Strain-Induced Large Exciton Energy Shifts in Buckled CdS Nanowires

Strain engineering can be utilized to tune the fundamental properties of semiconductor materials for applications in advanced electronic and photonic devices. Recently, the effects of large strain on the properties of nanostructures are being intensely investigated to further expand our insights into the physics and applications of such materials. In this Letter, we present results on controllable buckled cadmium-sulfide (CdS) optical nanowires (NWs), which show extremely large energy bandgap tuning by >250 meV with applied strains within the elastic deformation limit. Polarization and spatially resolved optical measurements reveal characteristics related to both compressive and tensile regimes, while microreflectance spectroscopy clearly demonstrates the effect of strain on the different types of excitons in CdS. Our results may enable strained NWs-based optoelectronic devices with tunable optical responses

Highly Stretchable and Notch-Insensitive Hydrogel Based on Polyacrylamide and Milk Protein

Protein-based hydrogels have received attention for biomedical applications and tissue engineering because they are biocompatible and abundant. However, the poor mechanical properties of these hydrogels remain a hurdle for practical use. We have developed a highly stretchable and notch-insensitive hydrogel by integrating casein micelles into polyacrylamide (PAAm) networks. In the casein-PAAm hybrid gels, casein micelles and polyacrylamide chains synergistically enhance the mechanical properties. Casein-PAAm hybrid gels are highly stretchable, stretching to more than 35 times their initial length under uniaxial tension. The hybrid gels are notch-insensitive and tough with a fracture energy of approximately 3000 J/m². A new mechanism of energy dissipation that includes friction between casein micelles and plastic deformation of casein micelles was suggested

Dehydrogenation Reaction Pathway of the LiBH₄–MgH₂ Composite under Various Pressure Conditions

This paper investigates dehydrogenation reaction behavior of the LiBH₄–MgH₂ composite at 450 °C under various hydrogen and argon back-pressure conditions. While the individual decompositions of LiBH₄ and MgH₂ simultaneously occur under 0.1 MPa H₂, the dehydrogenation of MgH₂ into Mg first takes place and subsequent reaction between LiBH₄ and Mg into LiH and MgB₂ after an incubation period under 0.5 MPa H₂. Under 1 MPa H₂, enhanced dehydrogenation kinetics for the same reaction pathway as that under 0.5 MPa H₂ is obtained without the incubation period. However, the dehydrogenation reaction is significantly suppressed under 2 MPa H₂. The formation of Li₂B₁₂H₁₂ as an intermediate product during dehydrogenation seems to be responsible for the incubation period. The degradation in hydrogen capacity during hydrogen sorption cycles is not prevented with the dehydrogenation under 1 MPa H₂, which effectively suppresses the formation of Li₂B₁₂H₁₂. The overall dehydrogenation behavior under argon pressure conditions is similar to that at hydrogen pressure conditions, except that under 2 MPa Ar

Enhanced Li Ion Conductivity in LiBH₄–Al₂O₃ Mixture via Interface Engineering

A new solid-state Li ion conductor composed of LiBH₄ and Al₂O₃ was synthesized by a simple ball-milling process. The element distribution map obtained by transmission electron microscopy demonstrates that the LiBH₄ and Al₂O₃ are well mixed and form a large interface after ball-milling. The ionic conductivity of the mixture reaches as high as 2 × 10^–4 S cm^–1 at room temperature when the volume fraction of Al₂O₃ is approximately 44%. The ionic conductivity of the interface between LiBH₄ and Al₂O₃ was extracted by using a continuum percolation model, which turns out to be about 10^–3 S cm^–1 at room temperature, being 10⁵ times higher than that of pure LiBH₄. This remarkable rise in conductivity is accompanied by the lowered activation energy for the Li ion conduction in the mixture, indicating that the interface layer facilitates Li ion conduction. Near-edge X-ray absorption fine structure analysis reveals the presence of B–O bondings in the mixture, which was not detected by X-ray diffraction. This disruption of the chemical bondings at the interface may allow an increase in carrier concentration and/or mobility thereby resulting in the pronounced enhancement in conductivity. This result provides a guideline for designing fast Li ion conductor through interface engineering

Face-Centered-Cubic Lithium Crystals Formed in Mesopores of Carbon Nanofiber Electrodes

In the foreseeable future, there will be a sharp increase in the demand for flexible Li-ion batteries. One of the most important components of such batteries will be a freestanding electrode, because the traditional electrodes are easily damaged by repeated deformations. The mechanical sustainability of carbon-based freestanding electrodes subjected to repeated electrochemical reactions with Li ions is investigated <i>via</i> nanotensile tests of individual hollow carbon nanofibers (HCNFs). Surprisingly, the mechanical properties of such electrodes are improved by repeated electrochemical reactions with Li ions, which is contrary to the conventional wisdom that the mechanical sustainability of carbon-based electrodes should be degraded by repeated electrochemical reactions. Microscopic studies reveal a reinforcing mechanism behind this improvement, namely, that inserted Li ions form irreversible face-centered-cubic (FCC) crystals within HCNF cavities, which can reinforce the carbonaceous matrix as strong second-phase particles. These FCC Li crystals formed within the carbon matrix create tremendous potential for HCNFs as freestanding electrodes for flexible batteries, but they also contribute to the irreversible (and thus low) capacity of HCNFs

Centimeter-Scale 2D van der Waals Vertical Heterostructures Integrated on Deformable Substrates Enabled by Gold Sacrificial Layer-Assisted Growth

Two-dimensional (2D) transition metal dichalcogenides (TMDs) such as molybdenum or tungsten disulfides (MoS₂ or WS₂) exhibit extremely large in-plane strain limits and unusual optical/electrical properties, offering unprecedented opportunities for flexible electronics/optoelectronics in new form factors. In order for them to be technologically viable building-blocks for such emerging technologies, it is critically demanded to grow/integrate them onto flexible or arbitrary-shaped substrates on a large wafer-scale compatible with the prevailing microelectronics processes. However, conventional approaches to assemble them on such unconventional substrates via mechanical exfoliations or coevaporation chemical growths have been limited to small-area transfers of 2D TMD layers with uncontrolled spatial homogeneity. Moreover, additional processes involving a prolonged exposure to strong chemical etchants have been required for the separation of as-grown 2D layers, which is detrimental to their material properties. Herein, we report a viable strategy to universally combine the centimeter-scale growth of various 2D TMD layers and their direct assemblies on mechanically deformable substrates. By exploring the water-assisted debonding of gold (Au) interfaced with silicon dioxide (SiO₂), we demonstrate the direct growth, transfer, and integration of 2D TMD layers and heterostructures such as 2D MoS₂ and 2D MoS₂/WS₂ vertical stacks on centimeter-scale plastic and metal foil substrates. We identify the dual function of the Au layer as a growth substrate as well as a sacrificial layer which facilitates 2D layer transfer. Furthermore, we demonstrate the versatility of this integration approach by fabricating centimeter-scale 2D MoS₂/single walled carbon nanotube (SWNT) vertical heterojunctions which exhibit current rectification and photoresponse. This study opens a pathway to explore large-scale 2D TMD van der Waals layers as device building blocks for emerging mechanically deformable electronics/optoelectronics

Biofunctionalized Ceramic with Self-Assembled Networks of Nanochannels

Nature designs circulatory systems with hierarchically organized networks of gradually tapered channels ranging from micrometer to nanometer in diameter. In most hard tissues in biological systems, fluid, gases, nutrients and wastes are constantly exchanged through such networks. Here, we developed a biologically inspired, hierarchically organized structure in ceramic to achieve effective permeation with minimum void region, using fabrication methods that create a long-range, highly interconnected nanochannel system in a ceramic biomaterial. This design of a synthetic model-material was implemented through a novel pressurized sintering process formulated to induce a gradual tapering in channel diameter based on pressure-dependent polymer agglomeration. The resulting system allows long-range, efficient transport of fluid and nutrients into sites and interfaces that conventional fluid conduction cannot reach without external force. We demonstrate the ability of mammalian bone-forming cells placed at the distal transport termination of the nanochannel system to proliferate in a manner dependent solely upon the supply of media by the self-powering nanochannels. This approach mimics the significant contribution that nanochannel transport plays in maintaining living hard tissues by providing nutrient supply that facilitates cell growth and differentiation, and thereby makes the ceramic composite “alive”