Driving the field of micro computed tomography toward more quantitative, rather than qualitative, approaches, we here present a new evaluation method, which uses the unique linear relationship between gray values and x-ray attenuation coefficients, together with the energy-dependence of the latter, to identify (i) the average x-ray energy used in the CT device, (ii) the x-ray attenuation coefficients, and (iii), via the x-ray attenuation average rule, the intravoxel composition, i.e., the microporosity, which, amongst others, governs the voxel-specific mechanical properties, such as stiffness and strength. The method is realized for six 3D tricalcium phosphate scaffolds, seeded with pre-osteoblastic cells and differentiated for 3, 6, and 8 weeks, respectively. The corresponding voxel-specific microporosities turn out to increase during the culturing period (resulting in reduced elastic properties, as determined from micromechanical considerations), while the overall macroporosity remains constant. The new methods are expected to further foster the development of a rationally based and computer-aided design of biomaterials and tissue engineering scaffolds.

Porous, strong, and stiff ceramic materials are required for a range of technical applications, involving for instance, liquid or gas flow. Natural materials such as wood can provide useful structural guidelines for the optimal microstructural design, although only few processing routes are able to turn these guidelines into actual materials. We illustrate here, how ice templating of anisotropic particle suspensions can be modified to obtain a honeycomb structure with pores of 30 µm diameter. The growth of ice crystals in the slurry induces self-assembly of the anisotropic particles, leading to relatively thin walls (10 µm). Because large anisotropic particles are difficult to sinter, a glassy phase was introduced to facilitate this densification step and then to further reduce the walls' porosity. Young's modulus and compressive strength were both improved by the addition of a glassy phase by an order of magnitude due to the denser walls. These macroporous materials are more robust and stiff than materials with an equivalent morphology, while offering a simple alternative to the current wood replica processing routes.

Proximity effects and exchange coupling across interfaces of hybrid magnetic heterostructures present unique opportunities for functional material design. In this review, we present an overview of recent experiments on magnetic hybrid materials in which magnetism was controlled by proximity to an active material. In particular, we discuss interfacial strain coupling of ferromagnetic materials in contact with a material undergoing a structural deformation. Bilayers containing VO2 and V2O3 as active materials are shown to strongly affect the magnetization and coercivity of ferromagnetic materials due to stress anisotropy caused by a temperature-dependent structural displacement in the oxide. The possibilities of tuning the system by sample morphology and materials choice are discussed in detail. In addition, we highlight a length-scale competition between magnetic and structural domains which leads to a maximum change in the coercivity in a narrow temperature window of the vanadium oxide phase transition.

NiO nanoplatelet-based materials with different dimensionality are synthesized by a one-step hydrothermal route at 120 °C for 4 h. The morphologies and structure of the obtained NiO nanoplatelets grown on Ni foam and NiO microspheres composed of nanoplatelets are characterized. The results show that the former has a length of 5–10 μm and a uniform thickness of ∼100 nm, while the latter has a diameter of 5–10 μm. Their electrochemical properties as anode materials for lithium-ion batteries are evaluated and compared. The discharge capacities of NiO nanoplatelet electrode are 663, 516, 370, 258, and 169 mAh g−1 at current densities of 250, 500, 1000, 2500, and 5000 mA g−1, respectively. Such a lithium storage capability is much higher than that of the NiO microsphere electrode. The reasons for the enhanced electrochemical performance of the nanoplatelet electrode were investigated, which suggested that more active sites for electrochemical reactions and faster ion/electron transfer realized on nanoplatelets are facilitating lithium storage.

In this study, a conductive polymer, poly(3,4-ethylenedioxythiophene) or PEDOT, was used as binder in the sulfur electrode to study electrochemical performance of lithium–sulfur (Li–S) batteries. PEDOT-based sulfur electrode was compared with that of polyvinylidene difluoride binder based sulfur electrode. Different particle size sulfur materials including commercial micrometric sulfur particles and synthesized colloidal nanometric sulfur powders were chosen as active materials to study the impact of particle size on the cell performance. Different electrolytes including lithium bis(trifluoromethanesulfonyl)imide in polyethylene glycol dimethyl ether (PEGDME) or 1,3-dioxolane-dimethoxy ethane were used in the Li–S batteries to investigate the impact of electrolyte on cell performance. The PEDOT and micrometric sulfur based electrode with PEGDME electrolyte had the best cycle performance, which showed a capacity retention of 68% and specific capacity of 578 mAh/g after 100 cycles. The increased conductivity by conductive polymer and the high viscosity of PEGDME play important roles in the improvement of cycle performance.

We investigate the effect of dopant species and structure on the thermal conductivity of Sb-doped SnO2 (ATO) and Ta-doped SnO2 (TTO) films and compare the results with those of In2O3-, ZnO-, and TiO2-based transparent conductive films. The thermal conductivities (λ) of polycrystalline ATO and TTO films are 4.4–4.9 and 4.7 W m−1 K−1, respectively. The thermal conductivities via phonons (λph) are almost identical for both dopant species (Sb and Ta): 4.3 and 4.5 W m−1 K−1 for Sb and Ta, respectively, on average. These results for λph are larger than that for Sn-doped In2O3 films (3.8 W m−1 K−1) and considerably larger than that for amorphous ATO films (1.0 W m−1 K−1). These facts lead us to conclude that the base-material species (SnO2 or In2O3) and structure (polycrystalline or amorphous) affect the thermophysical properties of ATO and TTO much more than the dopant species.

Groups of chloromethyl were randomly grafted to Janus composite particles and quaternization was carried out on the particles. The Janus material of titania–quaternary ammoniated poly(vinylbenzyl chloride–divinylbenzene) (TiO2–QApoly(VBC–DVB)) was investigated in detail. Results revealed that the anisotropic Janus material containing quaternary ammonium groups was synthesized successfully. The Janus material could be used as the phase transfer catalyst. The catalytic activity of the Janus material was confirmed by the esterification reaction of benzyl chloride and sodium acetate. In the presence of 0.5 wt.% (relative to benzyl chloride) of TiO2–QApoly(VBC–DVB), the esterification yield of benzyl acetate reached 87.6% when the molar ratio of sodium acetate anhydrous to benzyl chloride was 1.2. The catalyst exhibited a high activity and had no obvious loss of activity when recycled three times. Moreover, the Janus material was easily recovered by centrifugation and washed with ethanol and water.

Bulk metallic glasses (BMGs) exhibit high yield strength but little tensile ductility. For this class of materials, damage tolerance is a key mechanical design parameter needed for their engineering use. Recently we have discovered a correlation between the local structural characteristics in the glass and the propensity for shear transformations. Based on the dependence of glass structure on alloy composition, zirconium (Zr)-rich Zr–titanium (Ti)–copper (Cu)–aluminum (Al) compositions are predicted to be more prone to spread-out plastic deformation and hence profuse shear banding. This structural perspective has guided us to locate a Zr61Ti2Cu25Al12 (ZT1) BMG that exhibits a record-breaking fracture toughness, on par with the palladium (Pd)-based BMG recently developed at Caltech. At the same time, the new BMG consists of common metals and has robust glass-forming ability. Interestingly, the ZT1 BMG derives its high toughness from its high propensity for crack deflection and local loading-mode change (from mode I to substantially mode II) at the crack tip due to extensive shear band interactions. A crack-resistance curve (R-curve) has been obtained following American Society for Testing and Materials (ASTM) standards, employing both “single-specimen” and “multiple-specimen” techniques as well as fatigue precracked specimens. The combination of high strength and fracture toughness places ZT1 atop all engineering metallic alloys in the strength–toughness Ashby diagram, pushing the envelop accessible to a structural material in terms of its damage tolerance.

Scanning electron microscopic (SEM) observations revealed that individual and independent microcones of sp3-bonded boron nitride grown by laser-activated plasma chemical vapor deposition were accompanied by ripple patterns spreading around them in the dimension of micrometers or sub-micrometers. The ripples were expanding equidistantly from each other and diminishing as they depart from a cone. The origin of the ripples was attributed to the interference of a direct laser cast on the plane surface and that reflected from the side of a cone; this model was satisfactorily in agreement with the SEM measurement, in which the side surface of a cone was mapped onto the plane surface surrounding the cone in the mathematical meaning of “bijection.” This micro-optical effect due to the wave nature of laser was considered to indicate and support the photochemically activated growth reactions in this process.

We derive the dispersion relation of SiC substrate phonon-induced surface plasmon polariton (SPP) in epitaxial graphene (EG) grown on 4H–SiC, in SiC's restrahlen band (8–10 μm) by solving Maxwell equation in transverse magnetic mode. We also fabricated EG waveguide using photolithography and RIE etching for experimental study. Both theory and experimental data correlate in good agreement. Finally, we explain the viability of plasmonic device in EG both in theoretical and experimental point of view to explain electron–hole pair recombination. SPP formation finds application in nanophotonic devices for optical computing because of graphene's unique plasmonic properties. This can be applicable for high speed data switching in microprocessor and random access memory as well as optical interconnect in modern VLSI technology.

Active research is ongoing in logic devices beyond complementary metal–oxide–semiconductor electronics. One of the most promising classes of such devices is spintronic/nanomagnetic devices. Switching of magnetization by spin torque (ST) demonstrated in spintronic devices results in relatively high switching energy. An attractive option for lowering switching energy is magnetoelectric (ME) switching achieved by placing other materials (mostly oxides) adjacent to ferromagnets. We review recent experiments on ME switching, classify them according to the ME phenomena into surface anisotropy, exchange bias, and magnetostrictive, and compare switching parameters for these classes. Then, we perform micromagnetic simulations of switching by the effective ME field of both stand-alone nanomagnets and spintronic interconnects. We determine the threshold values of ME field for switching and the resulting switching time. These switching requirements are incorporated into the previously developed benchmarking framework for spintronic logic devices and circuits. We conclude that ME switching results in 1 to 2 orders of magnitude improvement of switching energy and several time improvement of switching delay compared with ST switching across various schemes of spin logic devices.

The rapid sol–gel synthesis of macroscopic quantities of nanodiamond aerogel (NDAG) is reported at standard temperature and pressure using acid-catalyzed covalent crosslinking of air-oxidized detonation nanodiamond (DND) nanocrystals. Acetonitrile acts as a polar, aprotic solvent both to form a colloidal dispersion of DND particles and to conduct acid-catalyzed polycondensation reactions between resorcinol and formaldehyde (RF) small molecule precursors. Several characterization techniques show that nanodiamond grains are connected via covalent bonding with RF molecules to form a porous, three-dimensional network. Solvent exchange into liquid carbon dioxide and subsequent supercritical drying of NDAGs are used to recover low-density (151 mg/cm3), three-dimensional monolithic aerogels that exhibit surface areas in excess of 589 m2/g. The large accessible pore volume from the rapidly synthesized, macroscopic NDAG materials suggests a range of potential applications in catalysis, sensing, energy storage, as well as inert excipients for small-molecule pharmaceuticals.

Piezoresistance (PZR) is the change in the electrical resistivity of a solid induced by an applied mechanical stress. Its origin in bulk crystalline materials like silicon is principally a change in the electronic structure which leads to a modification of the effective mass of charge carriers. The past few years have seen a rising interest in the PZR properties of semiconductor nanostructures, motivated in part by claims of a giant PZR (GPZR) in silicon nanowires more than two orders of magnitude bigger than the known bulk effect. This review aims to present the controversy surrounding claims and counterclaims of GPZR in silicon nanostructures by summarizing the major works carried out over the past 10 years. The main conclusions to be drawn from the literature are that (i) reproducible evidence for a GPZR in ungated nanowires is limited; (ii) in gated nanowires, GPZR has been reproduced by several authors; (iii) the giant effect is fundamentally different from either the bulk silicon PZR or that resulting from quantum confinement, the evidence pointing to an electrostatic origin; (iv) released nanowires tend to have slightly larger PZR than unreleased nanowires; and (v) insufficient work has been performed on bottom-up grown nanowires to be able to rule out a fundamental difference in their properties when compared with top-down nanowires. On the basis of this, future possible research directions are suggested.

The mesoporous and nanorods SnO2 are synthesized by controlling the state of SnCl2·2H2O precursor with SBA-15 as hard template, and the possible formation mechanisms at different assembling modes inside the ordered mesoporous silica templates are proposed. In addition, SnO2 nanoparticles are synthesized by hydrolysis depositing method. The electrochemical tests of as-prepared samples indicate that the reticular stacking structure of the nanorods would limit the Li+ ions to intercalate, but the effect of volume expansion in this case upon cycling is insignificant. The mesostructure SnO2 tends to be stable after partial structural collapse at first few cycles. And the Li+ ions can readily intercalate and de-intercalate into/from its ordered channels structure, which provides a high capacity and an improved cycle property. Although SnO2 nanoparticles deliver high capacity at an early stage, the agglomeration may induce the capacity to drop rapidly after a certain number of cycles.

Solid oxide fuel cells (SOFCs) offer an efficient energy conversion technology for alleviating current energy problems. High temperature proton-conducting (HTPC) oxides are promising electrolytes for this technology, since their activation energy is lower than that of conventional oxygen-ion conductors, enabling the operating temperature reduction at 600 °C. Among HTPC oxides, doped BaZrO3 materials possess high chemical stability, needed for practical applications. Though, poor sinterability and the resulting large volume of highly resistive grain boundaries hindered their deployment for many years. Nonetheless, the recently demonstrated high proton conductivity of the bulk revived the attention on doped BaZrO3, stimulating research on solving the sintering issues. The proper selection of dopants and sintering aids was demonstrated to be successful for improving the BaZrO3 electrolyte sinterability. We here briefly review the synthesis strategies proposed for preparing BaZrO3-based nanostructured powders for electrolyte and electrodes, with the aim to improve the SOFC performance.

Thin film silicon tandem junction solar cells based on amorphous silicon (a-Si:H) and microcrystalline silicon (µc-Si:H) were developed with focus on high open-circuit voltages for the application as photocathodes in integrated photoelectrochemical cells for water electrolysis. By adjusting various parameters in the plasma enhanced chemical vapor deposition process of the individual µc-Si:H single junction solar cells, we showed that a-Si:H/µc-Si:H tandem junction solar cells exhibit open-circuit voltage over 1.5 V with solar energy conversion efficiency of 11% at a total silicon layer thickness below 1 µm. Our approach included thickness reduction, controlled SiH4 profiling, and incorporation of intrinsic interface buffer layers. The applicability of the tandem devices as photocathodes was evaluated in a photoelectrochemical cell. The a-Si:H/µc-Si:H based photocathodes exhibit a photocurrent onset potential of 1.3 V versus RHE and a short-circuit photocurrent of 10.0 mA/cm2. The presented approach may provide an efficient and low-cost pathway to solar hydrogen production.

This article presents a new multiscale modeling approach proposed to predict the impact response of a biomedical niobium–zirconium alloy by incorporating both geometric and microstructural aspects. Specifically, the roles of both anisotropy and geometry-based distribution of stresses and strains upon loading were successfully taken into account by incorporating a proper multiaxial material flow rule obtained from crystal plasticity simulations into the finite element (FE) analysis. The simulation results demonstrate that the current approach, which defines a hardening rule based on the location-dependent equivalent stresses and strains, yields more reliable results as compared with the classical FE approach, where the hardening rule is based on the experimental uniaxial deformation response of the material. This emphasizes the need for proper coupling of crystal plasticity and FE analysis for the sake of reliable predictions, and the approach presented herein constitutes an efficient guideline for the design process of dental and orthopedic implants that are subject to impact loading in service.

Microwave irradiation has the potential to affect the mechanical properties of natural silks. We explored several tensile properties of Bombyx mori silkworm cocoon fibers (yield stress and strain, breaking stress and strain, Young's modulus, toughness) as a function of microwave exposure time; samples were stored in a desiccating environment prior to tensile testing. Microwave radiation did not significantly affect any of these properties. We conclude that silk can be incorporated as a reinforcing fiber—without significant deterioration in properties—into materials that are subjected to microwave processing and/or in-service microwave radiation. Microwave exposure decreased the Weibull modulus of fibers, indicating that fracture becomes less predictable as a result of the exposure. Since microwave exposure affects failure predictability but not the average breaking strength of fibers, silk is best suited for use in composite materials if microwave exposure is likely, so that load can be transferred from weaker to stronger fibers.