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Large-scale production of vertically aligned single-walled carbon nanotubes (VA-SWCNTs) on metal foils promises to enable technological advancements in many fields, from functional composites to energy storage to thermal interfaces. In this work, we demonstrate growth of high-quality (G/D6, average diameters ∼ 2-3 nm, densities10

Graphic illustrating the chemical reactions that occur during sintering of LLZTO pellets up to 1100 °C.

A quantitative understanding of particle rigid body (RB) motion that inherently accompanies grain boundary (GB) diffusion is highly desirable to understand and control the dynamic interplay between coarsening and densification during solid state sintering. By computer simulation using a multi-phase-field approach, we analyze systematically the roles played by each of these processes at different stages of the shrinkage of the internal pore in a three-particle green body as a function of particle size as well as thermodynamic and kinetic factors of interfaces. We demonstrate that particle RB translation promotes both neck growth, and pore rounding and shrinkage. Moreover, the forces acting at GBs and pulling neighboring particles towards one another dynamically evolve as particles fuse. In contrast, particle RB rotation has no contribution to pore shrinkage. The translational force acting on an individual particle varies with not only its size, but also the number and sizes of its neighboring particles.

Multi-functional membranes with high permeance and selectivity that can mimic nature's designs have tremendous industrial and bio-medical applications. Here, we report a novel concept of a 3D nanometer (nm)-thin membrane that can overcome the shortcomings of conventional membrane structures. Our 3D membrane is composed of two three-dimensionally interwoven channels that are separated by a continuous nm-thin amorphous TiO2 layer. This 3D architecture dramatically increases the surface area by 6000 times, coupled with an ultra-short diffusion distance through the 2–4 nm-thin selective layer that allows for ultrafast gas and water transport, ∼900 l m−2 h−1 bar−1. The 3D membrane also exhibits a very high ion rejection (R ∼ 100% for potassium ferricyanide) due to the combined size- and charge-based exclusion mechanisms. The combination of high ion rejection and ultrafast permeation makes our 3DM superior to the state-of-the-art high-flux membranes whose performances are limited by the flux-rejection tradeoff. Furthermore, its ultimate Li+ selectivity over polysulfide or gas can potentially solve major technical challenges in energy storage applications, such as lithium–sulfur or lithium–O2 batteries.

Porous materials with engineered stretching-dominated lattice designs, which offer attractive mechanical properties with ultra-light weight and large surface area for wide-ranging applications, have recently achieved near-ideal linear scaling between stiffness and density. Here, rather than optimizing the microlattice topology, we explore a different approach to strengthen low-density structural materials by designing tube-in-tube beam structures. We develop a process to transform fully dense, three-dimensional printed polymeric beams into graphitic carbon hollow tube-in-tube sandwich morphologies, where, similar to grass stems, the inner and outer tubes are connected through a network of struts. Compression tests and computational modelling show that this change in beam morphology dramatically slows down the decrease in stiffness with decreasing density. In situ pillar compression experiments further demonstrate large deformation recovery after 30–50% compression and high specific damping merit index. Our strutted tube-in-tube design opens up the space and realizes highly desirable high modulus–low density and high modulus–high damping material structures. A nanoscale tube-in-tube sandwich structure is generated by a two-step templating-pyrolysis process, which strengthens the log-pile carbon architecture and slows down the decrease of stiffness with decreasing density.

The tensile properties of additively manufactured (AM) metals and alloys are among the most important variables that impact the potential applications of these materials. Here we examine and report on the tensile properties of AM 316L stainless steels fabricated by the laser powder-bed-fusion (L-PBF) technique, via twelve sets of optimized laser processing parameters that produce materials with density >98.8 ± 0.10%. A heterogeneous microstructure is observed in all L-PBF samples, including microscopic features such as dislocations, cellular walls, elemental segregations, local misorientations, impurities, precipitates, and a large fraction of low-angle grain boundaries (2-10°, ∼40–60%). The derived average grain size defined by high-angle grain boundaries (>10°) is ∼30–50 μm. Tensile testing reveals a yield strength ranging from 552 to 635 MPa and a tensile-elongation-to-failure (TEF) of 0.09–0.42 for directly-printed samples, whereas these values are 592–690 MPa and 0.29–0.50 for samples machined from the as-built rectangular thin plates. In all samples, we observe a variation of tensile yield strength within ∼15% but not the TEF, suggesting marginal microstructural changes despite a wide range of laser processing parameters. The large scatter of TEF in directly-printed samples originates from the sensitivity of thin gauge geometry (∼2 mm2 cross-section area) to the built-in flaws. We measured a substantially higher strain rate sensitivity (m∼0.02–0.03) of L-PBF 316L compared to the coarse-grained counterparts (∼0.006), together with a small activation volume of ∼20–30b3 (where b is the Burgers vector of 316L). These deformation kinetics parameters suggest that the tensile plasticity of L-PBF 316L is controlled by a much finer microstructural length scale than the measured grain size, consistent with the high strength and juxtaposed nano- to macro-structures seen in these materials. Strategies to optimize the tensile properties of AM materials are discussed.

We demonstrate the synthesis of high-surface-area, low-density refractory aerogels. The monolithic hafnium boride (HfB2) and zirconium boride (ZrB2) aerogels are prepared via borothermal reduction ...

In laser powder bed fusion (LPBF), recovered unfused powder from the powder bed often degrades upon sequential processing through mechanisms like thermal oxidation and particle satelliting from ejected weld spatters and particle-laser interactions. Given the sensitivity of LPBF performance and build quality to powder properties, spent powder is generally discarded after a few build cycles, especially for materials that are sensitive towards surface oxidation. This increases feedstock material costs, as well as costs associated with machine downtime during powder replacement. Here, a new method to chemically reprocess spent LPBF metal powder is demonstrated under ambient conditions, using a heavily oxidised Cu powder feedstock recovered from prior LPBF processing as a model material. This is compared to an equivalent virgin Cu powder. The near-surface powder chemistry has been analysed, and it is shown that surface oxide layers present on spent Cu powder can be effectively reset after rapid reprocessing (from 5 to 20 min). Diffuse reflectance changes on etching, reducing for gas-atomised virgin Cu powder due to the formation of anisotropic etch facets, and increasing for heavily oxidised spent Cu as the highly absorptive oxide layers are removed. The mechanism of powder degradation for moisture sensitive materials like Cu has been correlated to the degradation of LPBF deposits, which manifests as widespread and extensive porosity. This extensive porosity is largely eliminated after reprocessing the spent Cu powder. Chemically etched spent powder is therefore demonstrated as a practical feedstock in LPBF in which track density produced is comparable to virgin powder., Additive Manufacturing, 52, ISSN:2214-8604

Reed-Solomon tail-biting convolutional concatenated (RS-TBCC) codes are investigated in this paper, aiming to eliminate the rate loss caused by the tail bits of the traditional RS convolutional concatenated (RS-CC) codes. The iterative soft decoding (ISD) for the RS-TBCC code is proposed, which integrates the tail-biting maximum a posteriori (TB-MAP) decoding algorithm for the inner tail-biting convolutional (TBC) code and the adaptive belief propagation (ABP) decoding algorithm for the outer RS codes. The proposed decoding is able to obtain significant performance gains through iterations. The outer decoding output will be validated by the maximum likelihood (ML) criterion, which alters the feedback to the inner decoding. However, the effectiveness of ML assessment degrades as the outer codeword length decreases. Therefore, a modified ISD is also proposed for shorter RS-TBCC codes in which smaller RS codes are employed.

Porous materials with engineered stretching-dominated lattice designs, which offer attractive mechanical properties with ultra-light weight and large surface area for wide-ranging applications, have recently achieved near-ideal linear scaling between stiffness and density. Here, rather than optimizing the microlattice topology, we explore a different approach to strengthen low-density structural materials by designing tube-in-tube beam structures. We develop a process to transform fully dense, three-dimensional printed polymeric beams into graphitic carbon hollow tube-in-tube sandwich morphologies, where, similar to grass stems, the inner and outer tubes are connected through a network of struts. Compression tests and computational modelling show that this change in beam morphology dramatically slows down the decrease in stiffness with decreasing density. In situ pillar compression experiments further demonstrate large deformation recovery after 30-50% compression and high specific damping merit index. Our strutted tube-in-tube design opens up the space and realizes highly desirable high modulus-low density and high modulus-high damping material structures.

Safe, reliable materials with fast charging kinetics are required to increase the power density of batteries in electric vehicles. One potential avenue for improving kinetics involves disturbing th...

Gold is examined here as an alternative to copper for the selective dehydrogenation of ethanol to acetaldehyde and hydrogen. Despite its high selectivity, gold is only active at temperatures higher than 250 °C for this reaction. We demonstrate that addition of a small amount of Ni on either supported or unsupported Au surfaces induces resistance to sintering, along with a beneficial effect on the catalytic activity. NiAu alloys prepared here with Ni as the minority component to the limit of atomic dispersion in the gold surfaces, catalyze the reaction beginning below 150 °C. A significant decrease of the apparent activation energy from 96 ± 3 kJ/mol for the monometallic Au to 59 ± 5 kJ/mol for the alloy was found. The Ni dispersion and concentration as a function of gas environment was followed by in situ DRIFTS and by XPS. The stability of the catalyst morphology was investigated through post-reaction microscopy imaging and long-term stability tests under reaction conditions. As shown via dynamic reaction experiments, acetaldehyde and H2 were selectively produced up to 280 °C. A small drop of selectivity at higher temperatures is attributed to the formation of Ni clusters, as proven by CO-DRIFTS on the used sample. Comparison with samples of higher Ni loading, where Ni clusters are formed, clearly shows that they catalyze the undesired full decomposition of ethanol to CO, CH4, and H2.

Two-photon lithography (TPL) is a high-resolution additive manufacturing (AM) technique capable of producing arbitrarily complex three-dimensional (3D) microstructures with features 2-3 orders of magnitude finer than human hair. This process finds numerous applications as a direct route toward the fabrication of novel optical and mechanical metamaterials, miniaturized optics, microfluidics, biological scaffolds, and various other intricate 3D parts. As TPL matures, metrology and inspection become a crucial step in the manufacturing process to ensure that the geometric form of the end product meets design specifications. X-ray-based computed tomography (CT) is a nondestructive technique that can provide this inspection capability for the evaluation of complex internal 3D structure. However, polymeric photoresists commonly used for TPL, as well as other forms of stereolithography, poorly attenuate X-rays due to the low atomic number (Z) of their constituent elements and therefore appear relatively transparent during imaging. Here, we present the development of optically clear yet radiopaque photoresists for enhanced contrast under X-ray CT. We have synthesized iodinated acrylate monomers to formulate high-Z photoresist materials that are capable of forming 3D microstructures with sub-150 nm features. In addition, we have developed a formulation protocol to match the refractive index of the photoresists to the immersion medium of the objective lens so as to enable dip-in laser lithography, a direct laser writing technique for producing millimeter-tall structures. Our radiopaque photopolymer resists increase X-ray attenuation by a factor of more than 10 times without sacrificing the sub-150 nm feature resolution or the millimeter-scale part height. Thus, our resists can successfully replace existing photopolymers to generate AM parts that are suitable for inspection via X-ray CT. By providing the "feedstock" for radiopaque AM parts, our resist formulation is expected to play a critical role in enabling fabrication of functional polymer parts to tight design tolerances.

Many traditional approaches for strengthening steels typically come at the expense of useful ductility, a dilemma known as strength-ductility trade-off. New metallurgical processing might offer the possibility of overcoming this. Here we report that austenitic 316L stainless steels additively manufactured via a laser powder-bed-fusion technique exhibit a combination of yield strength and tensile ductility that surpasses that of conventional 316L steels. High strength is attributed to solidification-enabled cellular structures, low-angle grain boundaries, and dislocations formed during manufacturing, while high uniform elongation correlates to a steady and progressive work-hardening mechanism regulated by a hierarchically heterogeneous microstructure, with length scales spanning nearly six orders of magnitude. In addition, solute segregation along cellular walls and low-angle grain boundaries can enhance dislocation pinning and promote twinning. This work demonstrates the potential of additive manufacturing to create alloys with unique microstructures and high performance for structural applications.

The non-oxidative dehydrogenation of ethanol to acetaldehyde has long been considered as an important method to produce acetaldehyde and clean hydrogen gas. Although monometallic Cu nanoparticles have high activity in the non-oxidative dehydrogenation of ethanol, they quickly deactivate due to sintering of Cu. Herein, we show that adding a small amount of Ni (Ni0.01Cu − Ni0.001Cu) into Cu to form highly dilute NiCu alloys dramatically increases the catalytic activity and increases their long-term stability. The kinetic studies show that the apparent activation energy decreases from ∼70 kJ/mol over Cu to ∼45 kJ/mol over the dilute NiCu alloys. The improved performance is observed both for nanoparticles and nanoporous NiCu alloys. The improvement in the long-term stability of the catalysts is attributed to the stabilization of Cu against sintering. Our characterization data show that Ni is atomically dispersed in Cu. The comparison of the catalytic performance of highly dilute alloy nanoparticles with nanoporous materials is useful to guide the design of novel mesoporous catalyst architectures for selective dehydrogenation reactions.

3D nanoporous metals made by alloy corrosion have attracted much attention due to various promising applications ranging from catalysis and sensing to energy storage and actuation. In this work we report a new process for the fabrication of 3D open nanoporous metal networks that phenomenologically resembles the nano-Kirkendall hollowing process previously reported for Ag/Au nanowires and nanoparticles, with the difference that the involved length scales are 10–100 times larger. Specifically, we find that dry oxidation of Ag70Au30 bulk alloy samples by ozone exposure at 150 °C stimulates extremely rapid Ag outward diffusion toward the gas/alloy-surface interface, at rates at least 5 orders of magnitude faster than predicted on the basis of reported Ag bulk diffusion values. The micrometer-thick Ag depleted alloy region thus formed transforms into a 3D open nanoporous network morphology upon further exposure to methanol–O2 at 150 °C. These findings have important implications for practical applications of a...

To date, the primary focus of metal additive manufacturing (AM) research has been the development of strategies for fabricating complex architectures, reducing internal stress and optimizing microstructure. Traditional Al alloys have presented further challenges in this effort due to solidification cracking and complex laser coupling dynamics. To overcome these limitations, identification of novel alloys that exploit the rapid solidification conditions inherent in laser-based AM is required. In this work, laser-induced melting of an Al-8Ce-10Mg alloy is revealed to generate a nanoscale microstructure which results in improved hardness, tensile strength, and mitigated solidification cracking (e.g., hot tearing) in single laser tracks in as-cast material and laser powder bed fusion (LPBF)-fabricated components. In situ X-ray imaging shows the nanostructure arises from laser-induced melting of intermetallic particles embedded into the alloy during casting and then rapid resolidification of the molten material in ~ 400 µs. The formed Ce-rich nanostructures are highly resistant to thermal coarsening at 300 °C, as confirmed by microscopy and retention of tensile properties. These results pave the way for development of AM-specific Al alloys that possess the ability to form mechanically favorable nanostructures in fabricated components due to the rapid cooling inherent in LPBF.

Garnet-type solid electrolytes, such as Li6.4La3Zr1.4Ta0.6O12 (LLZTO), are promising materials for solid-state batteries, but processing remains a challenge, in part due to the high sintering temperature required for densification. This temperature can be lowered by decreasing the initial particle size via solvent-assisted ball milling, but the relationship between solvent choice, particle properties, sintering behavior, and ionic conductivity is not well understood. In this work, we systematically explore these parameters, showing that milling in commonly used protic solvents, such as alcohols, effectively decreases the particle size but results in lithium loss (through Li+/H+ exchange) that leads to poor sintering. By contrast, milling in aprotic solvents with surfactant reduces the particle size to ~220 nm without lithium loss, enabling the fabrication of dense samples (5.1 g/cm3) with good ionic conductivity (0.43 mS/cm at 25 °C) at a lower sintering temperature (1000 °C). We compare ionic conductivities and activation energies for samples prepared with different particle sizes and sintering temperatures and use multiphase-field simulations to identify the mass transport and microstructural mechanisms responsible for the observed sintering dependence on particle size. These results further clarify the relationship between processing parameters and performance and represent important progress toward overcoming fabrication challenges for these materials.

Graphene/metal oxide (GMO) nanocomposites promise a broad range of utilities for lithium ion batteries (LIBs), pseudocapacitors, catalysts, and sensors. When applied as anodes for LIBs, GMOs often exhibit high capacity, improved rate capability and cycling performance. Numerous studies have attributed these favorable properties to a passive role played by the exceptional electronic and mechanical properties of graphene in enabling metal oxides (MOs) to achieve near-theoretical capacities. In contrast, the effects of MOs on the active lithium storage mechanisms of graphene remain enigmatic. Via a unique two-step solvent-directed sol-gel process, we have synthesized and directly compared the electrochemical performance of several representative GMOs, namely Fe2O3/graphene, SnO2/graphene, and TiO2/graphene. We observe that MOs can play an equally important role in empowering graphene to achieve large reversible lithium storage capacity. The magnitude of capacity improvement is found to scale roughly with the surface coverage of MOs, and depend sensitively on the type of MOs. We define a synergistic factor based on the capacity contributions. Our quantitative assessments indicate that the synergistic effect is most achievable in conversion-reaction GMOs (Fe2O3/graphene and SnO2/graphene) but not in intercalation-based TiO2/graphene. However, a long cycle stability up to 2000 cycles was observed in TiO2/graphene nanocomposites. We propose a surface coverage model to qualitatively rationalize the beneficial roles of MOs to graphene. Our first-principles calculations further suggest that the extra lithium storage sites could result from the formation of Li2O at the interface with graphene during the conversion-reaction. These results suggest an effective pathway for reversible lithium storage in graphene and shift design paradigms for graphene-based electrodes.

Strengthening of metals through nanoscale grain boundaries and coherent twin boundaries is manifested by a maximum strength—a phenomenon known as Hall–Petch breakdown. Different softening mechanisms are considered to occur for nanocrystalline and nanotwinned materials. Here, we report nanocrystalline-nanotwinned Ag materials that exhibit two strength transitions dissimilar from the above mechanisms. Atomistic simulations show three distinct strength regions as twin spacing decreases, delineated by positive Hall–Petch strengthening to grain-boundary-dictated (near-zero Hall–Petch slope) mechanisms and to softening (negative Hall–Petch slope) induced by twin-boundary defects. An ideal maximum strength is reached for a range of twin spacings below 7 nm. We synthesized nanocrystalline-nanotwinned Ag with hardness 3.05 GPa—42% higher than the current record, by segregating trace concentrations of Cu impurity (

3D graphene foams exhibit immense degradation of mechanical properties. Micro-architecture can alleviate this problem, but no current technique meets the manufacturing requirements. Herein we developed a light-based 3D printing process to create hierarchical graphene structures with arbitrary complexity and order-of-magnitude finer features, showing enhanced mechanical properties at decreasing density.

Digitally controlled catalyst architectures via 3D printing potentially revolutionize the design of chemical plants., Monolithic nanoporous metals, derived from dealloying, have a unique bicontinuous solid/void structure that provides both large surface area and high electrical conductivity, making them ideal candidates for various energy applications. However, many of these applications would greatly benefit from the integration of an engineered hierarchical macroporous network structure that increases and directs mass transport. We report on 3D (three-dimensional)–printed hierarchical nanoporous gold (3DP-hnp-Au) with engineered nonrandom macroarchitectures by combining 3D printing and dealloying. The material exhibits three distinct structural length scales ranging from the digitally controlled macroporous network structure (10 to 1000 μm) to the nanoscale pore/ligament morphology (30 to 500 nm) controlled by dealloying. Supercapacitance, pressure drop, and catalysis measurements reveal that the 3D hierarchical nature of our printed nanoporous metals markedly improves mass transport and reaction rates for both liquids and gases. Our approach can be applied to a variety of alloy systems and has the potential to revolutionize the design of (electro-)chemical plants by changing the scaling relations between volume and catalyst surface area.

The effect of powder bed thickness and laser beam diameter on laser absorptivity is studied using micro-calorimetry. Dimensionless analysis is utilized to consolidate multiple influence factors into a single parameter for comparison between materials and laser parameters.

High energy light-ion (3.8 MeV He) bombardment is used to introduce lattice defects in a 3-dimensional (3D) interconnected network of graphene aerogels (GAs). When these materials are used as anodes for lithium ion batteries, we observe improved percentage reversible capacity and cycle stability compared to those without ion-beam treatment. Furthermore, all ion-beam treated 3D graphene samples exhibit substantially higher Coulombic efficiencies, suggesting at beneficial role of vacancy-type defects in stabilizing solid-electrolyte interphases. Although 3D graphene exhibits initial reversible capacities that are 2–3 times higher than that of graphite (∼372 mAh/g), fast capacity fading is observed but becomes more stable after ion-beam treatment. Our experimental results demonstrate that ion-beam treatment is an effective route to tune and produce good-performance graphene electrodes, and that vacancy-type defects help to promote reversible lithium storage capacity in graphene. We further observe that 3D GAs irradiated to the highest dose studied (10 16 cm −2 ) fail rapidly upon electrochemical cycling, likely caused by the excessive ion-beam damage and graphene restacking. Raman I (D)/ I (D′) signature is considered linked to defect type in graphene and thus is proposed, for the first time, as an indicator of the reversible capacity for GAs.

Although crystalline silicon (c-Si) anodes promise very high energy densities in Li-ion batteries, their practical use is complicated by amorphization, large volume expansion and severe plastic deformation upon lithium insertion. Recent experiments have revealed the existence of a sharp interface between crystalline Si (c-Si) and the amorphous Li[subscript x]Si alloy during lithiation, which propagates with a velocity that is orientation dependent; the resulting anisotropic swelling generates substantial strain concentrations that initiate cracks even in nanostructured Si. Here we describe a novel strategy to mitigate lithiation-induced fracture by using pristine c-Si structures with engineered anisometric morphologies that are deliberately designed to counteract the anisotropy in the crystalline/amorphous interface velocity. This produces a much more uniform volume expansion, significantly reducing strain concentration. Based on a new, validated methodology that improves previous models of aniso tropic swelling of c-Si, we propose optimal morphological designs for c-Si pillars and particles. The advantages of the new morphologies are clearly demonstrated by mesoscale simulations and verified by experiments on engineered c-Si micropillars. The results of this study illustrate that morphological design is effective in improving the fracture resistance of micron-sized Si electrodes, which will facilitate their practical application in next-generation Li-ion batteries. The model and design approach present in this paper also have general implications for the study and mitigation of mechanical failure of electrode materials that undergo large anisotropic volume change upon ion insertion and extraction., United States. Department of Energy (DE - SC0002626)

Much progress has recently been made in the development of active materials, electrode morphologies and electrolytes for lithium ion batteries. Well-defined studies on size effects of the three-dimensional (3D) electrode architecture, however, remain to be rare due to the lack of suitable material platforms where the critical length scales (such as pore size and thickness of the active material) can be freely and deterministically adjusted over a wide range without affecting the overall 3D morphology of the electrode. Here, we report on a systematic study on length scale effects on the electrochemical performance of model 3D np-Au/TiO2 core/shell electrodes. Bulk nanoporous gold provides deterministic control over the pore size and is used as a monolithic metallic scaffold and current collector. Extremely uniform and conformal TiO2 films of controlled thickness were deposited on the current collector by employing atomic layer deposition (ALD). Our experiments demonstrate profound performance improvements by matching the Li(+) diffusivity in the electrolyte and the solid state through adjusting pore size and thickness of the active coating which, for 200 μm thick porous electrodes, requires the presence of 100 nm pores. Decreasing the thickness of the TiO2 coating generally improves the power performance of the electrode by reducing the Li(+) diffusion pathway, enhancing the Li(+) solid solubility, and minimizing the voltage drop across the electrode/electrolyte interface. With the use of the optimized electrode morphology, supercapacitor-like power performance with lithium-ion-battery energy densities was realized. Our results provide the much-needed fundamental insight for the rational design of the 3D architecture of lithium ion battery electrodes with improved power performance.

Tuning the lattice degree of freedom in nanoscale functional crystals is critical to exploit the emerging functionalities such as piezoelectricity, shape-memory effect, or piezomagnetism, which are attributed to the intrinsic lattice-polar or lattice-spin coupling. Here it is reported that a mechanical probe can be a dynamic tool to switch the ferroic orders at the nanoscale multiferroic phase boundaries in BiFeO3 with a phase mixture, where the material can be reversibly transformed between the soft tetragonal-like and the hard rhombohedral-like structures. The microscopic origin of the nonvolatile mechanical switching of the multiferroic phase boundaries, coupled with a reversible 180 degrees rotation of the in-plane ferroelectric polarization, is the nanoscale pressure-induced elastic deformation and reconstruction of the spontaneous strain gradient across the multiferroic phase boundaries. The reversible control of the room-temperature multiple ferroic orders using a pure mechanical stimulus may bring us a new pathway to achieve the potential energy conversion and sensing applications.

The synthesis of ultralow-density (>5 mg/cm(3) ) bulk materials with interconnected nanotubular morphology and deterministic, fully tunable feature size, composition, and density is presented. A thin-walled nanotubular design realized by employing templating based on atomic layer deposition makes the material about 10 times stronger and stiffer than aerogels of the same density.

Porous titania/metal composite materials have many potential applications in the fields of green catalysis, energy harvesting, and storage in which both the overall morphology of the nanoporous host material and the crystallographic phase of the titania (TiO2) guest determine the material’s performance. New insights into the structure–function relationships of these materials were obtained by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy that, for example, provides quantitative crystallographic phase composition from ultrathin, nanostructured titania films, including sensitivity to amorphous components. Here, we demonstrate that crystallographic phase, morphology, and catalytic activity of TiO2-functionalized nanoporous gold (np-Au) can be controlled by a simple annealing procedure (T < 1300 K). The material was prepared by atomic layer deposition of ∼2 nm thick TiO2 on millimeter-sized samples of np-Au (40–50 nm mean ligament size) and catalytically investigated with respect to aerobic ...

Crystalline silicon nanostructures are commonly known to exhibit anisotropic expansion behavior during the lithiation that leads to grooving and fracture. Here we report surprisingly relatively uniform volume expansion behavior of large aspect-ratio (∼25), well-patterned, n-type (100) silicon micropillars (∼2 μm diameter) during the initial lithiation. The comparison results with and without atomic layer metal oxides (Al 2 O 3 and TiO 2 ) coatings reveal drastically enhanced solid electrolyte interphase (SEI) formation, higher volume expansion, and increased anisotropy. Square-pillars are found to exhibit nearly twice volume expansion without fracture compared to circular-pillars. Models are invoked to qualitatively address these beneficial or detrimental properties of silicon for lithium ion battery. Our experiments and computer simulations point at the critical relevance of SEI and pristine geometry in regulating volume expansion and failure. ALD-coated ultrathin metal oxides can act as an ion channel gate that helps promote fast Li + transport into the bulk by changing the surface kinetics, suggesting new ways of designing electrodes for high-performance lithium ion battery applications.

Solid-state batteries promise substantially higher energy densities and improved safety compared to traditional Li-ion batteries due to the replacement of flammable liquid electrolyte with solid-state materials. These advantages make them excellent candidates for next generation energy storage, but many processing and performance challenges must first be addressed. While several different types of solid-state electrolytes have been proposed, inorganic materials such as Li6.4La3Zr1.4Ta0.6O12 (LLZTO) have attracted much interest due to their high ionic conductivities and good mechanical and electrochemical properties. However, these materials are brittle and prone to large interfacial resistance, and many of the current fabrication techniques are difficult to scale up for manufacturing. 3D printing is an excellent tool to help solve some of these challenges, since it is scalable and capable of creating tailored architectures and compositions that can facilitate Li+ transport and reduce interfacial resistance. We report the development and optimization of ink formulations and processing conditions for 3D printed solid-state electrolytes. Since the electrolyte must be sintered after printing to densify the structure and achieve good ionic conductivity, initial particle size is an important consideration for both ink rheology and sintering success. We investigated the effect of milling solvent on particle size and lithium loss, both of which can affect the final ionic conductivity. In addition, while samples are traditionally mechanically pressed to aid densification during sintering, this technique cannot be used with printed architectures. Therefore, we explored other strategies to facilitate densification, including incorporating additional materials to act as sintering aids and optimizing ink composition and active material volume fraction. Samples were analyzed by SEM, XRD, and EIS to correlate processing and sintering conditions with electrochemical performance. Our results demonstrate significant progress toward 3D printing architected solid-state electrolytes with good ionic conductivity for high-energy-density solid-state batteries.

We report on the grain size dependent morphological, physical and chemical properties of thick microwave-plasma assisted chemical vapor deposited (MPCVD) diamond films that are used as target materials for high energy density physics experiments at the Lawrence Livermore National Laboratory. Control over the grain size, ranging from several μm to a few nm, was achieved by adjusting the CH4 content of the CH4/H2 feed gas. The effect of grain size on surface roughness, morphology, texture, density, hydrogen and graphitic carbon content was systematically studied by a variety of techniques. For depositions performed at 35 to 45 mbar and 3000 W microwave power (power density ~ 10 W cm− 3), an abrupt transition from micro-crystalline diamond to nanocrystalline diamond was observed at 3% CH4. This transition is accompanied by a dramatic decrease in surface roughness, a six percent drop in density and an increasing content in hydrogen and graphitic carbon impurities. Guided by these results, layered nano-microhybrid diamond samples were prepared by periodically changing the growth conditions from nano- to microcrystalline.

In this work, a systematical study of the stable shear banding behavior is performed across a wide range of alloy compositions of bulk metallic glasses (BMGs). Through microcompression, it can be demonstrated that the stable shear banding behavior could exhibit a dual character of stochastic and deterministic propagations. Different from the stochastic character, which is found insensitive to sample sizes, the deterministic character displays a clear trend of a sample size effect, which can be captured by the energy balance principle. Based on the theoretical framework laid out in this work, a correlation between the plastic energy dissipation and the sample size effect is established, which can be then utilized to explore the influence of the alloy’s chemical compositions on the behavior of shear-induced material softening. Finally, the energy-based formalisms aimed to quantify the shear banding size effect in MGs are discussed.

The microstructural features and micromechanical behavior of individual phases in a cast Al0.8CoCrCuFeNi high-entropy alloy (HEA) were characterized by high-resolution scanning electron microscopy and micro-compression tests. Use of neutron diffraction enabled the detection of a new phase which was otherwise unobservable by conventional X-ray diffraction. The identified phase constitution agreed well with the compositional analysis and the micro-compression results. The delicate microscale characterization of individual phase provides new insights for the design of novel HEAs with desirable mechanical properties. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.