Reduced interface effect of proton beam irradiation on the electrical properties of WSe2/hBN field effect transistors.

Two-dimensional transition metal dichalcogenide (TMDC) semiconductors are emerging as strong contenders for electronic devices that can be used in highly radioactive environments such as outer space where conventional silicon-based devices exhibit nonideal characteristics for such applications. To address the radiation-induced interface effects of TMDC-based electronic devices, we studied high-energy proton beam irradiation effects on the electrical properties of field-effect transistors (FETs) made with tungsten diselenide (WSe2) channels and hexagonal boron-nitride (hBN)/SiO2gate dielectrics. The electrical characteristics of WSe2FETs were measured before and after the irradiation at various proton beam doses of 1013, 1014, and 1015cm-2. In particular, we demonstrated the dependence of proton irradiation-induced effects on hBN layer thickness in WSe2FETs. We observed that the hBN layer reduces the WSe2/dielectric interface effect which would shift the transfer curve of the FET toward the positive direction of the gate voltage. Also, this interface effect was significantly suppressed when a thicker hBN layer was used. This phenomenon can be explained by the fact that the physical separation of the WSe2channel and SiO2dielectric by the hBN interlayer prevents the interface effects originating from the irradiation-induced positive trapped charges in SiO2reaching the interface. This work will help improve our understanding of the interface effect of high-energy irradiation on TMDC-based nanoelectronic devices.

Quantitative Understanding of Ionic Channel Network Variation in Nafion with Hydration Using Current Sensing Atomic Force Microscopy.

Proton exchange membranes are an essential component of proton-exchange membrane fuel cells (PEMFC). Their performance is directly related to the development of ionic channel networks through hydration. Current sensing atomic force microscopy (CSAFM) can map the local conductance and morphology of a sample surface with sub-nano resolution simultaneously by applying a bias voltage between the conducting tip and sample holder. In this study, the ionic channel network variation of Nafion by hydration has been quantitatively characterized based on the basic principles of electrodynamics and CSAFM. A nano-sized PEMFC has been created using a Pt-coated tip of CSAFM and one side Pt-coated Nafion, and studied under different relative humidity (RH) conditions. The results have been systematically analyzed. First, the morphology of PEMFC under each RH has been studied using line profile and surface roughness. Second, the CSAFM image has been analyzed statistically through the peak value and full-width half-maximum of the histograms. Third, the number of protons moving through the ionic channel network (NPMI) has been derived and used to understand ionic channel network variation by hydration. This study develops a quantitative method to comprehend variations in the ionic channel network by calculating the movement of protons into the ionic channel network based on CSAFM images. To verify the method, a comparison is made between the NPMI and the changes in proton conductivity under different RH conditions and it reveals a good agreement. This developed method can offer a quantitative approach for characterizing the morphological structure of PEM. Also, it can provide a quantitative tool for interpretating CSAFM images.

The North Equatorial Current and rapid intensification of super typhoons.

Super Typhoon Mangkhut, which traversed the North Equatorial Current (NEC; 8-17 °N) in the western North Pacific in 2018, was the most intense Category-5 tropical cyclone (TC) with the longest duration in history-3.5 days. Here we show that the combination of two factors-high ocean heat content (OHC) and increased stratification - makes the NEC region the most favored area for a rapid intensification (RI) of super typhoons, instead of the Eddy Rich Zone (17-25 °N), which was considered the most relevant for RI occurrence. The high OHC results from a northward deepening thermocline in geostrophic balance with the westward-flowing NEC. The stratification is derived from precipitation associated with the Inter-Tropical Convergence Zone in the summer peak typhoon season. These factors, which are increasingly significant over the past four decades, impede the TC-induced sea surface cooling, thus enhancing RI of TCs and simultaneously maintaining super typhoons over the NEC region.

Vitamin C-induced CO2 capture enables high-rate ethylene production in CO2 electroreduction.

High-rate production of multicarbon chemicals via the electrochemical CO2 reduction can be achieved by efficient CO2 mass transport. A key challenge for C-C coupling in high-current-density CO2 reduction is how to promote *CO formation and dimerization. Here, we report molecularly enhanced CO2-to-*CO conversion and *CO dimerization for high-rate ethylene production. Nanoconfinement of ascorbic acid by graphene quantum dots enables immobilization and redox reversibility of ascorbic acid in heterogeneous electrocatalysts. Cu nanowire with ascorbic acid nanoconfined by graphene quantum dots (cAA-CuNW) demonstrates high-rate ethylene production with a Faradaic efficiency of 60.7% and a partial current density of 539 mA/cm2, a 2.9-fold improvement over that of pristine CuNW. Furthermore, under low CO2 ratio of 33%, cAA-CuNW still exhibits efficient ethylene production with a Faradaic efficiency of 41.8%. We find that cAA-CuNW increases *CO coverage and optimizes the *CO binding mode ensemble between atop and bridge for efficient C-C coupling. A mechanistic study reveals that ascorbic acid can facilitate *CO formation and dimerization by favorable electron and proton transfer with strong hydrogen bonding.

Low-Temperature Cross-Linkable Hole Transport Materials for Solution-Processed Quantum Dot and Organic Light-Emitting Diodes with High Efficiency and Color Purity.

Cross-linkable hole transport materials (HTMs) are ideal for improving the performance of solution-processed quantum dot light-emitting diodes (QLEDs) and phosphorescent light-emitting diodes (OLEDs). However, previously developed cross-linkable HTMs possessed poor hole transport properties, high cross-linking temperatures, and long curing times. To achieve efficient cross-linkable HTMs with high mobility, low cross-linking temperature, and short curing time, we designed and synthesized a series of low-temperature cross-linkable HTMs comprising dibenzofuran (DBF) and 4-divinyltriphenylamine (TPA) segments for highly efficient solution-processed QLEDs and OLEDs. The introduction of divinyl-functionalized TPA in various positions of the DBF core remarkably affected their chemical, physical, and electrochemical properties. In particular, cross-linked 4-(dibenzo[b,d]furan-3-yl)-N,N-bis(4-vinylphenyl)aniline (3-CDTPA) exhibited a deep highest occupied molecular orbital energy level (5.50 eV), high hole mobility (2.44 × 10-4 cm2 V-1 s-1), low cross-linking temperature (150 °C), and short curing time (30 min). Furthermore, a green QLED with 3-CDTPA as the hole transport layer (HTL) exhibited a notable maximum external quantum efficiency (EQEmax) of 18.59% with a remarkable maximum current efficiency (CEmax) of 78.48 cd A-1. In addition, solution-processed green OLEDs with 3-CDTPA showed excellent device performance with an EQEmax of 15.61%, a CEmax of 52.51 cd A-1, and outstanding CIE(x, y) color coordinates of (0.29, 0.61). This is one of the highest reported EQEs and CEs with high color purity for green solution-processed QLEDs and OLEDs using a divinyl-functionalized cross-linked HTM as the HTL. We believe that this study provides a new strategy for designing and synthesizing practical cross-linakable HTMs with enhanced performance for highly efficient solution-processed QLEDs and OLEDs.

Quantitative Study of Charge Distribution Variations on Silica-Nafion Composite Membranes under Hydration Using an Approximation Model.

Understanding the ionic structure and charge transport on proton exchange membranes (PEMs) is crucial for their characterization and development. Electrostatic force microscopy (EFM) is one of the best tools for studying the ionic structure and charge transport on PEMs. In using EFM to study PEMs, an analytical approximation model is required for the interoperation of the EFM signal. In this study, we quantitatively analyzed recast Nafion and silica-Nafion composite membranes using the derived mathematical approximation model. The study was conducted in several steps. In the first step, the mathematical approximation model was derived using the principles of electromagnetism and EFM and the chemical structure of PEM. In the second step, the phase map and charge distribution map on the PEM were simultaneously derived using atomic force microscopy. In the final step, the charge distribution maps of the membranes were characterized using the model. There are several remarkable results in this study. First, the model was accurately derived as two independent terms. Each term shows the electrostatic force due to the induced charge of the dielectric surface and the free charge on the surface. Second, the local dielectric property and surface charge are numerically calculated on the membranes, and the calculation results are approximately valid compared with those in other studies.

High-Quality Microprintable and Stretchable Conductors for High-Performance 5G Wireless Communication.

With the advent of 5G wireless and Internet of Things technologies, flexible and stretchable printed circuit boards (PCBs) should be designed to address all the specifications necessary to receive signal transmissions, maintaining the signal integrity, and providing electrical connections. Here, we propose a silver nanoparticle (AgNP)/silver nanowire (AgNW) hybrid conductor and high-quality microprinting technology for fabricating flexible and stretchable PCBs in high-performance 5G wireless communication. A simple and low-cost reverse offset printing technique using a commercial adhesive hand-roller was adapted to ensure high-resolution and excellent pattern quality. The AgNP/AgNW micropatterns were fabricated in various line widths, from 5 µm to 5 mm. They exhibited excellent pattern qualities, such as fine line spacing, clear edge definition and outstanding pattern uniformity. After annealing via intense pulsed light irradiation, they showed outstanding electrical resistivity (15.7 µΩ cm). Moreover, they could withstand stretching up to a strain of 90% with a small change in resistance. As a demonstration of their practical application, the AgNP/AgNW micropatterns were used to fabricate 5G communication antennas that exhibited excellent wireless signal processing at operating frequencies in the C-band (4-8 GHz). Finally, a wearable sensor fabricated with these AgNP/AgNW micropatterns could successfully detected fine finger movements in real time with excellent sensitivity.

Analysis of Ionic Domain Evolution on a Nafion-Sulfonated Silica Composite Membrane Using a Numerical Approximation Model Based on Electrostatic Force Microscopy.

It is important to characterize the proton transport mechanisms of proton exchange membranes (PEMs). Electrostatic force microscopy (EFM) is used to characterize the ionic structures of membranes. In this study, we attempted to quantitatively analyze the proton conductivity enhancement of Nafion-sulfonated silica (SSA) composite membranes with variations in the ionic channel distribution. This study involved several steps. The morphology and surface charge distribution of both membranes were measured using EFM. The measured data were analyzed using a numerical approximation model (NAM) that was capable of providing the magnitude and classification of the surface charges. There were several findings of ionic channel distribution variations in Nafion-SSA. First, the mean local ionic channel density of Nafion-SSA was twice as large as that of the pristine Nafion. The local ionic channel density was non-uniform and the distribution of the ionic channel density of Nafion-SSA was 23.5 times larger than that of pristine Nafion. Second, local agglomerations due to SSA were presumed by using the NAM, appearing in approximately 10% of the scanned area. These findings are meaningful in characterizing the proton conductivity of PEMs and imply that the NAM is a suitable tool for the quantitative assessment of PEMs.

Reduced dopant-induced scattering in remote charge-transfer-doped MoS2 field-effect transistors.

Efficient doping for modulating electrical properties of two-dimensional (2D) transition metal dichalcogenide (TMDC) semiconductors is essential for meeting the versatile requirements for future electronic and optoelectronic devices. Because doping of semiconductors, including TMDCs, typically involves generation of charged dopants that hinder charge transport, tackling Coulomb scattering induced by the externally introduced dopants remains a key challenge in achieving ultrahigh mobility 2D semiconductor systems. In this study, we demonstrated remote charge transfer doping by simply inserting a hexagonal boron nitride layer between MoS2 and solution-deposited n-type dopants, benzyl viologen. A quantitative analysis of temperature-dependent charge transport in remotely doped devices supports an effective suppression of the dopant-induced scattering relative to the conventional direct doping method. Our mechanistic investigation of the remote doping method promotes the charge transfer strategy as a promising method for material-level tailoring of electrical and optoelectronic devices based on TMDCs.

High-performance biosensor using a sandwich assay via antibody-conjugated gold nanoparticles and fiber-optic localized surface plasmon resonance.

For real-time and high-sensitivity analysis of low-concentration targets, a sandwich immunoassay using second antibody-second gold nanoparticle (2nd Ab-2nd AuNP) conjugates was combined with fiber-optic localized surface plasmon resonance (FO LSPR). An FO LSPR format was constructed by immobilizing AuNPs on a fiber-optic cross-section for compactness, portability, and ease of handling. In addition, it was combined with a microfluidic system to ensure reproducibility and reliability of measurements. A detection limit of 97.6 fg/mL (148 aM) was obtained for thyroglobulin (Tg) without a sandwich assay. The detection limit was enhanced by approximately 15 times (6.6 fg/mL, 10 aM) when a sandwich strategy was performed with a 2nd Ab-2nd AuNP signal amplifier to further improve the responsivity. Additionally, the good selectivity of the proposed method was confirmed against the unpaired antigen. To evaluate its practical applicability in the field, an FO LSPR biosensor boosted with a sandwich assay using antibody-functionalized AuNPs was applied to detect Tg contained in patient serum, and the results were compared and verified with those of a commercial radioimmunoassay kit. Based on the above results, the signal-enhancing immunoassay with FO LSPR will contribute to the development of optical biosensors for early diagnosis and preventive applications.

Fiber Optic Plasmonic Sensors Based on Nanodome Arrays with Nanogaps.

In this study, a high-performance fiber optic surface plasmon resonance (FO-SPR) sensor using a dome array with nanogaps (DANG) is proposed for label-free real-time detection of biomolecules. A novel and simple method using polymer beads enables high sensitivity by allowing hotspots with nanometer spacing between the Au dome and the surrounding film. The nanodome structure, which comprises a polymer core and a Au shell, induces a localized surface plasmon, expands the sensing area, and extensively enhances the electromagnetic field. The refractive index sensitivity of the FO-SPR sensor with nanostructures, i.e., with nanogaps and nanodomes, was found to be 7.8 times higher than that of the FO-SPR sensor without nanostructures. The proposed sensor achieved a low detection limit of 38 fg/mL while quantifying thyroglobulin antibody-antigen interactions and exhibited excellent selectivity. In addition, it helped detect serum samples with a 103% recovery rate.

Proton irradiation effects on mechanochemically synthesized and flash-evaporated hybrid organic-inorganic lead halide perovskites.

A hybrid organic-inorganic halide perovskite is a promising material for developing efficient solar cell devices, with potential applications in space science. In this study, we synthesized methylammonium lead iodide (MAPbI3) perovskites via two methods: mechanochemical synthesis and flash evaporation. We irradiated these perovskites with highly energetic 10 MeV proton-beam doses of 1011, 1012, 1013, and 4 × 1013protons cm-2and examined the proton irradiation effects on the physical properties of MAPbI3perovskites. The physical properties of the mechanochemically synthesized MAPbI3perovskites were not considerably affected after proton irradiation. However, the flash-evaporated MAPbI3perovskites showed a new peak in x-ray diffraction and an increased fluorescence lifetime in time-resolved photoluminescence under high-dose conditions, indicating considerable changes in their physical properties. This difference in behavior between MAPbI3perovskites synthesized via the abovementioned two methods may be attributed to differences in radiation hardness associated with the bonding strength of the constituents, particularly Pb-I bonds. Our study will help to understand the radiation effect of proton beams on organometallic halide perovskite materials.

Design and validation of fiber optic localized surface plasmon resonance sensor for thyroglobulin immunoassay with high sensitivity and rapid detection.

A simple optical fiber sensor based on localized surface plasmon resonance was constructed for direct and rapid measurement of thyroglobulin (Tg). Specific tests for Tg in patients that have undergone thyroidectomy are limited because of insufficient sensitivity, complicated procedures, and in some cases, a long time to yield a result. A sensitive, fast, and simple method is necessary to relieve the psychological and physical burden of the patient. Various concentrations of Tg were measured in a microfluidic channel using an optical fiber sensor with gold nanoparticles. The sensor chip has a detection limit of 93.11 fg/mL with no specificity for other antigens. The potential applicability of the Tg sensing system was evaluated using arbitrary samples containing specific concentrations of Tg. Finally, the sensor can be employed to detect Tg in the patient's serum, with a good correlation when compared with the commercial kit.

Fabrication and measurement of fiber optic localized surface plasmon resonance sensor based on gold nanoparticle dimer.

Fiber optic localized surface plasmon resonance (FO LSPR) sensors capable of portable, real-time, and remote sensing are emerging with the progress of lab-on-fiber technology. However, the small area of the substrate by the optical fiber often restricts the sensitivity of the FO LSPR sensors. To improve the performance of the FO LSPR sensors, it is necessary to enhance the interactions between incident light and plasmonic nanostructures within a defined region. Dimer in which two nanoparticles are arranged with nanometer spacing can effectively increase the light-nanostructure interactions. It is well known that the nanogap made in the assembled nanoparticles significantly enhances the intensity of the electromagnetic field in the confined area by the hot spot effect. We fabricate the dimers of gold nanoparticles on the optical fiber with benzenethiol using a method that reduces the repulsive force between the nanoparticles. In the dimers, the strong plasmonic interaction between the two nanoparticles produces a longitudinal plasmon coupling band, which is compared to the transverse plasmon band by the monomer-based FO LSPR sensor with a similar density of gold nanoparticles. In the proposed sensor, the longitudinal band displays approximately 9.1 times improved sensitivity. When two types of sensors are applied to the biosensor application, the dimer-based FO LSPR sensor also proves an improved limit of detection of about 2.6 times. This method is expected to become a milestone in the field of measurement for small molecules and low concentration through the advancement of the yield and density of dimers.

Multivalent Nanosheet Antibody Mimics for Selective Microbial Recognition and Inactivation.

Antibodies are widely used as recognition elements in sensing and therapy, but they suffer from poor stability, long discovery time, and high cost. Herein, a facile approach to create antibody mimics with flexible recognition phases and luminescent rigid scaffolds for the selective recognition, detection, and inactivation of pathogenic bacteria is reported. Tripeptides with a nitriloacetate-Cu group are spontaneously assembled on transition metal dichalcogenide (TMD) nanosheets via coordination bonding, providing a diversity of TMD-tripeptide assembly (TPA) antibody mimics. TMD-TPA antibody mimics can selectively recognize various pathogenic bacteria with nanomolar affinities. The bacterial binding sites for TMD-TPA are identified by experiments and molecular dynamics simulations, revealing that the dynamic and multivalent interactions of artificial antibodies play a crucial role for their recognition selectivity and affinity. The artificial antibodies allow the rapid and selective detection of pathogenic bacteria at single copy in human serum and urine, and their effective inactivation for therapy of infected mice. This work demonstrates the potential of TMD-TPA antibody mimics as an alternative to natural antibodies for sensing and therapy.

Majority Voting-Based MAC Protocol for Exploiting Link-Layer Diversity in Wireless Networks.

In wireless local area networks (WLANs), the effect of interference signals between neighboring nodes increases as the number of wireless nodes using limited radio frequency resources in a limited space increases, which can significantly degrade the reliability of data transmission. In high-density WLANs, there can be several neighboring access points (APs) that can receive uplink transmission from a station. In conventional medium access control (MAC) protocols, uplink data frames containing errors or transmitted from a non-associated station are discarded at APs. Alternatively, we propose a MAC protocol using redundant wireless links between neighboring APs and the non-associated stations. In the proposed MAC protocol, we consider a centralized WLAN with a control node that performs error corrections of erroneous uplink data frames via a majority voting algorithm-based link-layer diversity scheme using uplink data received from multiple APs to increase the reliability of data transmission. In addition, we propose an adaptive carrier sensing ranging mechanism to improve the uplink network throughput in the proposed centralized WLAN system. Further, we conduct simulation studies and software-defined radio-based experiments to evaluate the performance of the proposed MAC protocol in various WLAN scenarios.

Analysis of Ionic Domains on a Proton Exchange Membrane Using a Numerical Approximation Model Based on Electrostatic Force Microscopy.

Understanding the ionic channel network of proton exchange membranes that dictate fuel cell performance is crucial when developing proton exchange membrane fuel cells. However, it is difficult to characterize this network because of the complicated nanostructure and structure changes that depend on water uptake. Electrostatic force microscopy (EFM) can map surface charge distribution with nano-spatial resolution by measuring the electrostatic force between a vibrating conductive tip and a charged surface under an applied voltage. Herein, the ionic channel network of a proton exchange membrane is analyzed using EFM. A mathematical approximation model of the ionic channel network is derived from the principle of EFM. This model focusses on free charge movement on the membrane based on the force gradient variation between the tip and the membrane surface. To verify the numerical approximation model, the phase lag of dry and wet Nafion is measured with stepwise changes to the bias voltage. Based on the model, the variations in the ionic channel network of Nafion with different amounts of water uptake are analyzed numerically. The mean surface charge density of both membranes, which is related to the ionic channel network, is calculated using the model. The difference between the mean surface charge of the dry and wet membranes is consistent with the variation in their proton conductivity.

Design optimization of a 6.4†mm-diameter electromagnetic 2D scanning micromirror.

We present the design optimization, fabrication, and analysis of an electromagnetic biaxial scanning micromirror with 6.4 mm-diameter. The scanner is composed of a micromirror supported by two concentric gimbal structures with unique single turn coil. A cylindrical permanent magnet assembly is placed under the micromirror to provide a radial magnetic field for actuation. Lumped element model parameters and magnetic circuit have been optimized to maximize the driving torque. Fabricated micromirror has been actuated at 300 Hz and 1,010 Hz and maximum optical scan angle of 25.6° and 35.3° have been obtained for the vertical and horizontal scans, respectively. Crosstalk during the actuation has been analyzed, and improved models have been proposed to reduce the crosstalk.

Fiber optic sensor based on ZnO nanowires decorated by Au nanoparticles for improved plasmonic biosensor.

Fiber-optic-based localized surface plasmon resonance (FO-LSPR) sensors with three-dimensional (3D) nanostructures have been developed. These sensors were fabricated using zinc oxide (ZnO) nanowires and gold nanoparticles (AuNPs) for highly sensitive plasmonic biosensing. The main achievements in the development of the biosensors include: (1) an extended sensing area, (2) light trapping effect by nanowires, and (3) a simple optical system based on an optical fiber. The 3D nanostructure was fabricated by growing the ZnO nanowires on the cross-section of optical fibers using hydrothermal synthesis and via immobilization of AuNPs on the nanowires. The proposed sensor outputted a linear response according to refractive index changes. The 3D FO-LSPR sensor exhibited an enhanced localized surface plasmon resonance response of 171% for bulk refractive index changes when compared to the two-dimensional (2D) FO-LSPR sensors where the AuNPs are fixed on optical fiber as a monolayer. In addition, the prostate-specific antigen known as a useful biomarker to diagnose prostate cancer was measured with various concentrations in 2D and 3D FO-LSPR sensors, and the limits of detection (LODs) were 2.06 and 0.51 pg/ml, respectively. When compared to the 2D nanostructure, the LOD of the sensor with 3D nanostructure was increased by 404%.

A Low Frequency Vibration Energy Harvester Using ZnO Nanowires on Elastic Interdigitated Electrodes.

This paper presents a low frequency piezoelectric vibration energy harvester using ZnO nanowires on elastic interdigitated electrodes. The interdigitated electrodes are formed using electroplated Ni and have suspended parts at the edges that are elastic and deformable by applying external force. A spherical Ni ball is used as a proof mass, which transforms a low frequency mechanical vibration into the force applied to deform the elastic electrodes. The ZnO nanowires are grown selectively on the electrodes and can generate a piezoelectric potential when the elastic electrodes are deformed by the proof mass activated by the external mechanical vibration. The proposed operation concept is demonstrated using two different types of energy harvesters, which have simple suspended part and cantilever array structures added to the electrodes, respectively. The output voltage of the fabricated harvesters is measured using a vibration exciter at 6 Hz sinusoidal vibration with an acceleration of 0.5 g. Maximum output power of 12.8 pW and 18.8 pW was generated with a load resistance of 1 MΩ for the harvesters using the simple suspended structure and cantilever array, respectively.