Here, we demonstrate a crucial role of preferential indium nucleation on the electrical conductivity of VLS grown ITO nanowires using gold catalysts. In spite of the fact that the vapor pressure of tin is lower than that of indium, we found that the indium concentration within the nanowires was always higher than the nominal composition. The VLS growth of ITO through gold catalysts significantly differs from ITO film formations due to the emergence of preferential indium nucleation only at a liquid-solid interface. Furthermore, we demonstrate that the averaged resistivity of ITO nanowires can be decreased down to 2.1 × 10(-4) Ω cm, which is the lowest compared with values previously reported, via intentionally increasing the tin concentration within the nanowires.

WGS catalysis and in situ studies of CoO(1-x), PtCo(n)/Co3O4, and Pt(m)Co(m')/CoO(1-x) nanorod catalysts.

Water-gas shift (WGS) reactions on Co3O4 nanorods and Co3O4 nanorods anchoring singly dispersed Pt atoms were explored through building correlation of catalytic performance to surface chemistry of catalysts during catalysis using X-ray absorption spectroscopy, ambient pressure X-ray photoelectron spectroscopy (AP-XPS), and environmental TEM. The active phase of pure Co3O4 during WGS is nonstoichiometric cobalt monoxide with about 20% oxygen vacancies, CoO0.80. The apparent activation energy (Ea) in the temperature range of 180-240 °C is 91.0 ± 10.5 kJ mol(-1). Co3O4 nanorods anchoring Pt atoms (Pt/Co3O4) are active for WGS with a low Ea of 50.1 ± 5.0 kJ mol(-1) in the temperature range of 150-200 °C. The active surface of this catalyst is singly dispersed Pt1Co(n) nanoclusters anchored on Co3O4 (Pt1/Co3O4), evidenced by in situ studies of extended X-ray absorption fine structure spectroscopy. In the temperature range of 200-300 °C, catalytic in situ studies suggested the formation of Pt(m)Co(m') nanoclusters along with the reduction of Co3O4 substrate to CoO(1-x). The new catalyst, Pt(m)Co(m')/CoO(1-x) is active for WGS with a very low Ea of 24.8 ± 3.1 kJ mol(-1) in the temperature range of 300-350 °C. The high activity could result from a synergy of Pt(m)Co(m') nanoclusters and surface oxygen vacancies of CoO(1-x).

Synthesis and disordered crystal structure of Al3O3.5C0.5.

The crystal structure of Al3O3.5C0.5 (Z = 3) has been characterized by X-ray powder diffraction (XRPD), transmission electron microscopy, and electron probe microanalysis. The title compound is trigonal with space group R3̅m (centrosymmetric) and hexagonal unit-cell dimensions a = 0.29588(1) nm, c = 2.84080(7) nm, and V = 0.21538(1) nm(3). The initial structural model was determined by the charge-flipping method and subsequently refined by the Rietveld method. The final structural model showed the positional disordering of one of the two types of Al sites. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were Rwp = 4.03%, S (= Rwp/Re) = 1.17, Rp = 3.08%, RB = 0.82%, and RF = 0.72%. The crystal was composed of antiphase domains, suggesting the occurrence of the high-low phase transition during the cooling process. The transition would be accompanied by the loss of unit-lattice translation, and hence the disordered structural model determined by XRPD might be of the average structure of the low-temperature phase.

Sub-nanometric High-Entropy Alloy Cluster: Hydrogen Spillover Driven Synthesis on CeO2 and Structural Reversibility.

High-entropy alloy (HEA) nanoparticles (NPs) have attracted significant attention as promising catalysts owing to the various unique synergistic effects originating from the nanometer-scale, near-equimolar mixing of five or more components to produce single-phase solid solutions. However, the study of sub-nanometer HEA clusters having sizes of less than 1 nm remains incomplete despite the possibility of novel functions related to borderline molecular states with discrete quantum energy levels. The present work demonstrates the synthesis of CeO2 nanorods (CeO2-NRs) on which sub-nanometer CoNiCuZnPd HEA clusters were formed with the aid of a pronounced hydrogen spillover effect on readily reducible CeO2 (110) facets. The CoNiCuZnPd HEA sub-nanoclusters exhibited higher activity during the reduction of NO by H2 even at low temperatures compared with the corresponding monometallic catalysts. These clusters also showed a unique structural reversibility in response to repeated exposure to oxidative/reductive conditions, based on the sacrificial oxidation of the non-noble metals. Both experimental and theoretical analyses established that multielement mixing in quantum-sized regions endowed the HEA clusters with entirely novel catalytic properties.