The atomic con fi gurations of the quasicrystal-forming ternary Zr 70 Cu 29 Pt 1 metallic glass were calculated by the combination of classical molecular dynamics (MD) and ab-initio MD simulations. The binary Zr 70 Cu 30 was prepared by classical MD and then Pt atoms were inserted into the large voids of Zr 70 Cu 30 , followed by relaxation using ab-initio MD. The coordination number of Pt atoms increased due to relaxation and reached a level comparable to that of Cu. The obtained structural model of Zr 70 Cu 29 Pt 1 was analyzed by Voronoi polyhedral analysis modi fi ed especially for shell structures. We then compared Pt-centered polyhedra and Bergman-type atomic clusters formed in quasicrystals. The combined method of classical and ab-initio MD simulations is e ff ective for the construction of the complicated structural models for glassy materials. [doi:10.2320 / matertrans.MT-M2024007]

Rings comprising chemically bonded atoms are essential topological motifs for the structural ordering of network-forming materials. Quantification of such larger motifs beyond short-range pair correlation is essential for understanding the linkages between the orderings and macroscopic behaviors. Here, we propose two quantitative analysis methods based on rings. The first method quantifies rings by two geometric indicators: roundness and roughness. These indicators reveal the linkages between highly symmetric rings and crystal symmetry in silica and that the structure of amorphous silica mainly consists of distorted rings. The second method quantifies a spatial correlation function that describes three-dimensional atomic densities around rings. A comparative analysis among the functions for different degrees of ring symmetries reveals that symmetric rings contribute to the local structural order in amorphous silica. Another analysis of amorphous models with different orderings reveals anisotropy of the local structural ordering around rings; this contributes to building the intermediate-range ordering. Quantification of large topological motifs is important for understanding chemical linkages between structural ordering and macroscopic behaviors. Here, two quantitative analysis methods based on rings are proposed to reveal information on orders and linkages in crystalline and amorphous materials.

To analyze amorphous structure models obtained by a molecular dynamics (or reverse Monte Carlo) simulation, we propose a virtual angstrom-beam electron diffraction analysis. In this analysis, local electron diffraction patterns are calculated for the amorphous models at equal intervals as performed in the experiment, and the local structures that generate paired diffraction spots in the diffraction patterns are further analyzed by combining them with a Fourier transform and a Voronoi polyhedral analysis. For an example of Zr80Pt20, an aggregate of coordination polyhedra is formed which generates similar diffraction patterns from most parts within the aggregate. Furthermore, the coordination polyhedra are connected in certain orientational relationships which could enhance the intensity of the diffraction spots.

A crystallographically heterogeneous interface was fabricated by growing hexagonal graphene (Gr) using chemical vapor deposition (CVD) on a tetragonal FePd epitaxial film grown by magnetron sputtering. FePd was alternately arranged with Fe and Pd in the vertical direction, and the outermost surface atom was identified primarily as Fe rather than Pd. This means that FePd has a high degree of L10-ordering, and the outermost Fe bonds to the carbon of Gr at the interface. When Gr is grown by CVD, the crystal orientation of hexagonal Gr toward tetragonal L10-FePd selects an energetically stable structure based on the van der Waals (vdW) force. The atomic relationship of Gr/L10-FePd, which is an energetically stable interface, was unveiled theoretically and experimentally. The Gr armchair axis was parallel to FePd [100]L10, where Gr was under a small strain by chemical bonding. Focusing on the interatomic distance between the Gr and FePd layers, the distance was theoretically and experimentally determined to be approximately 0.2 nm. This shorter distance (≈0.2 nm) can be explained by the chemisorption-type vdW force of strong orbital hybridization, rather than the longer distance (≈0.38 nm) of the physisorption-type vdW force. Notably, depth-resolved X-ray magnetic circular dichroism analyses revealed that the orbital magnetic moment (Ml) of Fe in FePd emerged at the Gr/FePd interface (@inner FePd: Ml= 0.16 μB→ @Gr/FePd interface: Ml= 0.32 μB). This interfacially enhanced Mlshowed obvious anisotropy in the perpendicular direction, which contributed to interfacial perpendicular magnetic anisotropy (IPMA). Moreover, the interfacially enhanced Mland interfacially enhanced electron density exhibited robustness. It is considered that the shortening of the interatomic distance produces a robust high electron density at the interface, resulting in a chemisorption-type vdW force and orbital hybridization. Eventually, the robust interfacial anisotropic Mlemerged at the crystallographically heterogeneous Gr/L10-FePd interface. From a practical viewpoint, IPMA is useful because it can be incorporated into the large bulk perpendicular magnetic anisotropy (PMA) of L10-FePd. A micromagnetic simulation assuming both PMA and IPMA predicted that perpendicularly magnetized magnetic tunnel junctions (p-MTJs) using Gr/L10-FePd could realize 10-year data retention in a small recording layer with a circular diameter and thickness of 10 and 2 nm, respectively. We unveiled the energetically stable atomic structure in the crystallographically heterogeneous interface, discovered the emergence of the robust IPMA, and predicted that the Gr/L10-FePd p-MTJ is significant for high-density X nm generation magnetic random-access memory (MRAM) applications.

Homology analysis revealed a hidden correlation between the charge-transport properties and the three-dimensional (3D) phase connectivities of metal/oxide nanocomposites. A group of Pt/CeO2 nanostructured composites with different nanotextures ranging from fibrous networks to lamellae were synthesized and identified by electron tomography. The pre-exponential factor of the ionic conductivity of each nanocomposite showed a linear correlation with one of the homological invariants corresponding to the three-dimensional (3D) connectivity of the ion-conductive CeO2 phase, i.e., 3D-beta(0). The other descriptor for ionic transport, namely, the activation energy, could not be rationally attributed to any of the Betti numbers but mainly correlated with the local crystallinity at the Pt/CeO2 interface. These findings are helpful in the design of electrolytes or electrodes with high oxygen ionic conductivities for application in solid-oxide fuel cells. Moreover, the homological approach proposed in this work can be extended to different nanocomposites, opening up an unexplored pathway for the rational design of nanocomposites based on the homological linkages between their 3D nanotextures and their resulting functionalities.

The network topology in disordered materials is an important structural descriptor for understanding the nature of disorder that is usually hidden in pairwise correlations. Here, we compare the covalent network topology of liquid and solidified silicon (Si) with that of silica (SiO2) on the basis of the analyses of the ring size and cavity distributions and tetrahedral order. We discover that the ring size distributions in amorphous (a)-Si are narrower and the cavity volume ratio is smaller than those in a-SiO2, which is a signature of poor amorphous-forming ability in a-Si. Moreover, a significant difference is found between the liquid topology of Si and that of SiO2. These topological features, which are reflected in diffraction patterns, explain why silica is an amorphous former, whereas it is impossible to prepare bulk a-Si. We conclude that the tetrahedral corner-sharing network of AX(2), in which A is a fourfold cation and X is a twofold anion, as indicated by the first sharp diffraction peak, is an important motif for the amorphous-forming ability that can rule out a-Si as an amorphous former. This concept is consistent with the fact that an elemental material cannot form a bulk amorphous phase using melt quenching technique.

All-solid-state batteries using sodium are promising candidates for next-generation rechargeable batteries due to the limited lithium resources. A practical sodium battery requires an electrolyte with high conductivity. Cubic Na3PS4 exhibiting high conductivity of over 10−4 S cm−1 is obtained by crystallizing amorphous Na3PS4 synthesized by ball milling. Amorphous Na3PS4 crystallizes in a cubic structure and then is transformed into a tetragonal phase upon heating. In this study, in situ observation by transmission electron microscopy demonstrates that the crystallite size drastically increases during the transition from the cubic phase to the tetragonal phase. Moreover, an electron diffraction analysis reveals that amorphous domains and nano-sized crystallites coexist in the cubic Na3PS4 specimen, while the tetragonal phase contains micro-sized crystallites. The nano-sized crystallites and the composite formed by crystallites and amorphous domains are most likely responsible for the increase in conductivity in the cubic Na3PS4 specimens.

Developing highly active electrocatalysts with low costs and long durability for oxygen evolution reactions (OERs) is crucial towards the practical implementations of electrocatalytic water-splitting and rechargeable metal-air batteries. Anodized nanostructured 3d transition metals and alloys with the formation of OER-active oxides/hydroxides are known to have high catalytic activity towards OERs but suffer from poor electrical conductivity and electrochemical stability in harsh oxidation environments. Here we report that high OER activity can be achieved from the metallic state of Ni which is passivated by atomically thick graphene in a three-dimensional nanoporous architecture. As a free-standing catalytic anode, the non-oxide transition metal catalyst shows a low OER overpotential, high OER current density and long cycling lifetime in alkaline solutions, benefiting from the high electrical conductivity and low impedance resistance for charge transfer and transport. This study may pave a new way to develop high efficiency transition metal OER catalysts for a wide range of applications in renewable energy.

Vapor phase dealloying (VPD) is an environmentally-friendly method for fabricating nanoporous materials by utilizing the saturated vapor pressure difference of elements to selectively drive sublimation of one or more components from an alloy. VPD kinetics has not been explored and rate-controlling factors of the solid-gas transformation within complex nanostructure remain unknown. Using manganese-zinc alloys as a prototype system, we systematically investigated the dependence of dealloying velocity on temperature and pressure and presented a model to quantitatively describe the dealloying kinetics. We found that the dealloying velocity exhibits a linear to power law transition at a critical dealloying depth, resulting from the interplay between the kinetic process of dealloying and dealloyed microstructure. This transition bridges ballistic evaporation at early time to Knudsen diffusion of Zn vapor in developed pore channels where the Zn partial pressure at the dealloying front reaches the local equilibrium between the solid and vapor phases. By comparing activation energies for VPD and bulk zinc sublimation, the entire energy landscape of VPD is measured. The fundamental understanding of VPD kinetics paves an effective way to design dealloyable precursor alloys and to optimize dealloyed microstructure of VPD materials for a wide range of applications. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The structure analysis of amorphous materials still leaves much room for improvement. Owing to the lack of translational or rotational symmetry of amorphous materials, it is important to develop a different approach from that used for crystals for the structure analysis of amorphous materials. Here, the angstrom-beam electron diffraction method was used to obtain the local structure information of amorphous materials at a sub-nanometre scale. In addition, we discussed the relationship between the global and local diffraction intensities of amorphous structures, and verified the effectiveness of the proposed method through basic diffraction simulations. Finally, some applications of the proposed method to structural and functional amorphous materials are summarized.

Although ionic conductors have been thoroughly investigated, topological features of these materials' nanotextures have been surprisingly overlooked. Here, we report fabrication of a metal-oxide nanocomposite consisting of intertwined phases of platinum (Pt) metal and oxygen-ion conductive cerium oxide (CeO2), i.e., Pt#CeO2. Sectional TEM observations coupled with topological analysis demonstrated that Pt#CeO2 composites having different nanostructures can be classified with a topological measure that corresponds to the phase connectivity of CeO2, namely, the Betti number beta 0, and another that corresponds to holes of the Pt phase, namely, the Betti number beta 1. The samples' oxygen ionic conductivity Pt#CeO2 was measured at elevated temperatures in air by alternating current impedance spectroscopy. It was found that the nanostructure changed from a striped appearance to a maze-like appearance as the value of beta 1 / beta 0 decreased. Both the activation energy E and the pre-exponential factor sigma 0 for the oxygen ionic conductivity were found to be independent of beta 1 and exhibited linear, negative correlations with beta 0. The topological connectivity of the ion-conductive CeO2 phase, which was quantified with the Betti number beta 0, was suitable as a descriptor to correlate the image data of nanostructures with their ionic transport properties.

Characterization of oxide films formed on brightly annealed Al-added 18%Cr steel was performed by glow discharge optical emission spectrometry, transmission electron microscopy, and hard X-ray photoelectron spectroscopy. The experimental data indicated that the oxide films with an average thickness of about 15 nm were mainly composed of amorphous Al2O3 , which was identified from the locations of the first and second rings in the halo pattern obtained by electron diffraction. The data also suggested the presence of Si4+ and Si3+ in the outermost surface layer of the oxide films. The formation of amorphous Al2O3 found in the brightly annealed Al-added 18%Cr steel is discussed on the basis of the present experimental data, with reference to the molecular-dynamics calculation made by Gutierrez and Johansson.

The structural origin of the slow dynamics in glass formation remains to be understood owing to the subtle structural differences between the liquid and glass states. Even from simulations, where the positions of all atoms are deterministic, it is difficult to extract significant structural components for glass formation. In this study, we have extracted significant local atomic structures from a large number of metallic glass models with different cooling rates by utilising a computational persistent homology method combined with linear machine learning techniques. A drastic change in the extended range atomic structure consisting of 3-9 prism-type atomic clusters, rather than a change in individual atomic clusters, was found during the glass formation. The present method would be helpful towards understanding the hierarchical features of the unique static structure of the glass states. In glass formation, the dynamics of extended structures beyond atomic short-range order is yet to be understood. Here, persistent homology, combined with machine learning, reveals superstructures made of 3-to-9 prism-type atomic clusters which undergo drastic changes according to the glass cooling rate.

<jats:title>Abstract</jats:title><jats:p>The broken symmetry in the atomic-scale ordering of glassy versus crystalline solids leads to a daunting challenge to provide suitable metrics for describing the order within disorder, especially on length scales beyond the nearest neighbor that are characterized by rich structural complexity. Here, we address this challenge for silica, a canonical network-forming glass, by using hot versus cold compression to (i) systematically increase the structural ordering after densification and (ii) prepare two glasses with the same high-density but contrasting structures. The structure was measured by high-energy X-ray and neutron diffraction, and atomistic models were generated that reproduce the experimental results. The vibrational and thermodynamic properties of the glasses were probed by using inelastic neutron scattering and calorimetry, respectively. Traditional measures of amorphous structures show relatively subtle changes upon compacting the glass. The method of persistent homology identifies, however, distinct features in the network topology that change as the initially open structure of the glass is collapsed. The results for the same high-density glasses show that the nature of structural disorder does impact the heat capacity and boson peak in the low-frequency dynamical spectra. Densification is discussed in terms of the loss of locally favored tetrahedral structures comprising oxygen-decorated SiSi<jats:sub>4</jats:sub> tetrahedra.</jats:p>

Although previous molecular dynamics studies proposed the existence of Zr-centered Frank-Kasper Z16 structures in Cu-Zr metallic glasses, it cannot be concluded yet, owing to the degeneracy problem of the Voronoi index and the artifact in sets of potentials for Cu-Zr systems. We solve both problems by combining a recently developed Finnis-Sinclair potentials to generate realistic atomic structures and the p 3 code to properly differentiate local structures. In previous studies, the Voronoi index (0, 0, 12, 4) was typically associated with Frank-Kasper Z16 local structures. However, we demonstrate that this index includes two types of polyhedra, only one of which is associated with the Frank-Kasper Z16 structures. We reveal that the Z16 structures are more frequent than the other structures and that the two have different behaviors. The tendency of Zr-centered Z16 local structures to be neighbors of Cu-centered icosahedral local structures is also confirmed. Our findings illustrate the importance of properly differentiating local structures in order to elucidate the behavior of metallic glasses at the atomic scale.

Understanding the formation and evolution of bicontinuous nano-porous structure during dealloying has been one of the most challenging subjects of dealloying research. However, previous in situ investigations either suffer from insufficient spatial resolution (e.g., X-ray tomography) or lack morphology visualization and mass information (e.g., scanning tunneling microscopy). In this work, we report the kinetics of the whole course of dealloying by utilizing liquid-cell aberration-corrected scanning transmission electron microscopy. With Z-contrast imaging analysis, the in situ sub-nanoscale characterization reveals two new phenomena, an initial period of dealloying indicative of an initial length scale for bulk dealloying and a large volume shrinkage in a nanoscale alloy precursor. We explain the particle-size-dependent volume shrinkage with the formation of a dense shell and quantify the dependence with a simple geometric model. These insights into the mechanisms of dealloying will enable deliberate designs of nanoporous structures.

To investigate multi-boson peaks (multi-BP), terahertz time-domain spectroscopy was performed on amorphous silicon monoxide (a-SiO), which exhibits unusual disproportion in the nanoscale region where the SiO2 and Si regions are separated. In the resulting THz spectrum, the BP was observed at 2.4 THz, as a broad asymmetric peak, and the BP frequency was evidently higher than that of silica glass. The results suggest that the higher BP frequency of a-SiO in the infrared spectrum originates from the a-Si cluster region.

The solid electrolyte interphase (SEI) spontaneously formed on anode surfaces as a passivation layer plays a critical role in the lithium dissolution and deposition upon discharge/charge in lithium ion batteries and lithium-metal batteries. The formation kinetics and failure of the SEI films are the key factors determining the safety, power capability, and cycle life of lithium ion and lithium-metal batteries. Since SEI films evolve with the volumetric and interfacial changes of anodes, it is technically challenging in experimental study of SEI kinetics. Here operando observations are reported of SEI formation, growth, and failure at a high current density by utilizing a mass-sensitive Cs-corrected scanning transmission electron microscopy. The sub-nano-scale observations reveal a bilayer hybrid structure of SEI films and demonstrate the radical assisted SEI growth after the SEI thickness beyond the electron tunneling regime. The failure of SEI films is associated with rapid dissolution of inorganic layers when they directly contact with the electrolyte in broken SEI films. The initiation of cracks in SEI films is caused by heterogeneous volume changes of the electrodes during delithiation. These microscopic insights have important implications in understanding SEI kinetics and in developing high-performance anodes with the formation of robust SEI films.

The structure of glassy, liquid, and amorphous materials is still not well understood, due to the insufficient structural information from diffraction data. In this article, attempts are made to understand the origin of diffraction peaks, particularly of the first sharp diffraction peak (FSDP, Q(1)), the principal peak (PP, Q(2)), and the third peak (Q(3)), observed in the measured diffraction patterns of disordered materials whose structure contains tetrahedral motifs. It is confirmed that the FSDP (Q(1)) is not a signature of the formation of a network, because an FSDP is observed in tetrahedral molecular liquids. It is found that the PP (Q(2)) reflects orientational correlations of tetrahedra. Q(3), that can be observed in all disordered materials, even in common liquid metals, stems from simple pair correlations. Moreover, information on the topology of disordered materials was revealed by utilizing persistent homology analyses. The persistence diagram of silica (SiO2) glass suggests that the shape of rings in the glass is similar not only to those in the crystalline phase with comparable density (alpha-cristobalite), but also to rings present in crystalline phases with higher density (alpha-quartz and coesite); this is thought to be the signature of disorder. Furthermore, we have succeeded in revealing the differences, in terms of persistent homology, between tetrahedral networks and tetrahedral molecular liquids, and the difference/similarity between liquid and amorphous (glassy) states. Our series of analyses demonstrated that a combination of diffraction data and persistent homology analyses is a useful tool for allowing us to uncover structural features hidden in halo pattern of disordered materials. (C) 2019 The Ceramic Society of Japan. All rights reserved.

The coarsening of crystalline nanoparticles, driven by reduction of surface energy, is the main factor behind the degeneration of their physical and chemical properties. The kinetic phenomenon has been well described by various models, such as Ostwald ripening and coalescence. However, the coarsening mechanisms of metallic glass nanoparticles (MGNs) remains largely unknown. Here we report atomic-scale observations on the coarsening kinetics of MGNs at high temperatures by in situ heating high-resolution transmission electron microscopy. The coarsening of the amorphous nanoparticles takes place by fast coalescence which is dominated by facet-free surface diffusion at a lower onset temperature. Atomic-scale observations and kinetic Monte Carlo simulations suggest that the high surface mobility and the structural isotropy of MGNs, originating from the disordered structure and unique supercooled liquid state, promote the fast coalescence of the amorphous nanoparticles at relatively lower temperatures.

The crystallographic features of Bi1-xCaxFeO3 samples with x = 0.10, 0.15, 0.20, and 0.30 compositions are investigated by transmission electron microscopy. Perovskite-based modulated structures are found in all the samples except for the x = 0.10 sample where a rhombohedral R3c BiFeO3-type structure is observed at room temperature. The in situ heating experiment indicates that the modulated structure appears even in the x = 0.10 sample at 673K or higher. At room temperature, the modulation direction is found to change at approximately x = 0.20. The models of the modulated structures are constructed by introducing periodic antiphase boundaries in terms of the M-3-type rotational displacements of the FeO6 octahedra. The electron diffraction patterns simulated from the models are in good agreement with the experimental results. The composition dependence of the modulated structures is also discussed.

Since their discovery in 1960(1), metallic glasses based on a wide range of elements have been developed(2). However, the theoretical prediction of glass-forming compositions is challenging and the discovery of alloys with specific properties has so far largely been the result of trial and error(3-8). Bulk metallic glasses can exhibit strength and elasticity surpassing those of conventional structural alloys(9-11), but the mechanical properties of these glasses are critically dependent on the glass transition temperature. At temperatures approaching the glass transition, bulk metallic glasses undergo plastic flow, resulting in a substantial decrease in quasi-static strength. Bulk metallic glasses with glass transition temperatures greater than 1,000 kelvin have been developed, but the supercooled liquid region (between the glass transition and the crystallization temperature) is narrow, resulting in very little thermoplastic formability, which limits their practical applicability. Here we report the design of iridium/nickel/tantalum metallic glasses (and others also containing boron) with a glass transition temperature of up to 1,162 kelvin and a supercooled liquid region of 136 kelvin that is wider than that of most existing metallic glasses(12). Our Ir-Ni-Ta-(B) glasses exhibit high strength at high temperatures compared to existing alloys: 3.7 gigapascals at 1,000 kelvin(9,13). Their glass-forming ability is characterized by a critical casting thickness of three millimetres, suggesting that small-scale components for applications at high temperatures or in harsh environments can readily be obtained by thermoplastic forming(14). To identify alloys of interest, we used a simplified combinatorial approach(6-8) harnessing a previously reported correlation between glass-forming ability and electrical resistivity(15-17). This method is non-destructive, allowing subsequent testing of a range of physical properties on the same library of samples. The practicality of our design and discovery approach, exemplified by the identification of high-strength, high-temperature bulk metallic glasses, bodes well for enabling the discovery of other glassy alloys with exciting properties.

It has been known for decades that nanopores produced by selective leaching during galvanic corrosion can lead to dramatic loss of materials ductility and strength under tension. However, the underlying atomic mechanisms of the nanopore induced embrittlement remain to be poorly known. Here we report in situ observations of the deformation and failure of dealloyed nanoporous gold by utilizing the state-of-the art aberration-corrected transmission electron microscopy and fast direct electron detection camera. Our time-resolved atomic observations reveal that the brittle failure of the nanoporous gold originates from plastic instability of individual gold ligaments by the interplay between dislocation plasticity and stress-driving surface diffusion. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Localized surface plasmon resonance (LSPR) excitation enhanced chemical and electrochemical reactions represent a promising pathway for solar-to-chemical energy conversion. However, plasmonic catalysts usually suffer from low collection efficiency of hot charge carries generated by LSPR excitation due to short lifetime of hot carriers and fast electron-hole recombination. Schottky barriers between plasmonic catalysts and semiconducting supports have been utilized to prevent the electron-hole recombination. However, the interfacial barriers also hinder low-energy hot charge collection and thus affect solar-to-chemical energy conversion efficiency. Here we report that bicontinuous nanoporous gold as a Schottky barriers-free direct plasmonic catalyst can significantly enhance electro-oxidation of alcohol molecules. A high energetic hole yield of 0.486% is achieved, which is 4 times higher than that of discrete plasmonic AuAg nanoparticles. The direct plasmonic catalyst offers the highest methanol oxidation current density of 531 mu A cm(-2) among all known Au catalysts. This work provides compelling evidence that higher hot carrier collection efficiency can be achieved from direct plasmonic electrocatalysis without the assistance of Schottky junctions and has important implications in developing high efficiency plasmonic catalysts for photo-enhanced electrochemical reactions.

The real capacity of graphene and the lithium-storage process in graphite are two currently perplexing problems in the field of lithium ion batteries. Here we demonstrate a three-dimensional bilayer graphene foam with few defects and a predominant Bernal stacking configuration, and systematically investigate its lithium-storage capacity, process, kinetics, and resistances. We clarify that lithium atoms can be stored only in the graphene interlayer and propose the first ever planar lithium-intercalation model for graphenic carbons. Corroborated by theoretical calculations, various physiochemical characterizations of the staged lithium bilayer graphene products further reveal the regular lithium-intercalation phenomena and thus fully illustrate this elementary lithium storage pattern of two-dimension. These findings not only make the commercial graphite the first electrode with clear lithium-storage process, but also guide the development of graphene materials in lithium ion batteries.

An aprotic lithium-oxygen battery with an ultrahigh theoretical energy density has attracted significant attention as the next-generation electrochemical energy device demanded by all-electric vehicles and other high-energy devices. Extensive effort has recently been devoted to improving the performances of cathodes, anodes, and electrolytes. However, as an integrated system, the overall battery properties are not determined by the individual components but by the synergy of all components. Despite important progress in the development of cathodes, anodes, and electrolytes, the system-level design and assembly of lithium-oxygen batteries have not benefited from these recent advances. Here, we report a graphene-based quasi-solid-state lithium-oxygen battery consisting of a rationally designed 3D porous graphene cathode, redox mediator-modified gel polymer electrolyte, and porous graphene/Li anode. This integrated prototype battery simultaneously addresses the major challenges of lithium-oxygen batteries and achieves stable cycling at a large capacity, low charge overpotential and high rate in both coin-type and large-scale pouch-type batteries. For the first time, these lithium-oxygen batteries as a whole device deliver gravimetric and volumetric energy densities higher than those of a commercial Li-ion polymer battery. This study represents important progress toward the practical implementation of full-performance lithium-oxygen batteries.

The deformation microstructure of an interdendritie 18 R long-period stacking ordered (LPSO) phase in an Mg-Zn-Y. alloy subjected to shock loading was investigated by transmission electron microscopy. It was found that kink banding, the key deformation mode of LPSO phases under quasi-static loading, is suppressed by shock loading. Instead, second-order pyramidal slip by < c + a > dislocations, which has not been observed in LPSO before, contributes to the plastic deformation of LPSO, in addition to the < a > dislocations. The rate-dependent deformation modes of LPSO have an important implication in understanding the mechanical behaviour of LPSO strengthened Mg alloys under extreme loading conditions.

Pristine thin films of amorphous Ge prepared by sputtering are unstable and form coarse crystalline particles of 100nm in size upon crystallization by electron irradiation. These crystalline particles exhibit unusual diffraction patterns that cannot be understood from the diamond cubic structure. The structure has previously been assumed to be a metastable hexagonal form. In the present work, the structure of the coarse crystalline particles has been analysed in detail by transmission electron microscopy, considering the possibility that those diffraction patterns might occur with the diamond cubic structure if the particle consists of thin twin layers. By high-resolution lattice imaging the particles have been shown to be of the diamond cubic structure containing a high density of twins and stacking faults parallel to {111}. With such defects, diffraction patterns can be complex because of the following effects: superposition of two or more diffraction patterns of the same structure but of different orientations, double diffraction through twin crystals, and streaks parallel to the thin crystal which give rise to extra diffraction spots. It is found that diffraction patterns taken from various orientations can be explained in terms of these effects.

Heavy chemical doping and high electrical conductivity are two key factors for metal-free graphene electrocatalysts to realize superior catalytic performance toward hydrogen evolution. However, heavy chemical doping usually leads to the reduction of electrical conductivity because the catalytically active dopants give rise to additional electron scattering and hence increased electrical resistance. A hierarchical nanoporous graphene, which is comprised of heavily chemical doped domains and a highly conductive pure graphene substrate, is reported. The hierarchical nanoporous graphene can host a remarkably high concentration of N and S dopants up to 9.0 at% without sacrificing the excellent electrical conductivity of graphene. The combination of heavy chemical doping and high conductivity results in high catalytic activity toward electrochemical hydrogen production. This study has an important implication in developing multi-functional electrocatalysts by 3D nanoarchitecture design.

The mechanical properties of crystalline materials can be quantitatively described by crystal defects of solute atoms, dislocations, twins, and grain boundaries with the models of solid solution strengthening, Taylor strain hardening and Hall-Petch grain boundary strengthening. However, for metallic glasses, a well-defined structure feature which dominates the mechanical properties of the disordered materials is still missing. Here, we report that nanoscale spatial heterogeneity is the inherent structural feature of metallic glasses. It has an intrinsic correlation with the strength and deformation behavior. The strength and Young's modulus of metallic glasses can be defined by the function of the square root reciprocal of the characteristic length of the spatial heterogeneity. Moreover, the stretching exponent of time-dependent strain relaxation can be quantitatively described by the characteristic length. Our study provides compelling evidence that the spatial heterogeneity is a feasible structural indicator for portraying mechanical properties of metallic glasses.

In comparison to conventional supercapacitors that commonly fall short of energy densities, the intercalation pseudocapacitors have combined high charge-storage capacity and fast charge/discharge rates from their unique charge storage mechanism of fast kinetics without the limitation of diffusion. Nevertheless, only very limited crystalline materials have a structure that can fulfill the strict demands of fast ion transport pathways and insignificant structural variation upon ion insertion and extraction for the intercalation pseudocapacitance. Here we report that amorphous titanium dioxide, grown on highly conductive nanoporous graphene frameworks by atomic layer deposition, is capable of storing and delivering a large capacity at high rates by pseudocapacitive and bulk-form Li+ intercalation/de-intercalation reactions. Different from intercalation pseudocapacitive crystals, amorphous TiO2 experiences local structure changes during Li+ insertion and extraction which essentially only lead to insignificant constraints on the overall kinetics as a result of loose packing and structure disorder of amorphous materials. This study paves a new way to develop high-energy capacitive materials in a wide spectrum of amorphous materials and may promote the practical implementation of high-rate and large-capacity energy storage.

RuO2 displays excellent bifunctional catalysis towards the oxygen reduction and evolution reactions of Li-O-2 battery. Nevertheless, how the solid catalyst successively catalyzes solid Li2O2 formation and decomposition, confronting passivation and loss of RuO2/Li2O2 contact, during discharging and charging remains a mystery. Here we report operando observations of RuO2 catalyzed oxygen reduction and evolution reactions of Li2O2 by utilizing a liquid cell scanning transmission electron microscope. Upon discharging, RuO2 obviously accelerates formation of soluble LiO2 intermediates and acts as preferential sites of Li2O2 precipitation. During charging, the catalytic activation of RuO2 takes place at electrolyte-RuO2-Li2O2 triple-phase interfaces. Importantly, RuO2 not only catalyzes the decomposition of directly contacted Li2O2, but also promotes oxidation of soluble LiO2 for rapid dissolution of isolated Li2O2 nanoparticles by a chemical comproportionation reaction. The observation unveils how RuO2 catalyzes the formation and decomposition of Li2O2 during discharging and charging and provides nanoscale insights into cathodic reactions of Li-O-2 batteries with solid catalysts.

Developing advanced lithium-ion batteries that afford both high energy density and high power density has been one of the crucial research targets in the field of electrochemical energy storage. Realization of fast Li+ storage would require a smart electrode design that enables simultaneous enhancements in ion and electron transports as well as a fast and facile bulk-form solid-state reaction. Here we report a high-performance 3D bilayered composite electrode constructed by bicontinuous nanoporous graphene and thin molybdenum oxide stacking films. The novel electrode offers fast kinetics of Li+ diffusion and reactions and, consequently, delivers a large specific capacity of 710 mAh g(-1), the excellent rate performance of charging within seconds and an ultra-long lifetime over 13,000 discharge-charge cycles. High and stable volumetric capacities up to 900 mAh cm(-3) have also been achieved with the squeezed composite electrodes. This study shines light into the realization of a high-performance graphene-based porous electrode for advanced lithium-ion batteries and will inspire the development of new 3D hybrid materials for high-rate and large-capacity electrochemical energy storage.

Rechargeable non-aqueous lithium-oxygen batteries with a large theoretical capacity are emerging as a high-energy electrochemical device for sustainable energy strategy. Despite many efforts made to understand the fundamental Li-O-2 electrochemistry, the kinetic process of cathodic reactions, associated with the formation and decomposition of a solid Li2O2 phase during charging and discharging, remains debate. Here we report direct visualization of the charge/discharge reactions on a gold cathode in a non-aqueous lithium-oxygen micro-battery using liquid-cell aberration-corrected scanning transmission electron microscopy (STEM) combining with synchronized electrochemical measurements. The real-time and real-space characterization by time-resolved STEM reveals the electrochemical correspondence of discharge/charge overpotentials to the nucleation, growth and decomposition of Li2O2 at a constant current density. The nano-scale operando observations would enrich our knowledge on the underlying reaction mechanisms of lithium-oxygen batteries during round-trip discharging and charging and shed lights on the strategies in improving the performances of lithium-oxygen batteries by tailoring the cathodic reactions.

1T-1H metal-semiconductor interfaces in two-dimensional (2D) transition-metal dichalcogenides (TMDs) play a crucial role in utilizing the band gaps of TMDs for applications in electronic devices. Although the 1T-1H two-phase structure has been observed in exfoliated 2D nanosheets and chemically or physically treated TMDs, it cannot in principle be achieved in large-scale TMD monolayers grown by chemical vapor deposition (CVD), which is a fabrication method for electronic device applications, because of the metastable nature of the 1T phase. In this study we report CVD growth of 1T-1H two phase TMD monolayers by controlling thermal strains and alloy compositions. It was found that in-plane thermal strains arising from the difference in thermal expansion coefficients between TMD monolayers and substrates can drive the 1H to 1T transition during cooling after CVD growth. Moreover, grain boundaries in the 2D crystals act as the nucleation sites of the 1T phase and the lattice strain perturbations from alloying noticeably promote the formation of the metastable 1T phase. This work has an important implication in tailoring structure and properties of CVD grown 2D TMDs by phase engineering.

Three-dimensional bicontinuous open (3DBO) nanoporosity has been recognized as an important nanoarchitecture for catalysis, sensing, and energy storage. Dealloying, i.e., selectively removing a component from an alloy, is an efficient way to fabricate nanoporous materials. However, current electrochemical and liquid-metal dealloying methods can only be applied to a limited number of alloys and usually require an etching process with chemical waste. Here, we report a green and universal approach, vapor-phase dealloying, to fabricate nanoporous materials by utilizing the vapor pressure difference between constituent elements in an alloy to selectively remove a component with a high partial vapor pressure for 3DBO nanoporosity. We demonstrate that extensive elements, regardless of chemical activity, can be fabricated as nanoporous materials with tunable pore sizes. Importantly, the evaporated components can be fully recovered. This environmentally friendly dealloying method paves a way to fabricate 3DBO nanoporous materials for a wide range of structural and functional applications.

We have examined the local atomic configurations of amorphous Fe-Si-B alloys by means of electron diffraction pair-distribution-function analysis and compared them with those of a metastable sigma phase formed during the crystallization process. We found a great structural similarity, not only at short range but also at medium range up to 1.0 nm, between amorphous Fe-Si-B and sigma phase structures. The results imply that the sigma phase structure can be regarded as a good crystalline approximant for the glass structures in this alloy system. The connections of coordination polyhedra in the sigma phase structure were also discussed.

A series of boron-rich boron carbides are investigated to explore the effect of boron/carbon ratios on the microstructure and mechanical properties of the complex material. It has been found that excess boron substitution gives rise to expanded lattice constants, orientational asymmetry of the chain structure and distortion of the icosahedra of rhombohedra B4C units in comparison with conventional carbon rich boron carbides. Microstructure characterization reveals a high density of stacking faults and growth twins in boron-rich boron carbides. Nanoindentation measurements demonstrate that the hardness and modulus of boron-rich boron carbides decrease with the increase of boron content while the B10.2C sample with the highest boron substitution shows relatively high hardness and modulus. This study suggests that the structure of single-phase covalent materials could be tailored by self-alloying for improved mechanical properties. (C) 2017 Elsevier Ltd. All rights reserved.

Although nanoscale spatial heterogeneity of metallic glasses has been demonstrated by extensive experimental and theoretical investigations, the nature of spatial heterogeneity remains poorly known owing to the absence of a structural depiction of the inhomogeneity from experimental insight. Here we report the experimental characterization of the spatial heterogeneity of a metallic glass by utilizing state-of-the-art angstrom-beam electron diffraction and scanning transmission electron microscopy. The subnanoscale electron diffraction reveals that the nanoscale spatial heterogeneity and corresponding density fluctuation have a close correlation with the local structure variation from icosahedronlike to tetragonal crystal-like order. The structural insights of spatial heterogeneity have important implications in understanding the properties and dynamics of metallic glasses.

3D dealloyed nanoporous metals have emerged as a new class of catalysts for various chemical and electrochemical reactions. Similar to other heterogeneous catalysts, the surface atomic structure of the nanoporous metal catalysts plays a crucial role in catalytic activity and selectivity. Through surfactant-assisted bottom-up synthesis, the surface-structure modification has been successfully realized in low-dimensional particulate catalysts. However, the surface modification by top-down dealloying has not been well explored for nanoporous metal catalysts. Here, a surfactant-free approach to tailor the surface structure of nanoporous gold by surface relaxation via electrochemical redox cycling is reported. By controlling the scan rates, nanoporous gold with abundant {111} facets or {100} facets can be designed and fabricated with dramatically improved electrocatalysis toward the ethanol oxidation reaction.

Operando scanning transmission electron microscopy observations of cathodic reactions in a liquid-cell Li-O-2 microbattery in the presence of the redox mediator tetrathiafulvalene (TTF) in 1.0 m LiClO4 dissolved dimethyl sulfoxide electrolyte are reported. It is found that the TTF addition does not obviously affect the discharge reaction for the formation of a solid Li2O2 phase. The coarsening of Li2O2 nanoparticles occurs via both conventional Ostwald ripening and nonclassical crystallization by particle attachment. During charging, the oxidation reaction at significantly reduced charge potentials mainly takes place at Li2O2/electrolyte interfaces and has obvious correspondence with the oxidized TTF+ distributions in the electric fields of the charged electrode. This study provides direct evidence that TTF truly plays a role in promoting the decomposition of Li2O2 as a soluble charge-transfer agent between the electrode and the Li2O2.

Tuning surface structures by bottom-up synthesis has been demonstrated as an effective strategy to improve the catalytic performances of nanoparticle catalysts. Nevertheless, the surface modification of three-dimensional nanoporous metals, fabricated by a top-down dealloying approach, has not been achieved despite great efforts devoted to improving the catalytic performance of three-dimensional nanoporous catalysts. Here we report a surfactant-modified dealloying method to tailor the surface structure of nanoporous gold for amplified electrocatalysis toward methanol oxidation and oxygen reduction reactions. With the assistance of surfactants, {111} or {100} faceted internal surfaces of nanoporous gold can be realized in a controllable manner by optimizing dealloying conditions. The surface modified nanoporous gold exhibits significantly enhanced electrocatalytic activities in comparison with conventional nanoporous gold. This study paves the way to develop high-performance three-dimensional nanoporous catalysts with a tunable surface structure by top-down dealloying for efficient chemical and electrochemical reactions.

One central material issue in spintronics is the search for high temperature (above room temperature) magnetic semiconductors. We report on the formation of a transparent magnetic semiconductor with embedded ferromagnetic metallic glass nano-granules, showing a Curie temperature of similar to 600 K. Soft X-ray magnetic circular dichroism data verify its intrinsic room-temperature ferromagnetism. Owing to the unique structure of ferromagnetic nano-granules embedded in the hostmagnetic semiconductor, additional interfacial exchange anisotropy emerges and stabilizes the ferromagnetism. The magnetotransport measurements of the amorphous nanocomposite indicate that its anomalous Hall effect is dominated by the extrinsic mechanism of the side-jump due to the spin-dependent impurity. (C) 2017 Elsevier Ltd. All rights reserved.

Two-dimensional (2D) materials are promising for applications in a wide range of fields because of their unique properties. Hydrogen boride sheets, a new 2D material recently predicted from theory; exhibit intriguing electronic and mechanical properties as well as hydrogen storage capacity. Here, we report the experimental realization of 2D hydrogen boride sheets with an empirical formula of H1B1, produced by exfoliation and complete ion-exchange between protons and magnesium cations in magnesium diboride (MgB2) with an average yield of 42.3% at room temperature. The sheets feature an sp(2)-bonded boron planar structure without any long-range order. A hexagonal boron network with bridge hydrogens is suggested as the possible local structure, where the absence of lon-grange order was ascribed to the presence of three different anisotropic domains originating from the 2-fold symmetry of the hydrogen positions against the 6-fold symmetry of the boron networks, based on X-ray diffraction, X-ray atomic pair distribution functions, electron diffraction, transmission electron microscopy, photo absorption, core-level binding energy data, infrared absorption, electron energy loss spectroscopy, and density functional theory calculations. The established cation-exchange method for metal diboride opens new avenues for the mass production of several types of boron-based 2D materials by countercation selection and functionalintion.

Grain boundaries (GBs) are unavoidable crystal defects in polycrystalline materials and significantly influence their properties. However, the structure and chemistry of GBs in 2D transition metal dichalcogenide alloys have not been well established. Here we report significant chemical selectivity of transition metal atoms at GB dislocation cores in Mo1-xWxS2 monolayers. Different from classical elastic field driven dislocation segregation in bulk crystals, the chemical selectivity in the 2D crystals originates prominently from variation of atomic coordination numbers at dislocation cores. This observation provides atomic insights into the topological effect on the chemistry of crystal defects in 2D materials.

Realizing a large specific area in disordered metallic glasses is of great scientific and technological importance. Here we report a nanoporous multicomponent metallic glass fabricated by the combination of selective phase dissolution and passivation of a spinodally decomposed glassy precursor. The nanoporous metallic glass shows superior hydrogen uptake performance by taking advantage of the large specific surface area of the nanoporous structure and the high diffusivity of hydrogen in metallic glasses. The facile route of selective corrosion and passivation, decoupling the galvanic corrosion and alloy stability, opens a new avenue for functionalizing metallic glasses as a large-surface area and lightweight material for various structural and functional applications.

Many transition metals and alloys are expected to have high catalytic activities because of incompletely filled d orbitals for readily giving and taking electrons. However, the poor corrosion resistance, originating from high chemical activity, limits their applications as electrocatalysts for reactions in acidic and alkaline electrolytes. In this study, it is found that homogeneous amorphous structure can effectively decouple the intertangling catalytic activities and electrochemical stability of transition metal alloys. A noble-metal- free Ni40Fe40P20 metallic glass shows superior catalytic activities and high corrosion resistance, in comparison with the crystallized counterpart and other nanostructured noble-metal-based catalysts, for electrochemical water splitting in both acidic and alkaline solutions.

Barium silicate glasses with 0-40 mol% BaO were synthesized either by aerodynamical levitation and laser heating (at low barium content) or by conventional melting and quenching process. Characterization by means of Raman scattering spectroscopy and scanning transmission electron microscopy reveals a structural transition between glasses with low BaO content (<10 mol%) showing an atomic network resembling the one of amorphous silica, and glasses with a BaO content larger than 10 mol%, which exhibit the typical signature of a binary silicate glass with Q(2) and Q(3) units. Viscosity curves show a marked increase of the viscosity as the BaO content decreases below 20 mol%. Barium is found to easily diffuse and promote phase separation while silicon remains homogeneously distributed. A dramatic increase in the viscosity is observed as phase separation proceeds, resulting in the formation of Ba-rich nodules in a percolating SiO2-rich matrix at low barium content, or in Ba-poor nodules in a BaO-rich matrix at large barium content.

Next-generation high-performance structural materials are required for lightweight design strategies and advanced energy applications. Maraging steels, combining a martensite matrix with nanoprecipitates, are a class of high-strength materials with the potential for matching these demands(1-3). Their outstanding strength originates from semi-coherent precipitates(4,5), which unavoidably exhibit a heterogeneous distribution that creates large coherency strains, which in turn may promote crack initiation under load(6-8). Here we report a counterintuitive strategy for the design of ultrastrong steel alloys by high-density nanoprecipitation with minimal lattice misfit. We found that these highly dispersed, fully coherent precipitates (that is, the crystal lattice of the precipitates is almost the same as that of the surrounding matrix), showing very low lattice misfit with the matrix and high anti-phase boundary energy, strengthen alloys without sacrificing ductility. Such low lattice misfit (0.03 +/- 0.04 per cent) decreases the nucleation barrier for precipitation, thus enabling and stabilizing nanoprecipitates with an extremely high number density (more than 10(24) per cubic metre) and small size (about 2.7 +/- 0.2 nanometres). The minimized elastic misfit strain around the particles does not contribute much to the dislocation interaction, which is typically needed for strength increase. Instead, our strengthening mechanism exploits the chemical ordering effect that creates backstresses (the forces opposing deformation) when precipitates are cut by dislocations. We create a class of steels, strengthened by Ni(Al, Fe) precipitates, with a strength of up to 2.2 gigapascals and good ductility (about 8.2 per cent). The chemical composition of the precipitates enables a substantial reduction in cost compared to conventional maraging steels owing to the replacement of the essential but high-cost alloying elements cobalt and titanium with inexpensive and lightweight aluminium. Strengthening of this class of steel alloy is based on minimal lattice misfit to achieve maximal precipitate dispersion and high cutting stress (the stress required for dislocations to cut through coherent precipitates and thus produce plastic deformation), and we envisage that this lattice misfit design concept may be applied to many other metallic alloys.

A full-performance rechargeable Li-O-2 battery is developed by utilizing a nano-porous graphene cathode integrating with a compatible redox additive in a dimethyl sulfoxide based electrolyte. This battery system promotes the solution phase growth of Li2O2 for a large capacity and efficient decomposition of Li2O2 at a low charge potential, shining lights on practical implementations of Li-O-2 batteries for high energy applications.

The phase transition between semiconducting 1H to metallic 1T phases in monolayered transition metal dichalcogenides (TMDs) essentially involves three-dimensional (3D) structure changes of asymmetric relocations of S atoms at the top and bottom of the one unit-cell crystals. Even though the phase transition has a profound influence on properties and applications of 2D TMDs, a viable approach to experimentally characterize the stacking sequences of the vertically asymmetrical 1T phase is still not available. Here, we report an electron diffraction method based on dynamic electron scattering to characterize the stacking sequences of 1T MoS2 monolayers. This study provides an approach to unveil the 3D structure of 2D crystals and to explore the underlying mechanisms of semiconductor-to-metal transition of monolayer TMDs.

High-energy-density rechargeable Li-O-2 batteries are one of few candidates that can meet the demands of electric drive vehicles and other high-energy applications because of the ultra-high theoretical specific energy. However, the practical realization of the high rechargeable capacity is usually limited by the conflicted requirements for porous cathodes in high porosity to store the solid reaction products Li2O2 and large accessible surface area for easy formation and decomposition of Li2O2. Here we designed a hierarchical and bicontinuous nanoporous structure by introducing secondary nanopores into the ligaments of coarsened nanoporous gold by two-step dealloying. The hierarchical and bicontinuous nanoporous gold cathode provides high porosity, large accessible surface area and sufficient mass transport path for high capacity and long cycling lifetime of Li-O-2 batteries.

This article proposes a topological method that extracts hierarchical structures of various amorphous solids. The method is based on the persistence diagram (PD), a mathematical tool for capturing shapes of multiscale data. The input to the PDs is given by an atomic configuration and the output is expressed as 2D histograms. Then, specific distributions such as curves and islands in the PDs identify meaningful shape characteristics of the atomic configuration. Although the method can be applied to a wide variety of disordered systems, it is applied here to silica glass, the Lennard-Jones system, and Cu-Zr metallic glass as standard examples of continuous random network and random packing structures. In silica glass, the method classified the atomic rings as short-range and medium-range orders and unveiled hierarchical ring structures among them. These detailed geometric characterizations clarified a real space origin of the first sharp diffraction peak and also indicated that PDs contain information on elastic response. Even in the Lennard-Jones system and Cu-Zr metallic glass, the hierarchical structures in the atomic configurations were derived in a similar way using PDs, although the glass structures and properties substantially differ from silica glass. These results suggest that the PDs provide a unified method that extracts greater depth of geometric information in amorphous solids than conventional methods.

Solid silicon monoxide is an amorphous material which has been commercialized for many functional applications. However, the amorphous structure of silicon monoxide is a long-standing question because of the uncommon valence state of silicon in the oxide. It has been deduced that amorphous silicon monoxide undergoes an unusual disproportionation by forming silicon-and silicon-dioxide-like regions. Nevertheless, the direct experimental observation is still missing. Here we report the amorphous structure characterized by angstrom-beam electron diffraction, supplemented by synchrotron X-ray scattering and computer simulations. In addition to the theoretically predicted amorphous silicon and silicon-dioxide clusters, suboxide-type tetrahedral coordinates are detected by angstrom-beam electron diffraction at silicon/silicon-dioxide interfaces, which provides compelling experimental evidence on the atomic-scale disproportionation of amorphous silicon monoxide. Eventually we develop a heterostructure model of the disproportionated silicon monoxide which well explains the distinctive structure and properties of the amorphous material.

In this study, we report that the supercapacitor performance of polypyrrole (PPy) in non-aqueous electrolytes can be dramatically improved by highly conductive nanoporous gold which acts as both the support of active PPy and the current collector of supercapacitors. The excellent electronic conductivity, rich porous structure and large surface area of the nanoporous electrodes give rise to a high specific capacitance and low internal resistance in non aqueous electrolytes. Combining with a wide working potential window of similar to 2 V, the non-aqueous PPy-based supercapacitors show an extraordinary energy density and power density. (C) 2016 Elsevier Ltd. All rights reserved.

Precious metals (Pt and Pd) and rare earth elements (Ce in the form of CeO2) are typical materials for heterogeneous exhaust-gas catalysts in automotive systems. However, their limited resources and high market-driven prices are principal issues in realizing the path toward a more sustainable society. In this regard, herein, a nanoporous NiCuMnO catalyst, which is both abundant and durable, is synthesized by one-step free dealloying. The catalyst thus developed exhibits catalytic activity and durability for NO reduction and CO oxidation. Microstructure characterization indicates a distinct structural feature: catalytically active Cu/CuO regions are tangled with a stable nanoporous NiMnO network after activation. The results obtained by in situ transmission electron microscopy during NO reduction clearly capture the unique reaction-induced self-transformation of the nanostructure. This fi nding can possibly pave the way for the design of new catalysts for the conversion of exhaust gas based on the element strategy.

Li-O-2 batteries are a promising electrochemical energy-storage system with a sufficient energy density for all electric vehicles, with a one-charge driving distance comparable to conventional petrol cars. However, the practical implementations of Li-O-2 batteries face many scientific and technological challenges. Among these is the development of high-performance cathode materials that can provide high capacity, low charge/discharge overpotentials and stable cycling stability. Here, we report a nanoporous Ni cathode covered by N-doped graphene and self-grown catalyst for rechargeable Li-O-2 batteries. The novel hybrid cathode shows relatively low charge/discharge overpotentials, high volumetric capacity and long cycling lifetime, which may pave a new way for practical implementation of economic nanoporous metals as binder-free cathodes for high-performance Li-O-2 batteries.

Band gap engineering of monolayer transition metal dichalcogenides, such as MoS2 and WS2, is essential for the applications of the two-dimensional (2D) crystals in electronic and optoelectronic devices. Although it is known that chemical mixture can evidently change the band gaps of alloyed Mo1-xWxS2 crystals, the successful growth of Mo1-xWxS2 monolayers with tunable Mo/W ratios has not been realized by conventional chemical vapor deposition. Herein, we developed a low-pressure chemical vapor deposition (LP-CVD) method to grow monolayer Mo1-xWxS2 (x = 0-1) 2D crystals with a wide range of Mo/W ratios. Raman spectroscopy and high-resolution transmission electron microscopy demonstrate the homogeneous mixture of Mo and W in the 2D alloys. Photoluminescence measurements show that the optical band gaps of the monolayer Mo1-xWxS2 crystals strongly depend on the Mo/W ratios and continuously tunable band gap can be achieved by controlling the W or Mo portion by the LP-CVD.

Conductive polymers, particularly polypyrrole (PPy), are emerging as promising electrode materials for flexible supercapacitors because of their high pseudocapacitance, low density, high mechanical flexibility and low material costs. However, the practical implementations of PPy based supercapacitors have been prevented by the poor charge/discharge rate capability and low cycle stability. In this study we report a novel three dimensional interconnected nanotubular graphene-PPy (nt-GPPy) hybrid by incorporating PPy into highly conductive and stable nanoporous graphene. The bicontinuous nanotubular hybrid material with a large specific surface area and high conductivity demonstrates significant enhancement in supercapacitance performance of PPy in terms of high specific capacitance, excellent cycling stability and high rate capability. (C) 2015 Elsevier Ltd. All rights reserved.

Alloying is an important approach to improving catalytic activities and realizing new functions of heterogeneous catalysts, which has extensively been employed in fabricating noble metal based bimetallic catalysts. However, it is technically unviable in the synthesis of alloyed transition metal compounds, which are emerging as important catalysts for water splitting, in a controllable manner using conventional wet chemical methods. Here we report nanoporous bimetallic (Co1-xFex)(2)P phosphides with controllable compositions and tuneable porosity, which are fabricated by the combination of metallurgical alloy design and electrochemical etching. By tailoring the Co/Fe ratios and nanoporosity, the bimetallic phosphides exhibit versatile catalytic activities towards HER and OER in acidic and basic electrolytes. As both the cathode and the anode of an electrolyser, nanoporous (Co0.52Fe0.48)(2)P shows an outstanding performance in water electrolysis, comparable to the commercial electrolyser with paired Pt/C and IrO2 catalysts.

Single-atom nickel dopants anchored to three-dimensional nanoporous graphene can be used as catalysts of the hydrogen evolution reaction (HER) in acidic solutions. In contrast to conventional nickel-based catalysts and graphene, this material shows superior HER catalysis with a low over-potential of approximately 50 mV and a Tafel slope of 45 mV dec(-1) in 0.5 M H2SO4 solution, together with excellent cycling stability. Experimental and theoretical investigations suggest that the unusual catalytic performance of this catalyst is due to sp-d orbital charge transfer between the Ni dopants and the surrounding carbon atoms. The resultant local structure with empty C-Ni hybrid orbitals is catalytically active and electrochemically stable.

Freestanding nanoporous N-doped graphenewith encapsulated RuO2 nanoparticles is developed as a cathode for rechargeable Li-O-2 batteries. The stabilized metal oxide catalyst reduces charge overpotentials enabling high-efficiency rechargeable Li-O-2 batteries with a long cycling lifetime. This has important implications for the development of highly stable and catalytically active graphene-based cathodes for rechargeable Li-O-2 batteries.

We report a novel multicomponent mixed-valence oxyhydroxide-based electrode synthesized by electrochemical polarization of a de-alloyed nanoporous NiCuMn alloy. The multicomponent oxyhydroxide has a high specific capacitance larger than 627Fcm(-3) (1097 +/- 95Fg(-1)) at a current density of 0.25Acm(-3), originating from multiple redox reactions. More importantly, the oxyhydroxide electrode possesses an extraordinarily wide working-potential window of 1.8V in an aqueous electrolyte, which far exceeds the theoretically stable window of water. The realization of both high specific capacitance and high working-potential windows gives rise to a high energy density, 51mWhcm(-3), of the multicomponent oxyhydroxide-based supercapacitor for high-energy and high-power applications.

The characterization of the medium-range (MRO) order in amorphous materials and its relation to the short-range order is discussed. A new topological approach to extract a hierarchical structure of amorphous materials is presented, which is robust against small perturbations and allows us to distinguish it from periodic or random configurations. This method is called the persistence diagram (PD) and introduces scales to many-body atomic structures to facilitate size and shape characterization. We first illustrate the representation of perfect crystalline and random structures in PDs. Then, the MRO in amorphous silica is characterized using the appropriate PD. The PD approach compresses the size of the data set significantly, to much smaller geometrical summaries, and has considerable potential for application to a wide range of materials, including complex molecular liquids, granular materials, and metallic glasses.

A potential energy landscape (PEL) gives rise to diverse non-equilibrium dynamics in complex systems. In this study, we visualize the topological landscape of a steady-state flow under shear deformation in a model metallic glass. We use the "state space network" as the best predictor of state transitions in terms of statistical model selection. The proposed scheme visualizes the underlying PEL regarding a transitions associated with irreversible cage-breaking events as the cooperative motion of clusters. By characterizing the topological property of the state space network, we observe characteristics of a small-world network. The proposed scheme has a significant potential to enable the understanding of the underlying mechanisms of glass physics, and is analogous to biological networks. Copyright (C) EPLA, 2015

For observations of crystalline nanoclusters, the features and capabilities of depth-resolution imaging by aberration-corrected transmission electron microscopy (TEM) were investigated using image simulations and experiments for two types of samples. The first sample was gold clusters attached on an amorphous carbon film. The experimental through-focal series indicated that the focal plane for the cluster was shifted 3 nm from that for the supporting film. This difference is due to the depth-resolution imaging of the cluster and film, the mid-planes of which are separated by 3 nm along the depth direction (the electron incident direction). On the basis of this information, the three-dimensional configuration of the sample, such as the film thickness of 2 nm, was successfully illustrated. The second sample was a Zr66.7Ni33.3 metallic glass including a medium-range-order (MRO) structure, which was approximately considered to be a crystalline cluster with a diameter of 1.6 nm, In the experimental through local series, the lattice fringe of the MRO cluster was visible at limited focal conditions. Image simulations reproduced well the focal conditions and also indicated a structural condition for the visualization that the embedded cluster must be apart from the mid plane of the matrix film. Similar to the case of the first sample, this result can be explained by the idea that the "effective focal planes" for the film and cluster are at different heights. This type of depth resolution phase contrast imaging is possible only in aberration-corrected TEM and when the sample has a simple structure and is sufficiently thin for the kinematical scattering approximation. (C) 2014 Elsevier B.V. All rights reserved.

Lithium-ion batteries (LIBs) have been intensively studied to meet the increased demands for the high energy density of portable electronics and electric vehicles. The low specific capacity of the conventional graphite based anodes is one of the key factors that limit the capacity of LIBs. Transition metal oxides, such as NiO, MnO2 and Fe3O4, are known to be promising anode materials that are expected to improve the specific capacities of LIBs for several times. However, the poor electrical conductivity of these oxides significantly restricts the lithium ion storage and charge/discharge rate. Here we report that dealloyed nanoporous metals can realize the intrinsic lithium storage performance of the oxides by forming oxide/metal composites. Without any organic binder, conductive additive and additional current collector, the hybrid electrodes can be directly used as anodes and show highly reversible specific capacity with high-rate capability and long cyclic stability.

The "edge-free" monolayer MoS2 films supported by 3D nanoporous gold show high catalytic activities towards hydrogen evolution reaction (HER), originating from large out-of-plane strains that are geometrically required to manage the 3D curvature of bicontinuous nano porosity. The large lattice bending leads to local semiconductor-to-metal transition of 2H MoS2 and the formation of catalytically active sites for HER.

Grain rotation is a well-known phenomenon during high (homologous) temperature deformation and recrystallization of polycrystalline materials. In recent years, grain rotation has also been proposed as a plasticity mechanism at low temperatures (for example, room temperature for metals), especially for nanocrystalline grains with diameter d less than similar to 15 nm. Here, in tensile-loaded Pt thin films under a high-resolution transmission electron microscope, we show that the plasticity mechanism transitions from cross-grain dislocation glide in larger grains (d> 6 nm) to a mode of coordinated rotation of multiple grains for grains with d< 6 nm. The mechanism underlying the grain rotation is dislocation climb at the grain boundary, rather than grain boundary sliding or diffusional creep. Our atomic-scale images demonstrate directly that the evolution of the misorientation angle between neighbouring grains can be quantitatively accounted for by the change of the Frank-Bilby dislocation content in the grain boundary.

Dealloyed nanoporous metals have attracted much attention because of their excellent catalytic activities toward various chemical reactions. Nevertheless, coarsening mechanisms in these catalysts have not been experimentally studied. Here, we report in situ atomic-scale observations of the structural evolution of nanoporous gold during catalytic CO oxidation. The catalysis-induced nanopore coarsening is associated with the rapid diffusion of gold atoms at chemically active surface steps and the surface segregation of residual Ag atoms, both of which are stimulated by the chemical reaction. Our observations provide the first direct evidence that planar defects hinder nanopore coarsening, suggesting a new strategy for developing structurally stable and highly active heterogeneous catalysts.

A compact 120-GHz-band finline orthomode transducer (OMT) with high isolation between orthogonal ports (I-op) was designed and fabricated for bidirectional wireless data transmission with polarization multiplexing. To achieve high I-op, finline OMTs normally use a resistive card to decrease unwanted resonance, that occurs on the finline, but adding a resistive card complicates the fabrication process and raises the cost of fabrication. Our proposed finline OMT uses an improved finline design in which the resonance frequency is controlled in order to expel unwanted resonance from the operation bandwidth of the 120-GHz-band wireless link. The proposed finline design enables high I-op without using a resistive card, which simplifies the fabrication process and lowers the cost of fabrication. A square horn antenna, which is attached to the finline OMT, is also designed to suppress unwanted polarization rotation of reflected waves, which further improves I-op. The proposed finline OMT has a transmission loss of less than 1.2 dB, return loss of more than 12 dB, cross polarization discrimination of more than 30 dB, and I-op of more than 50 dB across the entire occupied bandwidth of the 120-GHz-band wireless link. These characteristics are sufficient not only for 10-Gbit/s bidirectional data transmission but also for 20-Gbit/s unidirectional 2-ch data transmission by polarization-multiplexing.

A binder-free self-grown oxy-hydroxide@ nanoporous Ni-Mn hybrid electrode with high capacitance and cyclic stability is fabricated by electrochemical polarization of a dealloyed nanoporous Ni-Mn alloy. Combined with the low material costs, high electrochemical stability, and environmentally friendly nature, this novel electrode holds great promise for applications in high-capacity commercial supercapacitors.

Superhard materials consisting of light elements have recently received considerable attention because of their ultrahigh specific strength for a wide range of applications as structural and functional materials. However, the failure mechanisms of these materials subjected to high stresses and dynamic loading remain to be poorly known. We report asymmetric twins in a complex compound, boron carbide (B4C), characterized by spherical-aberration-corrected transmission electron microscopy. The atomic structure of boron-rich icosahedra at rhombohedral vertices and cross-linked carbon-rich atomic chains can be clearly visualized, which reveals unusual asymmetric twins with detectable strains along the twin interfaces. This study offers atomic insights into the structure of twins in a complex material and has important implications in understanding the planar defect-related failure of superhard materials under high stresses and shock loading. (C) 2014 AIP Publishing LLC.

We prepared one-unit-cell (1-UC) thick FeSe films on insulating SrTiO3 substrates with non-superconducting FeTe protection layers by molecular beam epitaxy for ex situ studies. By direct transport and magnetic measurements, we provide definitive evidence for high temperature superconductivity in the 1-UC FeSe films with an onset T-C above 40K and an extremely large critical current density J(C) similar to 1.7x10(6) A/cm(2) at 2 K, which are much higher than T-C similar to 8K and J(C)similar to 10(4) A/cm(2) for bulk FeSe, respectively. Our work may pave the way to enhancing and tailoring superconductivity by interface engineering.

The production of two-dimensional rhenium disulfide (ReS2) nanosheets by exfoliation using lithium intercalation is demonstrated. The vibrational and photoluminescence properties of the exfoliated nanosheets are investigated, and the local atomic structure is studied by scanning and transmission electron microscopy. The catalytic activity of the nanosheets in a hydrogen evolution reaction (HER) is also investigated. The electrochemical properties of the exfoliated ReS2 nanosheets include low overpotentials of similar to 100 mV and low Tafel slopes of 75 mV dec(-1) for HER and are attributed to the atomic structure of the superlattice 1T' phase. The presence of bandgap photoluminescence demonstrates that the nanosheets retain their semiconducting nature. ReS2 nanosheets produced by this method provide unique photocatalytic properties that are superior to those of other two-dimensional systems.

We have developed an Angstrom-beam electron diffraction (ABED) technique for structure characterization of amorphous materials using a state-the-of-art spherical aberration-corrected scanning transmission electron microscope. The focused electron beam with a diameter of similar to 0.4 nm, comparable to the size of short range order in glasses, enables us to directly detect local atomic structure of disordered materials in a diffraction mode. In this paper we briefly introduce the basic principle of ABED and preliminary applications in structural characterization of metallic glasses and oxide glasses. We also discuss the effect of sample thickness and the method to study medium range order of glassy materials using ABED. (C) 2013 Elsevier B.V. All rights reserved.

Composition-controlled fabrication of bimetallic catalysts is of significance in electrochemical energy conversion and storage. A novel nanoporous Pt-Cu bimetallic catalyst with a Pt skin and a Pt-Cu core, fabricated by electrochemically dealloying a bulk Pt-Cu binary alloy using a potential-controlled approach, is reported. The Pt/Cu ratio of the dealloyed nanoporous catalyst can be readily adjusted in a wide composition range by only controlling dealloying potential. The electro-catalytic performance of the nanoporous Pt-Cu catalyst shows evident dependence on Pt/Cu ratio although the surfaces of all the nanoporous catalysts are characterized to be covered by pure Pt. With optimal compositions, the dealloyed nanoporous Pt-Cu catalyst possesses enhanced electrocatalytic activities toward oxygen reduction reaction and formic acid oxidation in comparison with the commercial Pt/C catalyst.

The elastic strain sustainable in crystal lattices is usually limited by the onset of inelastic yielding mediated by discrete dislocation activity, displacive deformation twinning and stress-induced phase transformations, or fracture associated with flaws. Here we report a continuous and gradual lattice deformation in bending nickel nanowires to a reversible shear strain as high as 34.6%, which is approximately four times that of the theoretical elastic strain limit for unconstrained loading. The functioning deformation mechanism was revealed on the atomic scale by an in situ nanowire bending experiments inside a transmission electron microscope. The complete continuous lattice straining process of crystals has been witnessed in its entirety for the straining path, which starts from the face-centred cubic lattice, transitions through the orthogonal path to reach a body-centred tetragonal structure and finally to a re-oriented face-centred cubic structure.

Precisely probing heavy metal ions in water is important for molecular biology, environmental protection, and healthy monitoring. Although many methods have been reported in the past decade, developing a quantitative approach capable of detecting sub-ppt level heavy metal ions with high selectivity Is still challenging. Here we report an extremely sensitive and highly selective nanoporous gold/aptamer based surface enhanced resonance Raman scattering (SERRS) sensor. The optical sensor has an unprecedented detection sensitivity of 1 pM (0.2 ppt) for Hg2+ ions, the most sensitive Hg2+ optical sensor known so far. The sensor also exhibits excellent selectivity. Dilute Hg2+ ions can be identified in an aqueous solution containing 12 metal ions as well as in river water and underground water. Moreover, the SERRS sensor can be reused without an obvious loss of the sensitivity and selectivity even after 10 cycles.

Precipitate size and number density are two key factors for tailoring the mechanical behavior of nanoscale precipitate-hardened alloys. However, during thermal aging, the precipitate size and number density change, leading to either poor strength or high strength but significantly reduced ductility. Here we demonstrate, by producing nanoscale co-precipitates in composition-optimized multicomponent precipitation-hardened alloys, a unique approach to improve the stability of the alloy against thermal aging and hence the mechanical properties. Our study provides compelling experimental evidence that these nanoscale co-precipitates consist of a Cu-enriched bcc core partially encased by a B2-ordered Ni( Mn, Al) phase. This co-precipitate provides a more complex obstacle for dislocation movement due to atomic ordering together with interphases, resulting in a high yield strength alloy without sacrificing alloy ductility.

Hybrid structures combining fullerenes and carbon nanotubes have exhibited exciting properties. However, the low efficiency and complex process of such assembly restrict their practical applications. We report a single-step procedure to synthesize the fullerene-intercalated (including endohedral metallofullerene (Y@Cn)) porous carbon nanofibers (pCNFs) by chemical vapor deposition (CVD) using a Fe/Y catalyst on a copper substrate. Fullerenes were simultaneously synthesized with the pCNF growth during the CVD process. Instead of attaching them on the surface of the CNFs, the fullerenes were inserted in the graphitic interlayer spacing, inducing micro- and mesopores in CNFs. The growth mechanism of the fullerene-intercalated pCNFs was discussed. (C) 2012 Elsevier Ltd. All rights reserved.

Distinct from inert bulk gold, nanoparticulate gold has been found to possess remarkable catalytic activity towards oxidation reactions. The catalytic performance of nanoparticulate gold strongly depends on size and support, and catalytic activity usually cannot be observed at characteristic sizes larger than 5 nm. Interestingly, significant catalytic activity can be retained in dealloyed nanoporous gold (NPG) even when its feature lengths are larger than 30 nm. Here we report atomic insights of the NPG catalysis, characterized by spherical-aberration-corrected transmission electron microscopy (TEM) and environmental TEM. A high density of atomic steps and kinks is observed on the curved surfaces of NPG, comparable to 3-5 nm nanoparticles, which are stabilized by hyperboloid-like gold ligaments. In situ TEM observations provide compelling evidence that the surface defects are active sites for the catalytic oxidation of CO and residual Ag stabilizes the atomic steps by suppressing {111} faceting kinetics.

Metal/organic-molecule/metal nanoscale junctions, which consist of poly(3-hexylthiophene):6,6-phenyl C61-butyric acid methyl ester (P3HT:PCBM) organic molecules sandwiched between two Ni thin films whose edges are crossed, which are called quantum cross (QC) devices, have been fabricated and their structural and electrical properties have been investigated. The area of the crossed section, which was obtained without using electron-beam or optical lithography, can be as small as 16 x 16 nm(2). We have obtained ohmic current-voltage characteristics, which show quantitative agreement with the theoretical calculation results performed within the framework of the Anderson model under the strong coupling limit. Calculation results also predict that a high on-off ratio beyond 100000 : 1 can be obtained in Ni/P3HT:PCBM/Ni QC devices under the weak coupling condition. These results indicate that our method utilizing thin-film edges is useful for creating nanoscale junctions and Ni/P3HT:PCBM/Ni QC devices can be expected to have potential application in next-generation switching devices with high on-off ratios. (c) 2012 The Japan Society of Applied Physics

Nanostructured ferritic alloys (NFAs) have been essentially fabricated by mechanical alloying pre-alloyed ferritic powders with Y2O3. In this work, Y2O3 was replaced by Y hydride and more soluble Fe2O3 to prepare NFAs. The microstructural characterization concerning the formation of nanoparticles and mechanical property of NFAs prepared by the novel process were investigated. It is found, during mechanical alloying both Fe2O3 and hydride can be easily dissolved into the ferritic matrix. Coherent Y-Ti-O nanoparticles with a pyrochlore Y2Ti2O7 structure and incoherent Cr-rich oxides were precipitated after the hot consolidation. With an increased milling time, there exists a shift of oxygen from the Cr-rich oxides to Y-Ti-O nanoparticles, resulting in a significantly homogeneous dispersion of nanoparticles. Compared with 14YWT, the NFAs in this work show a combination of high strength and improved ductility. Thus, the addition of Fe2O3 as an oxygen carrier provides an alternate way to adjust the oxygen content, which does not require high energy milling; and the combination of hot forging and hot rolling processes, rather than the hot extrusion are more cost-effective. (C) 2012 Elsevier B.V. All rights reserved.

Studies on radiation-induced structural changes of solids are of technological importance for realizing desirable material properties and for predicting the fate of materials under radiation environments. It is known that energetic particles, such as electrons, neutrons, and ions, produce extensive damage, and may eventually lead to amorphization. Amorphization is often accompanied with significant volume changes and concomitant microcracking. To clarify the amorphization mechanism, knowledge of amorphous structures is required. Radial distribution function analysis is one of the useful ways to characterize topological and chemical disorder in amorphous networks. Here, we review the advantage of electron diffraction for analyzing short-range order of amorphous materials and show some examples of radial distribution functions obtained by our group. (C) 2011 Elsevier B.V. All rights reserved.

A nanoporous PdNi (np-PdNi) bimetallic catalyst fabricated by electrochemically dealloying a Pd20Ni80 alloy in an acid solution is reported. Residual Ni in the nanoporous alloy can be controlled by tuning dealloying potentials and the electrocatalysis of the np-PdNi shows evident dependence on Ni concentrations. With similar to 9 at.% Ni, the np-PdNi bimetallic catalyst presents superior electrocatalytic performances in methanol and formic acid electro-oxidation as well as oxygen reduction in comparison with commercial Pd/C and nanoporous Pd (np-Pd). The excellent electrocatalytic properties of the dealloyed np-PdNi bimetallic catalyst appear to arise from the combined effect of unique bicontinuous nanoporosity and bimetallic synergistic action.

Nanoporous gold films containing various amounts of residual silver have been synthesized by controllable dealloying and subsequent annealing for surface-enhanced Raman scattering (SEAS). It was found that the residual Ag plays an important role in the SERS effect of dealloyed nanoporous gold. More residual Ag gives rise to better SERS effects when nanopore sizes are nearly identical. Moreover, homogenization of the residual silver by annealing can further improve the SERS enhancement of nanoporous Au-Ag alloys.

Zr-doped sodium titanate nanobelts were obtained by a hydrothermal treatment of TiO2 powder on Ti-based bulk metallic glass (BMG). The latest aberration-correction techniques were used to determine the atomic structure of Zr-doped sodium titanate nanobelts. The nanobelts were found to exhibit a structural modulation by the periodic Zr substitution of Ti atoms at 1.75 nm intervals. Systematic density-functional theory (DFT) calculations confirmed the optimized atomic arrangement in consistency with the experimental results, and a reduction of the band gap value could possibly enhance the characteristics of the materials used in a variety of circumstances. (C) 2011 The Japan Society of Applied Physics

Amplified by plasomonic nanostructured metals, Raman intensity of organic molecules and biomolecules can be dramatically improved, particularly at "hot spots" where intense electromagnetic fields are produced in the vicinity of narrow nanogaps between metallic nanostructures. Therefore, developing new substrates with a high density of "hot spots" has been the recent topic of Intense study. Here we report wrinkled nanoporous gold films that contain abundant Raman-active nanogaps produced by deformation and fracture of nanowire-like gold ligaments. This novel nanostructure yields ultrahigh surface enhanced Raman scattering for molecule detection.

Electrochemical supercapacitors can deliver high levels of electrical power and offer long operating lifetimes(1-8), but their energy storage density is too low for many important applications(2,3). Pseudocapacitive transition-metal oxides such as MnO2 could be used to make electrodes in such supercapacitors, because they are predicted to have a high capacitance for storing electrical charge while also being inexpensive and not harmful to the environment(9,10). However, the poor conductivity of MnO2 (10(-5)-10(-6) S cm(-1)) limits the charge/discharge rate for high-power applications(10,11). Here, we show that hybrid structures made of nanoporous gold and nanocrystalline MnO2 have enhanced conductivity, resulting in a specific capacitance of the constituent MnO2 (similar to 1,145 F g(-1)) that is close to the theoretical value(9). The nanoporous gold allows electron transport through the MnO2, and facilitates fast ion diffusion between the MnO2 and the electrolytes while also acting as a double-layer capacitor. The high specific capacitances and charge/discharge rates offered by such hybrid structures make them promising candidates as electrodes in supercapacitors, combining high-energy storage densities with high levels of power delivery.

The determination of the atomic configuration of metallic glasses is a long-standing problem in materials science and solid-state physics(1,2). So far, only average structural information derived from diffraction and spectroscopic methods has been obtained. Although various atomic models have been proposed in the past fifty years(3-8), a direct observation of the local atomic structure in disordered materials has not been achieved. Here we report local atomic configurations of a metallic glass investigated by nanobeam electron diffraction combined with ab initio molecular dynamics simulation. Distinct diffraction patterns from individual atomic clusters and their assemblies, which have been theoretically predicted as short- and medium-range order(6-8), can be experimentally observed. This study provides compelling evidence of the local atomic order in the disordered material and has important implications in understanding the atomic mechanisms of metallic-glass formation and properties.

Formation behavior of nanovoids during the annealing of amorphous Al2O3 and WO3 was studied by transmission electron microscopy. The density and size of the voids in Al2O3 and WO3 increase with increasing annealing temperature from 973 to 1123 K and from 573 to 673 K, respectively. It is suggested that the formation of nanovoids during annealing is attributed to the large difference in density between as-deposited amorphous and crystalline oxides.

Nanoscale structural information of amorphous structures has become obtainable by using nanobeam electron diffraction in combination with high resolution imaging. In addition, accurate radial distribution function analysis using energy filter has also become available to know averaged amorphous structures. In this paper, we introduce some applications of these techniques, especially to several Fe-based metallic glasses. On the basis of these results, we discuss a relationship between the glass structure and the glass stability in Fe-based metallic glasses

Nanoscale quasicrystal-like structural states have been found in the course of crystallization in an Fe-based Fe48Cr15Mo14C15B6Tm2 bulk metallic glass. The quasicrystal-like structure is similar with the chi-FeCrMo structure exhibiting a deformed tenfold diffraction pattern due to projected pentagonal arrangements regarded as a Mo framework. We show the preliminary structural model for the quasicrystal-like structure and discuss the three-dimensional features based on the chi-FeCrMo crystalline approximant. (C) 2010 Elsevier B.V. All rights reserved.

Quantum cross (QC) devices which consist of two Ni thin films deposited on polyethylene naphthalate substrates with their edges crossing have been fabricated and their current-voltage characteristics have been investigated. The cross-sectional area between the two Ni electrodes, which was obtained without the use of electron-beam or optical lithography, can be as small as 17 nm x 17 nm. We have successfully obtained ohmic current-voltage characteristics, which show good agreement with calculation results within the framework of the modified Anderson model. The calculated results also predict a high switching ratio in excess of 100000:1 for QC devices having the molecule sandwiched between the Ni electrodes. This indicates that QC devices having the molecule can be expected to have potential application in novel switching devices.

Crystallization behaviours around the glass transition temperature in an amorphous Fe(70)Nb(10)B(20) alloy were investigated by means of transmission electron microscopy. Dense bcc-Fe nanocrystals initially appeared as the primary phase, followed by the dense formation of the (Fe,Nb)(23)B(6) nanocrystalline phase. The bcc-Fe nanocrystals were formed even by annealing at a temperature that is 38 K lower than the glass transition temperature. A difference of the low temperature behaviours between the present conventional amorphous alloy and a bulk metallic glass was discussed. (C) 2009 Elsevier Ltd. All rights reserved.

We have found nanoscale quasicrystal-like structural states exhibiting pseudotenfold nanobeam electron-diffraction patterns in the course of nanocrystallization process of an Fe23B6 structure in an (Fe0.5Co0.5)(72)B20Si4Nb4 metallic glass. An existence of the intermediate states between the quasicrystal-like and Fe23B6 structures indicates that the quasicrystal-like structure is approximate to the Fe(23)B(6)structure including no icosahedral atomic arrangement. The pseudotenfold electron-diffraction patterns are understood from a combination of three types of tiles found in the Fe23B6 structure. The three types of tiles can produce decagonal units which do not have any icosahedral atomic arrangement.

NiO heterostructured nanowires are promising building blocks due to the nonvolatile resistive switching in nanoscale. Here, we report on the noncontact transport measurements of single crystalline NiO/MgO heterostructured nanowires by utilizing a microwave conductivity method. We found the substantial discrepancy up to four orders of magnitude between the heterostructured nanowires and heterothin films on the resistivity when the bulk resistivity increased, whereas the reasonable agreement was found for relatively conductive range. The origin of such huge discrepancy was interpreted in terms of both the large specific surface area of nanowires and the surface transport events of insulative NiO. (C) 2009 American Institute of Physics. [doi:10.1063/1.3237176]

Local structural fluctuation in relation to the medium range order (MRO) in a Pd-Ni-P bulk metallic glass was examined using nanobeam, electron diffraction (NBED) technique. We found diffraction spots with strong intensities in the NBED patterns taken from any observation sites in the specimen. This indicates a presence of MRO regions densely formed in the specimen. The diffraction spots in NBED were normally dispersed around positions corresponding to the first halo-diffraction ring in selected area diffraction. A low-temperature annealing led to form a nanocrystalline microstructure consisting of unidentified phosphides. In the course of annealing, the MRO structures deduced from the NBED patterns have no structural similarity to the phosphides found in the primary crystallization stage. The MRO structure changes into a similar structure with the primary crystals just before the crystallization. A discussion is made for the MRO structure and its relation to the glass stability and also to the phosphide nucleation in the primary crystallization. (C) 2008 Elsevier B.V. All rights reserved.

Local structure changes on annealing of soft magnetic Fe(76)Si(9)B(10)P(5) metallic glass was examined using transmission electron microscopy. Medium-range order regions in glass states were clearly developed on annealing for structural relaxation below the glass-transition temperature which leads a decrease of magnetic coercivity as well as a physical density. Nanobeam electron diffraction analysis revealed that the medium-range order structure developed on annealing has no structural order of the primary crystal with a long-period complex structure. The relaxed glass can be regarded as a specific state which is characterized by medium-range order structures. (C) 2008 Published by Elsevier Ltd.

We study the structural properties of the surface roughness, the surface mound size and the interfacial structure in Ni thin films vacuum-deposited on polyethylene naphthalate (PEN) organic substrates with and without the application of magnetic field and discuss its feasibility of fabricating quantum cross (QC) devices. For Ni/PEN evaporated without the magnetic field, the surface roughness decreases from 1.3 nm to 0.69 nm and the surface mound size increases from 32 nm to 80 nm with the thickness increased to 41 nm. In contrast, for Ni/PEN evaporated in the magnetic field of 360 Oe, the surface roughness tends to slightly decrease from 1.3 nm to 1.1 nm and the surface mound size shows the almost constant value of 28-30 nm with the thickness increased to 35 nm. It can be also confirmed for each sample that there is no diffusion of Ni into the PEN layer, resulting in clear Ni/PEN interface and smooth Ni surface. Therefore, these experimental results indicate that Ni/PEN films can be expected as metal/insulator hybridmaterials in QC devices, leading to novel high-density memory devices. (C) 2008 Elsevier B.V. All rights reserved.

We have found nanoscale metastable state with a chi-FeCrMo-like structure exhibiting pseudotenfold diffraction pattern in the course of crystallization in an Fe-based Fe(48)Cr(15)Mo(14)C(15)B(6)Tm(2) bulk metallic glass with a high glass stability. All the diffraction spots were found along the first and second halo rings of the glass structure. It was also found that the diffraction pattern with the pseudotenfold symmetry changed into the [113] zone-axis pattern of the chi-FeCrMo structure. On the basis of the results, we discussed local atomic arrangements of this metastable state in relation to the glass stability.

The crystallization process in an Fe48Cr15Mo14C15B6Tm2 metallic glass has been investigated by means of nanobeam and selected area electron-diffraction techniques. We found that the first crystallization reaction proceeds through a complicated nanoscale process, that is, amorphous -&gt;chi-FeCrMo-like long-period structures -&gt;chi-FeCrMo -&gt; M23C6. A long-period structure began forming as an extended structure of medium range order; its periodicity gradually changed with the growing stage on annealing, and the structure finally changed into chi-FeCrMo. The common structural unit among these structures was found to be an atomic coordination polyhedron with a coordination number of 16. On the basis of the results, we discuss the phase stability of the Fe48Cr15Mo14C15B6Tm2 metallic glass as well as its local atomic arrangements.

Thermally induced structural relaxation in amorphous silicon carbide (SiC) has been examined by means of in situ transmission electron microscopy (TEM). The amorphous SiC was prepared by high-energy ion beam irradiation into a single crystalline 4H-SiC substrate. Cross-sectional TEM observations and electron energy-loss spectroscopy measurements revealed that thermal annealing induces a remarkable volume reduction, so-called densification, of amorphous SiC. From radial distribution function analyses using electron diffraction, notable changes associated with structural relaxation were observed in chemical short-range order. It was confirmed that the structural changes observed by the in situ TEM study agree qualitatively with those of the bulk material. On the basis of the alteration of chemical short-range order, we discuss the origin of thermally induced densification in amorphous SiC. (C) 2008 American Institute of Physics.

Local structural development in the bulk metallic glass (Fe0.5Co0.5)(72)B20Si4Nb4 on annealing has been investigated using transmission electron microscopy. Nanoscale crystalline grains with the Fe23B6-type structure were densely formed during annealing around the first crystallization temperature. In the state prior to the crystallization (below T-g), we found extended medium range ordered (MRO) regions as small as 2 nm with an extremely high density in the glass matrix. The nanocrystallized microstructure is presumably ascribed to the presence of the dense MRO regions. On the basis of nanobeam diffraction analysis, however, it was found that most of the MRO regions have no clear order of the Fe23B6-type structure. The clear Fe23B6 order was found in regions extending as large as 5 nm at a higher temperature (around Tg). A relationship between the structural change and the glass stability is discussed. (C) 2008 Published by Elsevier Ltd.

The structural correspondence among the bcc, ordered-bcc B2, triclinic Al(2)Fe and approximant Al(5)Fe(2) structures have been examined on the basis of the experimentally obtained orientation relationship of (110)(bcc,B2) //(2 (2) over bar1)(Al2Fe) and [(1) over bar 11](bcc,B2) // N(241)(Al2Fe), where N(hkl) denotes the normal direction of the (hkl) plane. The formation of the triclinic Al(2)Fe structure from the bcc structure is directly associated with that of Al-Fe covalent bonds; that is, hybridization between Al and Fe atoms. The covalent bond formation results in the appearance of decagonal-like atomic arrangements in the Al(2)Fe structure, which are similar to those in the approximant Al(5)Fe(2) structure.

Local atomic structures of Pd- and Fe-based metallic glasses (Pd 40Ni4OP2O and Fe84Nb 7B9)WeFe investigated by means of transmission electron microscopy (TEM). In these typical metallic glasses, local structures of nanoscale phase separation were observed using high-resolution TEM and nanobeam electron diffraction. A structural modeling of the Pd-based metallic glass with the observed local structures was also performed with the help of computer simulation which explained an energy-filtered electron diffraction data. The obtained results show that the comprehensive TEM study is useful to understand nanoscale structural organizations in metallic glasses.

Local atomic structures of rapidly quenched amorphous Fe100-xBx(x = 14,17,20) alloys have been investigated comprehensively by means of high-resolution electron microscopy (HREM), nanobeam electron diffraction (NBED), and electron diffraction atomic pair distribution function (PDF) analysis. In HREM images, crystalline cluster regions with a bcc-Fe structure extending as small as 1 nm were observed locally as lattice images, while NBED with a probe size as small as 1 nm revealed an existence of local clusters with structures of bcc-Fe and also of Fe-boride in all the as-formed alloys. Atomic PDF analyses were performed for these alloys by precise measurements of halo-electron diffraction intensities using imaging-plate and energy-filtering techniques. From the interference functions, atomic structure models were constructed for the Fe-B amorphous structures with the help of reverse Monte Carlo calculation. From Voronoi polyhedral analysis applied to these structure models, it was confirmed that atomic polyhedral arrangements with bcc and icosahedral clusters of Fe, and trigonal prisms of Fe and B, are formed in these amorphous structures, and the fraction of bcc-Fe clusters increases with the Fe content, while the fraction of trigonal prisms increases with the B content. The direct observation of local cluster structures of bcc-Fe and Fe-boride by HREM and NBED is an indication of "nanoscale phase separation" driven in the course of amorphous formation of these alloys, and the constructed structures based on the experimental PDFs with different B contents are inconsistent with a local structure scheme expected from the "nanoscale phase separation" model. The present study demonstrates that the structure model of nanoscale phase separation stands for the amorphous alloy structures where the phase separation fatally occurs in the crystallization stage.

TbFe2D3.8, TbNi2D2.4, CuZr2 and NiZr2 metallic glasses have been studied to elucidate the structural characteristics by taking advantage of neutron and X-ray diffraction and using the reverse Monte Carlo (RMC) modeling based on the diffraction data. Topologically, about 98% of D atoms occupy tetrahedral sites formed by metal atoms for TbFe2D3.8 and TbNi2D2.4 metallic glasses. The Volonoi analysis of the structure of CuZr2 and NiZr2 metallic glasses was carried out to elucidate the relationship between the stability of glassy state and the atomic configuration. The prismatic-like polyhedra dominate in NiZr2 metallic glass. In contrast, the icosahedron-like polyhedra faces are preferred for constructing the structure of CuZr2 metallic glass. (c) 2006 Elsevier B.V. All rights reserved.

To understand the mechanism of the high number density of bcc-Fe nanocrystals in a partially crystallized Fe84Nb7B9 alloy, we have investigated detailed local structural and compositional changes on annealing amorphous ribbons using transmission electron microscopy, three-dimensional atom probe, and high-energy x-ray diffraction techniques. Nanobeam electron diffraction patterns from an as-quenched amorphous ribbon indicated a local nanoscale atomic ordering. On annealing, reduced interference functions showed a clear change just below the crystallization temperature (similar to 773 K). At this stage, local compositional fluctuations started to appear, and medium-range ordering with a bcc-Fe structure as small as 2 nm was clearly observed in high-resolution electron micrographs with an extremely high number density. Pair distribution function analyses suggested a structural change at this stage of annealing to increase the chemical bonds in the residual amorphous matrix around the bcc-Fe regions. The increase of atomic chemical bonds in the residual amorphous matrix is considered to retard the growth of the bcc-Fe nanocrystals after the coalescence of bcc-Fe MRO regions in the later stage of annealing. These results suggest that bcc-Fe nanocrystallization with the extremely high number density is ascribed to primarily (i) the presence of highly dense bcc-Fe MRO regions and (ii) the increase of chemical bonds of matrix atoms on annealing.

Possible structural units of the Fe7Mo6-type crystal structure in alloys, which is often called the mu structure, have been discussed on the basis of a formation process of the mu structure in an Fe-Mo alloy. A disordered decagonal-column state appeared in the initial stage where locally ordered regions of column blocks consisting of four decagonal columns existed. A column-block layer in the mu structure can also be formed by a one-dimensional connection of the same column blocks. The atomic column block can be assigned as one of the structural units in alloys.

The structures of Cu-Zr and Ni-Zr metallic glasses have been studied by neutron diffraction and Reverse Monte Carlo (RMC) modeling. A pre-peak at Q similar to 17 nm(-1) was observed in the structure factor, S(Q), of Ni-Zr metallic glasses, and this is associated with the Ni-Ni partial structure factor was well reproduced by the RMC modeling. An analysis of Voronoi polyhedra in the RMC simulations was used to characterise the different atomic configurations around Zr, Ni and Cu atoms. The Zr environments are very similar in the two systems, but there are marked differences between the polyhedra around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by trigonal prismatic-like, Archimedian antiprismatic-like, and similar polyhedra, with smaller total coordination numbers less than 10. In contrast, icosahedron-like polyhedra with total coordination numbers in excess of 1 I are preferred for Cu. (c) 2006 Elsevier Ltd. All rights reserved.

The nanocrystallization process in amorphous Fe84Nb7B9 alloy was studied by means of energy-filtering transmission electron microscopy. Energy-filtered diffraction intensity provided quantitative structural analysis for the as-quenched state with the help of reverse Monte Carlo simulation. Using the Fe L-edge it was found from chemical mapping that chemical segregation of Fe with Fe-rich and Fe-poor regions starts to occur at the later stage of nanocrystallization. (c) 2006 Springer Science + Business Media, Inc.

The local structure in a Pd40 Ni40 P20 bulk metallic glass was examined using a spherical-aberration-corrected high resolution TEM. Fcc-Pd(Ni) type nanoclusters and local compound (phosphide)-like nanoclusters with sizes of 1-2 nm embedded in a dense-randomly-packed amorphous matrix were clearly observed under an appropriate imaging condition. However, three-dimensional atom-probe elemental mapping revealed there is virtually no nanoscale compositional difference between the nanoclusters and amorphous matrix beyond the statistical error range. A very small interfacial energy between the nanophase and the matrix is able to form a metastable amorphous phase with a structural fluctuation. © 2006 The American Physical Society.

Changes in crystallographic features during the (bcc→bcc+C14 structure) reaction have been investigated for Fe-Mo alloys containing around 10 at. % Mo by transmission electron microscopy. The metastable bcc Fe-Mo alloys were annealed at the relatively low temperature of 1023 K in order to elucidate the details of the structural change in the initial stage. The annealing led to the appearance of precipitates in the bcc matrix, which did not have the C14 structure even after 1000 h of annealing. The structure of the precipitate was basically characterized by a disordered arrangement of distorted decagonal columns. The column was composed of distorted icosahedral clusters connected one-dimensionally. In addition, annealing was found to cause an increase in the number of C14 configurations for the local arrangement of these decagonal columns.

Changes in crystallographic features during the (bcc--&gt;bcc+C14 structure) reaction have been investigated for Fe-Mo alloys containing around 10 at. % Mo by transmission electron microscopy. The metastable bcc Fe-Mo alloys were annealed at the relatively low temperature of 1023 K in order to elucidate the details of the structural change in the initial stage. The annealing led to the appearance of precipitates in the bcc matrix, which did not have the C14 structure even after 1000 h of annealing. The structure of the precipitate was basically characterized by a disordered arrangement of distorted decagonal columns. The column was composed of distorted icosahedral clusters connected one-dimensionally. In addition, annealing was found to cause an increase in the number of C14 configurations for the local arrangement of these decagonal columns.

In the Ni3Al0.52V0.48 alloy, D0(22) precipitation in the supersaturated L1(2) matrix has been found to stagnate due to the occurrence of the L1(2)--&gt;L1(2)+D0(22)--&gt;L1(2) structural change in an isothermal process. In this paper, we experimentally show the variation of the L1(2) and D0(22) chemical compositions during the structural change. Our results reveal that the transient D0(22) formation accompanies a large concentration fluctuation, while the final L1(2) composition reverts back to the initial L1(2) one. It is also found that the average V content of the D0(22) regions decreases together with the change in the L1(2)/D0(22) habit planes from the {100} to {110} ones. These experimental results are indicative of the suppression of atomic diffusion and subsequent redistribution of Al and V in the L1(2) matrix, resulting in D0(22) annihilation. It is proposed that jump site selectivity and cooperative atomic migration in the L1(2) structure are important factors in the suppression of atomic diffusion. Because the appearance of these factors correlates well with the vacancy concentration of the L1(2) matrix, it is concluded that the stagnation of D0(22) precipitation represents one kinetic process under the present thermodynamic path.

The Cu2Mg-type structure, called the C15 structure, is one of the covalency-involved structures in alloys and is characterized by a three-dimensional network of the covalent tetrahedra of small majority atoms. In order to understand the formation of covalent bonds in alloys, the crystallographic features of the C15 structure in the (bcc--&gt;hcp+C15) reaction of the Ti-(30- and 40-at. %) Cr alloys have been examined by transmission electron microscopy. It was found that the C15 structure was formed from the metallic bcc structure via the formation of icosahedral atomic clusters. Based on the shape of the icosahedral cluster, the cluster should be produced as a result of the local formation of covalent bonds along one of the &lt;110&gt;(B) directions. It can thus be said that, in relation to the formation of the covalency-involved C15 structure from the metallic bcc structures, the local covalent bonds between two Cr atoms are first formed in the bcc matrix, and then that the local bonds are developed into the three-dimensional network of the covalent tetrahedra consisting of four Cr atoms.

The new chemical layered structure, referred to as a chemical stripe structure, was found as a metastable state in the (bcc--&gt;hcp + C15) metastable phase separation in the Ti-Cr alloys. Note that a metastable separation is here defined as a separation characterized by a positive value of the second derivative of Gibbs free energy with respect to chemical composition. The experimental data showed that the layered structure had periodicity of 4 x d(002), about 0.72 nm, and chemical ordering of Ti : Cr = 3 : 1, and that a lot of antiphase boundaries with phase shifts of pi/2 and pi were involved in the structure. The coherent length of the layered structure was estimated to be about 15 nm along the modulated direction. In addition to these features, it was found that the layered structure was formed from the local bct state as another metastable state, not directly from the zone structure consisting of one Cr layer. On the basis of these data, the physical origin of the formation of the chemical layered structure is also discussed.

The crystallographic features of a bcc --&gt; hcp + C15 structural change in a Ti-30 mol%Cr alloy have been examined by transmission electron microscopy. When the alloy was annealed at 873 K below the eutectoid temperature, the structural change occurred in the following five steps: bcc --&gt; bcc + Zone I --&gt; bcc + Zone II --&gt; bcc + Zone II + hcp --&gt; bcc + hcp + C15 --&gt; hcp + C15. The interesting features of the change are that the diffuse omega state is present in the metastable bee matrix, and that in the fourth step the C 15 grains with a size of about 2 nm appear in the bee matrix around the hcp region. As a result of these extremely small C 15 grains, the final microstructure, which was obtained from the 5-h-and 100-h-annealed samples, consists of the hcp and C15 grains with an average size of about 100 nm. On the basis of these results, the physical origin of the nm-size polycrystallization in the appearance of the C15 phase is discussed in relation to both the presence of diffuse omega state in the metastable bcc matrix and the formation of the complex coordinated polyhedra in the C15 structure.