Electrochemical catalyst design and optimization primarily relies on understanding and facilitating interfacial charge transfer. Recently, piezotronics have emerged as a promising method for tuning the interfacial energetics. The unique band-engineering capability using piezoelectric or ferroelectric polarization could lead to performance gains for electrochemical catalysis beyond what can be achieved by chemical or structural optimization. This article addresses the fundamentals of surface polarization and corresponding band modulation at solid–liquid interfaces. The most recent advances in piezotronic modulations are discussed from multiple perspectives of catalysis, including photocatalytic, photoelectrochemical, and electrochemical processes, particularly for energy-related applications. The concept of piezocatalysis, a direct conversion of mechanical energy to chemical energy, is introduced with an example of mechanically driven water splitting. While still in the early stages, piezotronics is envisioned to become a powerful tool for revolutionizing electrochemical catalysis.

We have investigated interfacial thermal resistance (ITR) between single-layer graphene and Cu substrate by using both experimental and numerical methods. For experiments, the micropipette sensing technique was utilized to measure the thermal conductivity of suspended graphene and temperature profile of supported graphene on Cu film subjected to heating with a point source continuous wave laser. The thermal conductivity of suspended single-layer graphene was measured to be 3492 ± 453 W/m°C from measurements of temperature profile on the suspended graphene. This intrinsic graphene thermal conductivity and the finite element method integrated with a multi-parameter fitting technique were used to estimate ITR between graphene and Cu film. In the multi-parameter fitting technique, the simulated temperature profile is compared with experimentally measured temperature profile on the supported graphene surface and the best-fitted parameters including thermal interface resistance was obtained. The estimated interface thermal resistance between single graphene and Cu substrate is 2.3 × 10−7 m2 K/W and the difference between experiment and simulation result during multi-parameter fitting is 6.9%.

Harnessing the nonvolatility of magnetism and the power of electric control, magnetoelectric devices that control magnetism electrically promise to deliver next-generation electronics systems that can store and compute large amounts of information with minimal power consumption and ultrafast processing speed. We highlight progress in magnetoelectric memory and logic prototypes using the voltage-controlled magnetic anisotropy (VCMA) effect. First, important performance metrics of VCMA-based magnetoelectric random access memory (MeRAM) are benchmarked against embedded complementary metal oxide semiconductor and other emerging embedded nonvolatile memories. We then discuss scaling of MeRAM from the physics and materials perspectives of the VCMA effect, as well as the use of magnetoelectric logic devices and circuits to realize new computing paradigms with VCMA. Finally, challenges to realize the full potential of VCMA-based memory and logic are presented: VCMA coefficient of 1000 fJ/V-m for energy-efficient write with low errors and tunneling magnetoresistance of 1000% for high density and low noise margin readout. New approaches for deterministic switching based on VCMA are needed. We share perspectives to address these challenges using new materials and device operation schemes.

A broadband magnetoelectric energy harvester, consisting of Fe1−xGax (Galfenol) as the magnetostrictor and a relaxor ferroelectric single crystal as the piezoelectric, has been designed and optimized. Finite element analysis (FEA) has been employed to show that either a linear displacement or a 180° rotation of a magnet is sufficient to achieve maximum stroke from the Galfenol rod, which induces a rhombohedral to orthorhombic phase transition in Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 that produces a large jump in voltage. A rotational design based on a pendulum with an unbalanced mass was fabricated and used to confirm the validity of our FEA model.

In fracture mechanics, established methods exist to model the stability of a crack tip or the kinetics of crack growth on both the atomic and the macroscopic scale. However, approaches to bridge the two scales still face the challenge in terms of directly converting the atomic forces at which bonds break into meaningful continuum mechanical failure stresses. Here we use two atomistic methods to investigate cleavage fracture of brittle materials: (i) we analyze the forces in front of a sharp crack and (ii) we study the bond breaking process during rigid body separation of half crystals without elastic relaxation. The comparison demonstrates the ability of the latter scheme, which is often used in ab initio density functional theory calculations, to model the bonding situation at a crack tip. Furthermore, we confirm the applicability of linear elastic fracture mechanics in the nanometer range close to crack tips in brittle materials. Based on these observations, a fracture mechanics model is developed to scale the critical atomic forces for bond breaking into relevant continuum mechanical quantities in the form of an atomistically informed scale-sensitive traction separation law. Such failure criteria can then be applied to describe fracture processes on larger length scales, e.g., in cohesive zone models or extended finite element models.

In this study, we have successfully grown hBN/graphene heterostructures on copper thin films using chemical vapor deposition in a single process. The first and most surprising result is that graphene grows underneath hBN and adjacent to the Cu film even though it is deposited second. This was determined from cross-sectional TEM analysis and XPS depth profiling, which chemically identified the relative positions of hBN and graphene. The effect of various growth conditions on graphene/hBN heterostructures was also studied. It was found that a pressure of 200 torr and a hydrogen flow rate of 200 sccm (∼1 H2/N2) yielded the highest quality of graphene, with full surface coverage occurring after a growth time of 120 min. The resulting graphene films were found to be approximately 6–8 layers thick. The grain size of the nanocrystalline graphene was found to be 15–50 nm varying based on growth conditions.

In this work, the guest Li+ conduction properties in NaBr–LiBH4 system were investigated. It was suggested that the guest Li+ ions occupy the Na+ sites and BH4− ions substitute the Br− ions in NaBr. The dominant Li+ conduction in NaBr–LiBH4 system was demonstrated by the combination of electrochemical measurements and time-of-flight secondary ion mass spectrometry. The guest Li+ ion conductivity of 15NaBr·LiBH4 was measured to be 1 × 10−7 S/cm at 313 K. The present results indicate that the guest Li+ conductors are not restricted to the previous reported iodides (NaI, KI), but other Li-free compounds have the possibility to become the candidates for the guest Li+ ion conductors.

Ti/Al/Mg/Al/Ti laminates were fabricated by hot rolling at 450 °C with various rolling reductions, and the relationship between the mechanical properties and microstructures was investigated in detail. Both Al–Mg and Ti–Al interfaces are well bonded without pore, crack, and intermetallics. Mg layer of 50% rolling reduction has the most dynamic recrystallized (DRXed) grains around the deformation bands, and tensile twins appear in Mg layer when the rolling reduction increases to 60%. Large numbers of twins are formed to absorb the further strain as reduction increases. Ti layer shows equiaxed grains, which are not sensitive to thickness strain. Mg layers of laminates with various rolling reductions all exhibit typical (0002) basal texture. Fifty-percent rolling reduction has the largest ultimate tensile strength of 337.8 MPa, which is mainly owing to grain refinement caused by the extensive DRX. The differences of elongation among the three samples with different rolling reductions are small.

In this study, the bioactivity and cytocompatibility of electrospun polyamide 6 (PA6)/hydroxyapatite (HA) coating on zirconia-toughened alumina (ZTA) were investigated. Adjusting the PA6/HA ratio to 1.15 (w/w) had a significant role in achieving an appropriate fibrous coating with an average diameter of 120 ± 10 nm and surface porosity of 64.3%. The surface of bare and coated samples was hydrophilic, which promoted bone regeneration. The adhesion test of the PA6/HA mat demonstrated that a cohesive coating was formed on the ZTA via electrospinning. The in vitro bioactivity test of the PA6/HA coating in simulated body fluid (SBF) corroborated the formation of a nanostructured bonelike apatite phase. Cytocompatibility of the samples was evaluated through in vitro osteosarcoma-like cell (MG63) culture assays. The cytotoxicity study showed that the electrospun PA6/HA coating significantly improved cell attachment and spreading. The development of such bioactive, biomedical coatings opens new avenues for bone tissue engineering applications.

Chitosan is an important cationic biopolymer widely used in various biomedical applications such as wound care, drug delivery, biomaterial scaffolds, and tissue engineering. In this work, hollow silica sphere (HSS) nanoparticles with an average size of 400–450 nm (via TEM) were synthesized by sol–gel process and were epoxidized using epichlorohydrin. Then, chitosan was chemically bound to the epoxidized HSS to form a bionanocomposite, HSS-epoxy-CHI-X where X represents the percentage of chitosan in the sample. BET analysis showed that pure HSS has a specific surface area (Ass) of around 4.8 m2/g and adsorption average pore diameter of 10.18 nm. Bionanocomposites were characterized by FT-IR spectroscopy to confirm the bonding of chitosan on HSS nanoparticles. X-ray diffraction studies demonstrated that the amorphous character of the materials improved with the HSS content. Thermogravimetric analysis illustrated that at low temperatures, the thermal stability of bionanocomposites was higher than that of the sample with no chitosan in it. Scanning electron microscopic analysis results confirmed the homogenous distribution of HSS in the bionanocomposites. Considering the biological activity of chitosan and absorption characteristics of HSS, newly developed HSS-epoxy-CHI-X bionanocomposites were tested for wound healing by in vitro scratch assay using NIH 3T3 fibroblast cells. Among the bionanocomposites analyzed, HSS-epoxy-CHI-60 exhibited better performance where about 90% wound closure was observed for this sample after 21 h of exposure.

Bimodal nanoporous platinum (BNP-Pt) is synthesized by using a sacrificial nanoporous copper (NP-Cu) support for oxygen-reduction-reaction (ORR) catalysts in fuel cells. The specific ORR catalytic activity of BNP-Pt increases by the dissolution and removal of supporting NP-Cu, suggesting that the BNP structure improves the intrinsic catalytic properties of platinum. The lattice contraction of BNP-Pt containing residual copper even after NP-Cu removal is milder than predicted by Vegard's law. The BNP structure governs the intrinsic catalytic activity of the platinum by relaxing the lattice contraction and by alloying with copper and/or misfit strain at the Pt/Cu interface.

The effect of SiCp on the aging behavior of the extruded SiCp/AZ91 composite fabricated by stir casting was investigated in detail. The necklace-type distribution of the particles in the cast SiCp/AZ91 composite was destroyed, and the extrusion bands consisting of SiCp and small dynamic recrystallized grains formed aligning along the extrusion direction. Addition of SiCp could accelerate the aging kinetics of the AZ91 matrix because of the overlapped particle plastic zone. The improved particle distribution and refined grains caused by the recrystallization could affect the aging behavior of the SiCp/AZ91 composite. The Mg17A112 discontinuous precipitates preferred to nucleate at the SiC/Mg interfaces and the grain boundaries within the extrusion bands and then expanded into the particle-free region. Moreover, the promoted discontinuous precipitates would suppress the continuous intragranular precipitates with respect to the unreinforced AZ91 alloy.