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Nitrate, a common pollutant in water, can be used as a nitrogen source for electrocatalytic ammonia production. Bismuth oxide (Bi2O3) is a promising electrocatalyst because of earth‐abundance and high hydrogen overpotential. However, it also has the disadvantages of easy agglomeration and poor charge transfer. This study demonstrated that the high dispersion of Bi2O3 nanosheets can be achieved through in‐situ growth on Ti3C2Tx MXene nanosheets that improved the efficiency of charge transmission, and thus improving the electrocatalytic ammonia production performance. A NH3 yield rate of ∼7.00 mg h−1 cm−2 with faradic efficiency of 91.1 % could be achieved on 11 % Bi2O3/MXene. Density functional theory (DFT) calculations, electrochemical active surface area (ECSA) and electrochemical impedance spectroscopy (EIS) proved that the excellent ammonia production performance came from the fact that bismuth oxide itself could inhibit hydrogen evolution, and in situ growth on MXene enabled high active site exposure and enhanced charge transfer capacity. [ABSTRACT FROM AUTHOR]

A new bistable shell with two symmetric configurations is proposed by using the nanotechnology, surface mechanical attrition treatment (SMAT), to locally treat a rectangular region. The impacts from randomly fast moving balls during the process induce nanotwins and mesh material grains into nanoscale on originally flat plates, which largely increase the material's yield strength and elastic deformation capacity. Also, the plastic deformations accumulated from thousands of impacts may stretch the plate under the constraint from the untreated region, while inducing internal compressive forces in the processed region. The experiments show that, when the accumulated plastic deformations are large enough, the locally nanostructured plate may buckle transversely by the internal forces to hold two different stable configurations, resulting in the bistable feature. An analytical model is developed to predict the stable configurations, which is numerically verified and experimentally validated. The parameters, including the SMAT region, plate dimensions, and SMAT process, to design the stable configurations of the bistable shells are systematically studied experimentally, analytically, and numerically. [ABSTRACT FROM AUTHOR]

Pulsed laser ablation in liquid (PLAL) is gradually becoming an attractive approach for nanomaterial fabrication because it is a chemically simple and clean method with high product purity. We studied the laser interaction with bulk target and particle products in detail, including mechanism process, target morphology and nanoparticle products. We captured three oscillations of one bubble after laser ablates the bulk target and calculated the variation of pressure and temperature inside the bubble. The results show that the first bubble oscillation has greatest impact on the nanomaterial synthesis, and the most powerful stages for the material synthesis during all the bubble oscillations are the beginning of each expansions and the end of each shrinks. Nanomaterial releases from the bubble at the end of each oscillations. In addition, based on the analysis of ablation cavity on the target, it is found that the cavity depth increases with the number of laser pulses, and then the depth tends to be under saturation status, which means it is difficult to obtain great improvement of the nanomaterial productivity just by prolonging the laser irradiation time. More importantly, the strong interaction between laser and particle products is presented clearly by time-resolved shadowgraphy, which can contributed to the modification of nanoparticle products. [ABSTRACT FROM AUTHOR]

Lead (Pb) is one of the impurities that cause stress corrosion cracking (SCC) of the tubing material in the steam generator (SG), the corrosion behavior of surface mechanical attrition treatment (SMAT) treated surface was measured for alloy 690 in simulated SG condition with and without Pb contamination. Even though the polarization curves indicated the corrosion potential of SMAT-processed specimens shifted negatively, the positive effect of SMAT on resistance of SCC was observed. The reduced susceptibility to lead-induced stress corrosion cracking may be attributed to the formation of stable passive film and the significant compressive stress on the surface induced by SMAT. Impact Statement A significant compressive stress induced by the SMAT process effectively reduced the susceptibility of the alloys to lead-induced stress corrosion cracking. [ABSTRACT FROM AUTHOR]

The self-assembly of peptides and proteins under well-controlled conditions underlies important nanostructuring processes that could be harnessed in practical applications. Herein, the synthesis of a new hairpin peptide containing four histidine residues is reported and the self-assembly process mediated by metal ions is explored. The work involves the combined use of circular dichroism, NMR spectroscopy, UV/Vis spectroscopy, AFM, and TEM to follow the structural and morphological details of the metal-coordination-mediated folding and self-assembly of the peptide. The results indicate that by forming a tetragonal coordination geometry with four histidine residues, copper(II) ions selectively trigger the peptide to fold and then self-assemble into nanofibrils. Furthermore, the copper(II)-bound nanofibrils template the synthesis of CuS nanowires, which display a near-infrared laser-induced thermal effect. [ABSTRACT FROM AUTHOR]

We theoretically investigate the electron transport properties in a non-magnetic nanostructure with spin–orbit interactions and the δ -doping which can be experimentally realized by using metal-organic chemical-vapor deposition or molecular beam epitaxy. We find that the electron transmission and the spin polarization strongly depend not only on the height and the width of the barrier but also on the weight and the position of the δ -doping. These interesting phenomena may be very helpful for understanding the electron transport mechanism in a non-magnetic nanostructure and designing the δ -doping-tunable spintronic device based on the non-magnetic heterostructure. [ABSTRACT FROM AUTHOR]

Highlights: [•] Integrate high-strength nano-materials into lightweight design. [•] Lightweight design scheme for wind turbine tower application. [•] Expand the bending formulae for tapered tubular structures with varying thickness. [•] We rewrite the Secant Formula for a tapered beam under eccentric compression. [Copyright &y& Elsevier]

Hydrogels resulting from the self-assembly of small peptides are smart nanobiomaterials as their nanostructuring can be readily tuned by environmental stimuli such as pH, ionic strength and temperature, thereby favoring their practical applications. This work reports experimental observations of formation of peptide hydrogels in response to the redox environment. Ac-IK-NH is a short peptide amphiphile that readily self-assembles into long nanofibers and its gel formation occurs at concentrations of about 10 mmol/L. Introduction of a Cys residue into the hydrophilic region leads to a new molecule, Ac-ICGK-NH, that enables the formation of disulfide bonds between self-assembled nanofibers, thus favoring cross-linking and promoting hydrogel formation. Under oxidative environment, Ac-ICGK-NH formed hydrogels at much lower concentrations (even at 0.5 mmol/L). Furthermore, the strength of the hydrogels could be easily tuned by switching between oxidative and reductive conditions and time. However, AFM, TEM, and CD measurements revealed little morphological and structural changes at molecular and nano dimensions, showing no apparent influence arising from the disulfide bond formation. [ABSTRACT FROM AUTHOR]

Abstract: Rendering a bimodal grain size distribution in nanostructured materials has been proved to effectively achieve both higher strength and higher ductility, which is based on the ansatz that large grains provide hardening ability and small grains provide larger yield stress. Here we propose a theoretical model focusing on the behaviour of nano/microcracks, which nucleate in the nano/ultrafine grained phase and stop at the boundary of large grains during the plastic deformation. We found that nano/microcracks do not lead to catastrophic failure; instead, they induce the back stress for the strain hardening and also the variation of the mechanical behaviour in the nano/ultrafine grained phase. With the aid of the modified mean field approach, the stress–strain relationship of the bimodal metals can be derived by combining the constitutive relations of the nano/ultrafine grained phase and the coarse grained phase. Numerical results show that the proposed model can successfully describe the enhanced strength and ductility of the bimodal metals. The predictions of the bimodal nickels are in good agreement with the experimental results. It is further noted that the strength and ductility of a bimodal metal are sensitive to the volume fraction of constituents and the distribution of nano/microcracks. This theoretical model can be utilized to optimize the mechanical properties of the bimodal metals, by tuning the constituent fractions and the size of the microstructures. [Copyright &y& Elsevier]

Abstract: We systematically model the hydrogen adsorption in nanoporous carbons over a wide range of carbon bulk densities (0.6–2.4g/cm3) by using tight binding molecular dynamics simulations for the carbon structures and thermodynamics calculations of the hydrogen adsorption. The resulting structures are in good agreement with the experimental data of ultra-microporous carbon (UMC), a wood-based activated carbon, as indicated by comparisons of the microstructure at atomic level, pair distribution function, and pore size distribution. The hydrogen adsorption calculations in carbon structures demonstrate both a promising hydrogen storage capacity (excess uptake of 1.33wt.% at 298K and 5MPa, for carbon structures at the lower range of densities) and a reasonable heat of adsorption (12–22kJ/mol). This work demonstrates that increasing the heat of adsorption does not necessarily increase the hydrogen uptake. In fact, the available adsorption volume is as important as the isosteric heat of adsorption for hydrogen storage in nanoporous carbons. [Copyright &y& Elsevier]

Abstract: The spin-dependent electron transport is numerically studied in a nonmagnetic nanostructure in the presence of both Dresselhaus and Rashba spin-orbit interactions. It is shown that the large spin polarization can be achieved in such a structure mainly due to the Rashba spin-orbit term induced splitting of the resonant level. It is also shown that the spin polarization strongly depends on the well width and the thickness of the middle barrier as well as the height of the middle barrier. [Copyright &y& Elsevier]

Abstract: The giant magnetoresistance (MR) effect is theoretically studied in a magnetically modulated two-dimensional electron gas. We find that the significant transmission difference for electron tunneling through parallel and antiparallel magnetization configurations results in a considerable MR effect. We also find that the MR ratio strongly depends on the magnetic strength and the distance between the left edges of two ferromagnetic strips as well as the temperature. [Copyright &y& Elsevier]

Abstract: In this paper, we theoretically study the effect of the in-plane magnetic field on spin polarization in the presence of the Dresselhaus spin–orbit effect. It is shown that the large spin polarization can be achieved in such a nanostructure due to the effects of both the Dresselhaus spin–orbit term and the in-plane magnetic field, but the latter plays a main role in the tunneling process. It is also shown that with the increase of in-plane magnetic field, the degree of spin splitting obviously becomes larger. [Copyright &y& Elsevier]

Water-soluble thioglycolic acid-capped CdSe nanocrystals (NCs) were prepared in aqueous solution at room temperature. We investigated the effects of pH values on the fluorescence intensity of the as-prepared CdSe NCs, and discussed the influence of the initial pH values on the fluorescence property. Their mean diameter was estimated to be 1.9 nm depending on the initial pH values in the preparation, the photoluminescence quantum yield could reach as high as 1.9%, almost comparable to the CdSe NCs prepared by an organometallic route. Finally, the products were characterized by Fourier transform infrared spectrometry (FTIR), atomic force microscope (AFM) and X-ray powder diffraction (XRD). AFM image showed that the NCs were ball-shaped with good dispersibility. XRD analysis disclosed that the CdSe NCs were of cubic zinc-blended structure. [ABSTRACT FROM AUTHOR]

Abstract: We theoretically investigate the transmission probability and the electron conductance as well as the spin polarization in a magnetically modulated two-dimensional electron gas under the influence of the periodic . It is observed that these quantities sensitively depend on the number (m) of periods. For the number, , the spin splitting occurs in each resonant domain, and the number of the spin-splitting peaks in each resonant domain is 2m−1. It is also observed that the electron conductance decreases for the bigger m, and both the transmission probability and the spin polarization show a similar-periodic profile with the increase of L. [Copyright &y& Elsevier]

[Display omitted] • Ultrafast in-situ transformation of graphite into graphene nanosheets by HCPEB direct irradiation is developed for the first time. • Impurity-free graphene with thickness less than 10 layers reaches 95%. • The transformation mechanism is ascribed to the transient internal expansion of graphite. • The effective transformation is due to the equal thermal stress and deformation of adjacent layers in graphite. Environmental-friendly and efficient transformation of graphite to obtain impurity-free graphene remains challenging. Herein, a novel approach for in-situ transformation of graphite into graphene is proposed. The graphite particles were irradiated directly by high current pulsed electron beam (HCPEB) with pulse duration of 2 μs. The morphology and microstructure changes were characterized by Raman spectrum, X-ray diffraction, confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscope (AFM) methods. It is revealed that the surface layer on graphite particles of thickness ∼ 10 μm was transformed to graphene nanosheets effectively, where the content of graphene with thickness less than 10 atom layers reached 95%. The numerical simulation results showed that the heating temperature in the subsurface layer would be 3246 ℃ and the thermal stress amplitude ∼ 110 MPa, which leads to the instantaneous expansion and breakdown of interlayer combination and realizes the transformation of graphite into graphene microstructure. This study demonstrated the potential of using HCPEB for ultrafast in-situ transformation of graphite into graphene nanosheets. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we theoretically investigate the conductance and the magnetoresistance effect in a periodically magnetically modulated two-dimensional electron gas. It is shown that there exists a significant conductance difference for electrons through the parallel and antiparallel magnetization configurations, which leads to a considerable magnetoresistance effect. It is also shown that the conductance and the magnetoresistance effect depend on both the temperature and the number of the periodic magnetic barriers. [Copyright &y& Elsevier]

Abstract: The bias- and temperature-dependent magnetoresistance (MR) effect is theoretically investigated in a magnetically modulated nanostructure, which can be realized experimentally by depositing two parallel ferromagnetic strips on the top and bottom of a semiconductor heterostructure. It is found that a considerable MR effect can be achieved due to the quite distinct conductance difference for electrons through the parallel and antiparallel magnetization configurations. It is also found that the MR effect depends not only on the temperature, but also on the applied bias, thus may leading to bias- and temperature-tunable MR devices. [ABSTRACT FROM AUTHOR]

AISI 301 stainless steel (SS) is known for its high strength and hardness but tends to be less corrosion resistant for many applications. Several attempts have been made in the past to investigate its corrosion behavior by different methods. However, current knowledge is insufficient on its corrosion resistance when subjected to surface treatment. In this work, a new route to enhance the corrosion resistance of nanostructured 301 SS using surface mechanical attrition treatment (SMAT) method is described. SMAT improves the mechanical properties of 301 SS by the formation of a nanostructure layer on the material surface. Compared to the as‐received 316 and 304 SS counterparts, the present nanostructured 301 SS exhibits an improved corrosion behavior by a lower corrosion current density (1.308 mA/cm2), higher corrosion potential (−0.071 V), higher phase angle and impedance, better charge‐transfer resistance, and Cr content. The improved corrosion resistance can be attributed to the ability of SMAT to facilitate the move of Cr on the surface, which forms a stronger passivation layer with a new mechanism of passivation that may save a lot of noble metals. [ABSTRACT FROM AUTHOR]

Highlights • Bistable metallic disks are manufactured by nanostructuring disks in a localized region. • Refined analytical models characterizing bistable behaviors are proposed. • Six transition types are found for bistable disks with different nanostructured regions. • Bistable metallic disks have good stabilities indicated by snapping forces. Abstract In contrast to conventional bistable disks manufactured using soft materials in spherical or domelike configurations, new bistable disks with designable configurations and high load-bearing capacities are proposed and developed based on the nanotechnology of surface mechanical attrition treatment (SMAT). A simple analytical model with explicit results, refined analytical models and numerical models are formulated to predict two stable configurations and study their transition processes. A simple algorithm that includes a confined equation for the formulated Ritz models is developed via a displacement control strategy to capture the full snapping processes of the bistable disks, which are actuated by a point force. The analytical models for the bistable disks identify various stable configurations and six transition strategies, and these are discussed systematically with respect to the design parameters. The ratio of the nanostructured region in the disks is found to have a critical influence on the stable configurations and the transition processes. The results from the experimentally manufactured bistable disks validate the obtained theoretical results. [ABSTRACT FROM AUTHOR]

Highlights • Two transition paths are found for the bistable disks under uniform forces. • Snapping forces required for transitions depend on actuated regions. • The transitions can be triggered by pneumatic actuation for automatic reconfiguration. Abstract An analytical model is formulated for transitions of locally nanostructured bistable disks triggered by distributed transverse forces under a displacement control strategy. Different transition paths are found for the bistable disks actuated by transverse forces applied to different regions, even though the input energy before snapping is the same. The analytical results show that the snapping force varies and is considerably affected by the distribution of the applied force, which is corroborated by numerical modelling. The analytical model is used to obtain the design parameters of bistable disks for which transition can be induced by distributed forces less than one atmospheric pressure. These parameters include the disk flakiness, the plastic deformation accumulated from nanocrystallisation and the percentage of the nanostructured regions of the disks. Transition tests of the manufactured bistable disks based on pneumatic actuations validate the developed analytical model. This study provides an applicable approach to automatically trigger transitions of bistable disks between two stable configurations, including a snapping-through process and a snapping-back process. [ABSTRACT FROM AUTHOR]

Abstract Two-dimensional metal organic framework nanosheets demonstrate various applications in chemical separation and purification, biological recognition and sensing, catalysis, and optoelectronics, though the exfoliation of metal organic framework nanosheets with good dispersibility are challenging. Here we report an efficient method for exfoliating a novel tellurophene-based two-dimensional metal organic framework with a branched polymer surfactant polyethylenimine ethoxylate to prepare single- and few-layer nanosheets. Furthermore, the hybrid ink is directly integrated as an electron extraction layer for high-performance organic solar cells, which exhibits enhanced power conversion efficiency in comparison to the polyethylenimine ethoxylate-based ones due to the suppressed charge recombination, tunable work function and improved conductivity. This contribution not only reports a novel method to prepare stable two-dimensional metal organic framework nanosheets but also opens an avenue for their applications in solar cells. Graphical abstract Image 1 Highlights • A novel layered metal organic framework based on tellurophene was synthesized. • The MOF bulk was exfoliated to single- and few-layer nanosheets with a surfactant. • The hybrid MOF-PEIE used as an EEL in OSCs showed superiority over PEIE. • The mechanism of enhancement of MOF-PEIE based OSCs was fully investigated. [ABSTRACT FROM AUTHOR]

Surface mechanical attrition treatment (SMAT) is a powerful and practical method to surface-harden metals and alloys through the generation of a gradient nanostructured surface. In this study 304 stainless steel was SMAT processed and the mechanical response upon repeated frictional sliding is studied as well as compared to the mechanical response of untreated as-received 304 stainless steel. The repeated frictional sliding experimental work is complemented by finite-element analysis in order to quantify the stress and strain distribution and to qualitatively determine the elastic-plastic deformation behavior. It is shown that repeated frictional sliding on the SMAT processed 304 stainless steel surface results in smaller residual depth, pile-up height and friction coefficient but higher maximum stresses compared to the as-received 304 stainless steel. After approximately 30 cycles the residual depth increases only minimally with each additional cycle because of strain hardening and increased contact area. At low cycle numbers the frictional sliding track of the as-received 304 stainless steel meanders and forms slip bands adjacent to the sliding track. Due to instability of the gradient structure of 304 SMAT processed stainless steel, asperities are formed in the inner zone of sliding tracks at increasing cycle numbers. [ABSTRACT FROM AUTHOR]

Abstract: In recent years, the micro- and nanoscale structures and materials are observed and characterized under microscopes with large magnification at the cost of small view field. In this paper, a new phase-shifting inverse geometry moiré method for the full-field reconstruction of micro- and nanoscale planar periodic structures is proposed. The random phase shift techniques are realized under the scanning types of microscopes. A simulation test and a practical verification experiment were performed, which demonstrate this method is feasible. As an application, the method was used to reconstruct the structure of a butterfly wing and a holographic grating. The results verify the reconstruction process is convenient. When being compared with the direct measurement method using point-by-point way, the method is very effective with a large view field. This method can be extended to reconstruct other planar periodic microstructures and to locate the defects in material possessing the regular lattice structure. Furthermore, it can be applied to evaluate the quality of micro- and nanoscale planar periodic structures under various high-power scanning microscopes. [ABSTRACT FROM AUTHOR]

The dynamic plastic behavior related to the gradient distribution of twin spacing in 304 stainless steel thin wires is investigated experimentally with the strain rate varying from 1 × 10 − 3 /s to 1.5 × 10 4 /s. Such gradient-nanotwinned structures are prepared by surface mechanical attrition treatment. A mechanism-based dynamic plastic model is developed to describe the strain-rate dependent stress-strain response in gradient-nanotwinned austenite stainless steels. A good agreement between experimental data and simulations was achieved, and further theoretical predictions demonstrated that the dynamic plastic behavior is sensitive to the twin spacing and volume fraction of gradient-nanotwinned region in austenite stainless steel wires. [ABSTRACT FROM AUTHOR]

Austenite stainless steels with gradient nanostructure exhibit exceptional combination of high yield strength and high ductility. In order to describe their structure-property relation, a theoretical model is proposed in this work, in which the depth-dependent bimodal grain size distribution and nanotwin-nanograin composite structure are taken into account. The micromechanical model and the Voigt rule of mixture are adopted in deriving the constitutive relations. Furthermore, the evolution and influence of the nano/micro cracks/voids are considered for predicting the failure strain. The numerical results based on the theoretical model agree well with experimental results in terms of the yield strength, ductility, and the strain hardening rate, demonstrating that the proposed model can well describe the mechanical properties of gradient-nanostructured austenite stainless steels. We further study the variations of the yield strength and ductility of gradient-nanograined and gradient-nanotwinned 304 stainless steels with different distribution of grain size and twin spacing along the depth, which shows that the present model can be applied to optimize the combination of strength and ductility of the gradient-nanostructured metals by tuning depth-dependent distributions of microstructures. [ABSTRACT FROM AUTHOR]

Surface mechanical attrition treatments (SMATs) were used to prepare nanostructured surface layers on alloys used in nuclear power plant steam generators (SGs). The effects of surface nanocrystallization on alloy corrosion behavior at room temperature and at 300 °C in a simulated SG environment were studied. At room temperature, the polarization curves indicated that with increasing SMAT duration, the corrosion potential of the samples shifted negatively from smaller to larger values, and alloy active dissolution rate and passive current density both increased. Nitriding treatment was used to improve the corrosion resistance. Compared with corrosion behavior observed at room temperature, corrosion resistance in the simulated SG condition was highly enhanced because the nano-sized-grain layer formed via SMAT provided a higher density of nucleation sites for the formation of a passive film and diffusion paths for Cr, leading to the rapid formation of a dense protective oxide layer. [ABSTRACT FROM AUTHOR]

Bacillus-shaped bilayer vesicles of nanoscale size are very rare structures of stable surfactant self-assembly, because they are both thermodynamically and electrostatically unfavorable in solution. It is evidently demonstrated that appropriately aqueous mixtures of single-tailed cationic and anionic (catanionic) surfactants can produce rigidly bacillus-shaped bilayer vesicles with both flat parts and bent edges. The crucial requirement for forming bacillus-shaped bilayer vesicles is the use of cationic surfactants with relatively hydrophobic [FeCl3Br]− as counterions. [FeCl3Br]− can strongly associate with cationic surfactants to partition into the hydrophobic bilayer of bacillus-shaped bilayer vesicles, significantly increasing the edge energy of cationic surfactants to make them distribute in the low curvature part of bilayers. This causes the formation of bacillus-shaped bilayer vesicles, but not completely bent spherical vesicles, in the case of cationic surfactant excess. The specificity of hydrophobic counterions, [FeCl3Br]−, could also make the catanionic mixtures do not precipitate at the stoichiometric point. This new self-assembly on catanionic systems is culminated in the discovery of beautifully structured colloidal objects which are of practical use for molecular templating and controlled drug or DNA release. [ABSTRACT FROM AUTHOR]

To understand how molecular interactions lead to the self-assembly of twisted, helical and flat nanoribbons, we have compared the hierarchical self-assembly processes of three selected octapeptides with the same amino acid composition but different sequences by both experiments and molecular dynamics (MD) simulations. KE-F8 (NH 2 -KEFFFFKE-CONH 2 ) and EK-F8 (NH 2 -KEFFFFEK-CONH 2 ) have the same distribution of hydrophobic residues and only differ by swapping the positive and negative charged residues at their C-terminals, while KFE-8 (NH 2 -KFEFKFEF-CONH 2 ) differs from KE-F8 and EK-F8 by having all hydrophobic and charged residues evenly distributed. MD simulations indicated that the competition between electrostatic and hydrophobic interactions at the molecular level results in different initial packing modes: KE-F8 monomers form completely matched anti-parallel β -sheets, EK-F8 monomers align with one residue shifting, and KFE-8 monomers pack β -sheets with two heterogeneous surfaces, consistent with previously suggested models. Driven by inter-strand and inter-sheet interactions, further growth of these molecular templates leads to larger oligomers with different twisting and stacking degrees, which are structurally consistent with the experimentally observed self-assembled morphologies. Further MD simulations showed that the competition between intra- β -sheet and inter- β -sheet interactions is responsible for the different twisting and stacking degrees of β -sheets and the subsequent formation of different nanostructures (twisted ribbons for KE-F8, helical ribbons/tubes for EK-F8 and flat ribbons for KFE-8). This study thus provided an important mechanistic insight into the fine tuning of molecular packing and interactions via peptide sequence variation leading to controllable self-assembly of twisted, helical and flat nanostructures. [ABSTRACT FROM AUTHOR]

Diamonds have substantial hardness and durability, but attempting to deform diamonds usually results in brittle fracture. We demonstrate ultralarge, fully reversible elastic deformation of nanoscale (~300 nanometers) single-crystalline and polycrystalline diamond needles. For single-crystalline diamond, the maximum tensile strains (up to 9%) approached the theoretical elastic limit, and the corresponding maximum tensile stress reached ~89 to 98 gigapascals. After combining systematic computational simulations and characterization of pre- and postdeformation structural features, we ascribe the concurrent high strength and large elastic strain to the paucity of defects in the small-volume diamond nanoneedles and to the relatively smooth surfaces compared with those of microscale and larger specimens. The discovery offers the potential for new applications through optimized design of diamond nanostructure, geometry, elastic strains, and physical properties. [ABSTRACT FROM AUTHOR]

Peptide self-assembly is of directrelevance to protein scienceand bionanotechnology, but the underlying mechanism is still poorlyunderstood. Here, we demonstrate the distinct roles of the noncovalentinteractions and their impact on nanostructural templating using carefullydesigned hexapeptides, I2K2I2, I4K2, and KI4K. These simple variationsin sequence led to drastic changes in final self-assembled structures.β-sheet hydrogen bonding was found to favor the formation ofone-dimensional nanostructures, such as nanofibrils from I4K2and nanotubes from KI4K, but the lack ofevident β-sheet hydrogen bonding in the case of I2K2I2led to no nanostructure formed. The lateralstacking and twisting of the β-sheets were well-linked to thehydrophobic and electrostatic interactions between amino acid sidechains and their interplay. For I4K2, the electrostaticrepulsion acted to reduce the hydrophobic attraction between β-sheets,leading to their limited lateral stacking and more twisting, and finalfibrillar structures; in contrast, the repulsive force had littleinfluence in the case of KI4K, resulting in wide ribbonsthat eventually developed into nanotubes. The fibrillar and tubularfeatures were demonstrated by a combination of cryogenic transmissionelectron microscopy (cryo-TEM), negative-stain transmission electronmicroscopy (TEM), and small-angle neutron scattering (SANS). SANSalso provided structural information at shorter scale lengths. Allatom molecular dynamics (MD) simulations were used to suggest possiblemolecular arrangements within the β-sheets at the very earlystage of self-assembly. [ABSTRACT FROM AUTHOR]

Abstract: A statistical analysis is employed to investigate the mechanical performance of nanostructured metals with bimodal grain size distribution. The contributions of microcracks in the plastic deformation are accounted for in the mechanism-based plastic model used to describe the strength and ductility of the bimodal metals. The strain-based Weibull probability distribution function and percolation analysis of microcracked solids are applied to predict the failure behavior of the bimodal metals. The numerical results show that the proposed model can describe the mechanical properties of the bimodal metals, including yield strength, strain hardening and uniform elongation. These predictions agree well with the experimental results. The stochastic approaches adopted in the proposed model successfully capture the failure behavior of bimodal coppers that are sensitive to grain size and the volume fraction of coarse grains in addition to the corresponding threshold for percolation. These results will benefit the optimization of both strength and ductility by controlling constituent fractions and the size of the microstructures in materials. [Copyright &y& Elsevier]

Abstract: We have developed a mechanism-based plasticity model of nanotwinned metals to investigate the effect of twin spacing on strength, ductility and work hardening rate of such materials. In particular, the unique roles of dislocation pile-up zones near twin and grain boundaries, as well as twinning partial dislocations, in strengthening and work hardening are incorporated in the model. Competition between different local failure mechanisms associated with twin lamellae and/or grain boundaries is considered in evaluating the tensile ductility of nanotwinned metals. The present study provides a quantitative continuum plasticity model capable of describing the variations in strength, ductility and work hardening rate of nanotwinned metals with the twin spacing. For nanotwinned copper a grain size of 500nm, the model predicts a critical twin spacing for the maximum strength at 13nm, in excellent agreement with experimental observations. The critical twin spacing is found to be linearly proportional to the grain size, which is consistent with recent molecular dynamics simulations. [Copyright &y& Elsevier]

Abstract: A granular structure is usually modeled by a parallelepiped containing spherical balls in three dimensions or by a rectangle filled with disks in two dimensions. These grains (spherical balls or disks) are disjoint and their size correspond to a size distribution determined by experiments. In this paper, we consider the geometrical modeling and the meshing of these structures. To define the repartition of disjoint grains, we propose a new constructive algorithm based on an advancing-front approach. Often, the use of an advancing-front algorithm leads to a heterogeneity of the local density in the generated structure. In order to homogenize this density, we propose an optimization method based on local grain relocations. Furthermore, we introduce a method to transform spherical balls into polyhedral cells similar to realistic grain shapes. To generate quality meshes of granular models with, either spherical balls (disks) or polyhedral (polygonal) cells, an adaptive scheme is proposed. The mesh generation method is a combined advancing front-Delaunay approach governed by a metric field. The metric specification is based on the geometry and the proximity of grains. [Copyright &y& Elsevier]

A new method for manufacturing nanomaterials with high ductility on a large scale is reported here. Based on surface nanocrystallization and warm co-rolling technologies, the resulting material amazingly exhibits high strength and exceptional ductility. Stainless steel was selected to demonstrate the extensibility of our approach. The yield strength (878MPa) is more than double that of the monolithic material. The elongation to failure (48%) triples comparing with the material with the same yield strength obtained by work hardening. [Copyright &y& Elsevier]

Abstract: A novel polyimide (PI) hybrid nanocomposite containing polyhedral oligomeric silsesquioxane (POSS) with well defined architecture has been prepared by copolymerization of octakis(glycidyldimethylsiloxy)octasilsesquioxane (Epoxy–POSS), 4,4′-oxydianiline diamine (ODA), and 4,4′-carbonyldiphthalic anhydride (BTDA). In these nanocomposite materials, the equivalent ratio of the Epoxy–POSS and ODA are adjustable, and the resultant PI–POSS nanocomposites give variable thermal and mechanical properties. More importantly, we intend to explore the possibility of incorporating POSS moiety through the Epoxy–POSS into the polyimide network to achieve the polyimide hybrid with lower dielectric constant (low-k) and thermal expansion. The lowest dielectric constant achieved of the POSS/PI material (PI-10P) is 2.65 by incorporating 10wt% Epoxy–POSS (pure PI, k=3.22). In addition, when contents of the POSS in the hybrids are 0, 3, 10wt% (PI-0P, PI-3P, PI-10P), and the resultant thermal expansion coefficients (TEC) are 66.23, 63.28, and 58.25ppm/°C, respectively. The reduction in the dielectric constants and the resultant thermal expansion coefficients of the PI–POSS hybrids can be explained in terms of creating silsesquioxane cores of the POSS and the free volume increase by the presence of the POSS–tethers network resulting in a loose PI structure. [Copyright &y& Elsevier]

Nano-dual-phase glass-crystal (NDPGC) metallic materials as the novel nanostructured materials have been proved experimentally to possess excellent mechanical properties, e.g. the nearly ideal strength. The present work is concerned with the constitutive analysis of size-dependent deformation behaviors in micropillars of a NDPGC alloy based on the micromechanics approach. The mechanism-based constitutive models are developed to explore the sample-size dependent mechanical behaviors of NDPGC pillars. An energy-based criterion for shear-band nucleation is employed to predict the diameter-dependent number of shear bands in large micropillars subjected to compression. The flow activation in metallic glass, grain reorganization, and grain refinement are involved in the proposed constitutive model for small micropillars. Numerical results demonstrate that the proposed theoretical model can describe the constitutive behaviors of the Mg-based NDPGC alloy. Good agreements between the theoretical and experimental results are achieved for the stress-strain relations and the diameter-dependent number of shear bands in large micropillars. It is found that the critical pillar diameter for generating shear bands increases with grain size and that the yield strength of NDPGC micropillars increases with the reduction in grain size (from 50 to 10 nm) without causing the inverse Hall-Petch effect. Therefore, a good combination of high yield strength and excellent plasticity can be achieved with small micropillars under compression. These findings show that the proposed model can be applied to optimize the mechanical performance of NDPGC alloys by controlling the microstructural size and sample (or feature) size. • The constitutive models are developed to describe the mechanical performance of nano-dual phase glass-crystal alloys. • The energy-based criterion for generating shear bands is proposed to predict the transition of deformation mechanisms. • The metallic glass flow activation, grain reorganization and the grain refinement are considered in constitutive models. • The size-dependent mechanical properties in nano-dual phase glass-crystal alloy pillars are forecasted. • This study can optimize mechanical properties of nano-dual phase glass-crystal alloys by tuning microstructural size. [ABSTRACT FROM AUTHOR]

Hollow nanostructured materials are attractive in material science for both fundamental research and practical applications. In this study, anodization demonstrates its convenience and effectiveness for constructing elaborate hollow nanospheres, based on an interesting synthetic mechanism involving bubble-assisted anodic self-assembly. The thus fabricated hierarchical FeS/FeO x hollow nanospheres are directly grown on the Fe substrate, providing a novel type of binder-free anode for high-performance batteries. For instance, when applied in sodium ion batteries, the air-annealed anode delivers high capacity and stability, retaining 464.8 mA h g−1 after 100 cycles at 100 mA g−1. A simple, scalable, and cost-effective anodization method was developed to construct hierarchical FeS/FeO x hollow nanospheres on Fe substrate. Image 1 • A scalable one-step anodization method is used to obtain hollow nanospheres. • Hierarchical FeS/FeO x hollow nanospheres are directly self-grown on the substrate. • Bubble-assisted self-assembly mechanism is proposed during anodization. • Binder-free FeS/FeO x anode delivers a high performance for Na-ion storage. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the microstructure and texture evolution in pulsed electro-deposited copper samples and the additional effect of the Surface Mechanical Attrition Treatment (SMAT), which were analyzed by means of electron backscattering and X-ray diffractions. A transition in the microstructure was observed as the thickness of the deposit increased: from randomly oriented equiaxed (3D) nanograins at the beginning of the deposition process towards elongated (2D) nanograins having a strong 〈110〉 fibre texture. Meanwhile, the SMAT treatment is shown to randomize the strong texture of the electrodeposits. [ABSTRACT FROM AUTHOR]