Diffusion and Surface Effects on Sodium-Promoted MoS Growth Observed in Operando.

Understanding precursor diffusion and substrate interaction is key to advancing chemical vapor deposition (CVD) of transition metal dichalcogenides (TMCs), yet direct observation has remained a challenge due to limited real-time observation. Here, MoS growth is directly monitored to investigate the kinetics and influence of the precursor/sodium droplet eutectic (SODE). Serving as a catalyst, SODE migrates from the basal plane to the edges and substrate interface, promoting growth and enabling grain translation and rotation.

Residue-Free Fabrication of van der Waals Heterostructures of Two-Dimensional Materials.

In this work, a unique methodology is presented that utilizes van der Waals (vdW) interactions to fabricate residue-free single flakes of two-dimensional (2D) materials, which are subsequently assembled into intricate heterostructures. The approach focuses on ensuring that the flakes are free from any residue that could affect their properties and performance. Evidence from atomic force microscopy and Raman spectroscopy confirms that the transferred hexagonal boron nitride (h-BN) and molybdenum disulfide (MoS2) flakes exhibit excellent flatness and strain-free characteristics, which are crucial for various applications in electronics and optoelectronics.

Improved Polydimethylsiloxane (PDMS) Double Casting via Silicone Oil Treatment for Densely Packed Microstructure Replication.

Polydimethylsiloxane (PDMS) double casting is widely used for replicating microscale structures, including microfluidic channels and biomedical microdevices such as Bio-MEMS. Despite its versatility, strong interfacial adhesion between PDMS layers often results in incomplete replication or structural damage, particularly in densely packed microfeatures. Conventional approaches to reduce adhesion, such as plasma or chemical surface modification, require specialized equipment and can be time-consuming and costly.

Se-Assisted Modulation of Electronic Structure of Ruthenium Phosphide Nanotubes for Efficient Alkaline Hydrogen Evolution Reaction.

Anion-exchange membrane water electrolysis (AEMWE) holds immense promise for hydrogen (H) production yet faces challenges due to the sluggish kinetics of the hydrogen evolution reaction (HER). Highly efficient and durable catalysts for HER are crucial for the successful implementation of AEMWE to produce hydrogen gas reliably. Ruthenium phosphides (Ru P) have emerged as promising non-Pt catalysts for alkaline HER; however, they suffer from rapid degradation due to weak Ru-P bonding, which cannot protect the Ru center from further oxidation and subsequent dissolution.

Residue-Free Fabrication of 2D Materials Using van der Waals Interactions.

2D materials have garnered considerable attention due to their distinctive properties, prompting diverse applications across various domains. Beyond their inherent qualities, the significance of 2D materials extends into the fabrication processes that can lead to the degradation of intrinsic performance through undesirable mechanical defects and surface contaminations. Herein, a novel fabrication technique to achieve residue-free 2D materials using van der Waals (vdW) interactions, primarily employing molybdenum disulfide (MoS) is proposed.

Expanding the frontiers of electrocatalysis: advanced theoretical methods for water splitting.

Electrochemical water splitting, which encompasses the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), offers a promising route for sustainable hydrogen production. The development of efficient and cost-effective electrocatalysts is crucial for advancing this technology, especially given the reliance on expensive transition metals, such as Pt and Ir, in traditional catalysts. This review highlights recent advances in the design and optimization of electrocatalysts, focusing on density functional theory (DFT) as a key tool for understanding and improving catalytic performance in the HER and OER.

Quasiballistic thermal transport in submicron-scale graphene nanoribbons at room-temperature.

Phonon transport in two-dimensional materials has been the subject of intensive studies both theoretically and experimentally. Recently observed unique phenomena such as Poiseuille flow at low temperature in graphene nanoribbons (GNRs) initiated strong interest in similar effects at higher temperatures. Here, we carry out massive molecular dynamics simulations to examine thermal transport in GNRs at room temperature (RT) and demonstrate that non-diffusive behaviors including Poiseuille-like local thermal conductivity and second sound are obtained, indicating quasiballistic thermal transport.

All-dielectric polarization-sensitive metasurface for terahertz polarimetric imaging.

Terahertz polarimetric imaging, capable of capturing not only intensity profiles but also the polarization states of the incident pattern, is an essential technique with promising applications such as security scans and medical diagnoses. Recently, a novel approach for terahertz imaging has been proposed using a metasurface absorber that converts terahertz light into a temperature profile. However, polarization remains indistinguishable in the imaging process due to the isotropic geometry of the metasurface.

High-Field Electron Transport and High Saturation Velocity in Multilayer Indium Selenide Transistors.

Creating a high-frequency electron system demands a high saturation velocity (υ). Herein, we report the high-field transport properties of multilayer van der Waals (vdW) indium selenide (InSe). The InSe is on a hexagonal boron nitride substrate and encapsulated by a thin, noncontinuous In layer, resulting in an impressive electron mobility reaching 2600 cm/(V s) at room temperature.

Electromagnetic Interference Shield of Highly Thermal-Conducting, Light-Weight, and Flexible Electrospun Nylon 66 Nanofiber-Silver Multi-Layer Film.

A light-weight, flexible electromagnetic interference (EMI) shield was prepared by creating a layer-structured metal-polymer composite film consisting of electrospun nylon 66 nanofibers with silver films. The EMI shielding effectiveness (SE), specific SE, and absolute SE of the composite were as high as 60.6 dB, 67.

Active photonic wireless power transfer into live tissues.

Recent advances in soft materials and mechanics activate development of many new types of electrical medical implants. Electronic implants that provide exceptional functions, however, usually require more electrical power, resulting in shorter period of usages although many approaches have been suggested to harvest electrical power in human bodies by resolving the issues related to power density, biocompatibility, tissue damage, and others. Here, we report an active photonic power transfer approach at the level of a full system to secure sustainable electrical power in human bodies.

Crosslinking Effect on Thermal Conductivity of Electrospun Poly(acrylic acid) Nanofibers.

The thermal conductivity () of poly(acrylic acid) (PAA) nanofibers, which were electrospun at various electrospinning voltages, was measured using suspended microdevices. While the thermal conductivities of the as-spun PAA nanofibers varied depending on the electrospinning voltages, the most pronounced 3.1-fold increase in thermal conductivity in comparison to that of bulk PAA was observed at the electrospinning voltage of 14 kV.

Thermal conductivity enhancement in electrospun poly(vinyl alcohol) and poly(vinyl alcohol)/cellulose nanocrystal composite nanofibers.

The thermal conductivity enhancement of neat poly(vinyl alcohol) and poly(vinyl alcohol) (PVA)/cellulose nanocrystal (CNC) composite was attempted via electrospinning. The suspended microdevice technique was applied to measure the thermal conductivity of electrospun nanofibers (NFs). Neat PVA NFs and PVA/CNC NFs with a diameter of approximately 200 nm showed thermal conductivities of 1.

Effects of β-sheet crystals and a glycine-rich matrix on the thermal conductivity of spider dragline silk.

We measured the thermal conductivity of Araneus ventricosus' spider dragline silk using a suspended microdevice. The thermal conductivity of the silk fiber was approximately 0.4WmK at room temperature and gradually increased with an increasing temperature in a manner similar to that of other disordered crystals or proteins.

A vanadium-doped ZnO nanosheets-polymer composite for flexible piezoelectric nanogenerators.

We report high performance flexible piezoelectric nanogenerators (PENGs) by employing vanadium (V)-doped ZnO nanosheets (NSs) and the polydimethylsiloxane (PDMS) composite structure. The V-doped ZnO NSs were synthesized to overcome the inherently low piezoelectric properties of intrinsic ZnO. Ferroelectric phase transition induced in the V-doped ZnO NSs contributed to significantly improve the performance of the PENGs after the poling process.

Computational Study on the Thermal Effects of Implantable Magnetic Stimulation Based on Planar Coils.

Goal: Micromagnetic stimulation using coils sufficiently small to be implanted has been suggested as a potential method to overcome the limitations of electrical stimulation. We investigated the temperature increases in the brain implanted with planar coils.

Methods: We conducted computational simulations on the thermal effects of implantable magnetic stimulation in a brain model using finite-element analysis, by varying geometric parameters of planar spiral coils, and repetitive stimulation pulse patterns.

A microfluidic device for label-free detection of Escherichia coli in drinking water using positive dielectrophoretic focusing, capturing, and impedance measurement.

While sensors that allow for high-throughput enumeration of microorganisms within drinking water are useful for water quality monitoring, it is particularly challenging to accurately quantify microorganisms that are present in low numbers (<100 CFU/mL) in a high-throughput manner. Negative dielectrophoresis (nDEP) is typically utilized in DEP-based cell focusing methods; however, due to its low conductivity, drinking water cannot be analyzed by this approach. Here, we report a positive DEP (pDEP)-based Escherichia coli detection system that is integrated with a focusing and sensing electrode.

Lithium-doped zinc oxide nanowires-polymer composite for high performance flexible piezoelectric nanogenerator.

We present a method to develop high performance flexible piezoelectric nanogenerators (NGs) by employing Li-doped ZnO nanowires (NWs). We synthesized Li-doped ZnO NWs and adopted them to replace intrinsic ZnO NWs with a relatively low piezoelectric coefficient. When we exploited the ferroelectric phase transition induced in Li-doped ZnO NWs, the performance of the NGs was significantly improved and the NG fabrication process was greatly simplified.

Two-dimensional phonon transport in supported graphene.

The reported thermal conductivity (kappa) of suspended graphene, 3000 to 5000 watts per meter per kelvin, exceeds that of diamond and graphite. Thus, graphene can be useful in solving heat dissipation problems such as those in nanoelectronics. However, contact with a substrate could affect the thermal transport properties of graphene.