Carrier Trap and Their Effects on the Surface and Core of AlGaN/GaN Nanowire Wrap-Gate Transistor.

We used capacitance-voltage (C-V), conductance-voltage (G-V), and noise measurements to examine the carrier trap mechanisms at the surface/core of an AlGaN/GaN nanowire wrap-gate transistor (WGT). When the frequency is increased, the predicted surface trap density promptly drops, with values ranging from 9.1 × 1013 eV-1∙cm-2 at 1 kHz to 1.2 × 1011 eV-1∙cm-2 at 1 MHz. The power spectral density exhibits 1/f-noise behavior in the barrier accumulation area and rises with gate bias, according to the 1/f-noise features. At lower frequencies, the device exhibits 1/f-noise behavior, while beyond 1 kHz, it exhibits 1/f2-noise behavior. Additionally, when the fabricated device governs in the deep-subthreshold regime, the cutoff frequency for the 1/f2-noise features moves to the subordinated frequency (~102 Hz) side.

Inactivation of Escherichia coli O157: H7 in foods by emerging technologies: a review.

Escherichia coli O157: H7 is a representative foodborne pathogen that causes haemorrhagic colitis, bloody diarrhea, and fatal haemolytic uraemic syndrome. Previously, only conventional heat treatment was used to pasteurised food; however, this method decreases food quality, including colour change, denatures proteins, and causes lipid oxidation. Therefore, emerging technologies to inactivate pathogens in food that affect food quality minimally have been researched and developed. This review aims to compile research since 2018 and briefly describe the inactivation mechanisms of emerging technologies such as microwave, radio frequency, ohmic heating, superheated steam, ionising radiation (gamma irradiation, electron beam, and X-rays), high pressure, ultraviolet light, pulsed light, ultrasound, gas treatment, plasma, and combination treatments. Pulsed electric field and electrolysed water were excluded because few research papers were published after 2018. In addition, the shortcomings of emerging technologies in the control of E. coli O157: H7 and the directions for emerging technology research are presented. Taking advantage of emerging technologies with many benefits will significantly improve food safety.

Viscosity-Controllable Graphene Oxide Colloids Using Electrophoretically Deposited Graphene Oxide Sheets.

Graphene oxide (GO) is one of the interesting ink materials owing to its fascinating properties, such as high dissolubility in water and high controllable electric properties. For versatile printing application, the viscosity of GO colloids should be controlled in order to meet the specific process requirements. Here, we report on the relatively rapid fabrication of viscosity-increased GO (VIGO) colloids mixed with electrophoretically deposited GO sheets (EPD-GO). As the GO colloid concentration, applied voltage, and deposition time increase, the viscosity of the GO colloids becomes high. The reason for the improved viscosity of GO colloids is because EPD-GO has parallel stacked GO sheets. The GO and VIGO colloids are compared and characterized using various chemical and structural analyzers. Consequently, our simple and fast method for the fabrication of GO colloids with enhanced viscosity can be used for producing inks for flexible and printed electronics.

Evaporation-Rate Control of Water Droplets on Flexible Transparent Heater for Sensor Application.

To develop high-performance de- or anti-frosting/icing devices based on transparent heaters, it is necessary to study the evaporation-rate control of droplets on heater surfaces. However, almost no research has been done on the evaporation-rate control of liquid droplets on transparent heaters. In this study, we investigate the evaporation characteristics of water droplets on transparent heater surfaces and determine that they depend upon the surface wettability, by modifying which, the complete evaporation time can be controlled. In addition, we study the defrosting and deicing performances through the surface wettability, by placing the flexible transparent heater on a webcam. The obtained results can be used as fundamental data for the transparent defrosting and deicing systems of closed-circuit television (CCTV) camera lenses, smart windows, vehicle backup cameras, aircraft windows, and sensor applications.

Moisture Effect on Particulate Matter Filtration Performance using Electro-Spun Nanofibers including Density Functional Theory Analysis.

In this study, we use density functional theory (DFT) calculations to investigate the effect of moisture on the performance of three types of nanofiber (NF)-based air-filter media prepared by electrospinning polyvinyl alcohol, polyvinylidene fluoride, and polyacrylonitrile (PAN). Based on the DFT calculations of the intermolecular interactions between the NF-based filter media and water molecules, the PAN-NF filter is expected to exhibit the best performance in the wet state. Experiment studies also successfully demonstrate that the PAN-NF filter medium has better performance in the filtration of particulate matter (PM) than a commercial semi-high efficiency particulate air filter under wet conditions, and these results are in good agreement with the DFT calculation. The PAN-NF filter shows better performance because of its hydrophilic nature and the relatively low thickness the filter medium that allowed fast recovery of its PM-filtration performance.

Spontaneous Additive Nanopatterning from Solution Route Using Selective Wetting.

Nanopatterns of functional materials have successfully led innovations in a wide range of fields, but further exploration of their full potential has often been limited because of complex and cost-inefficient patterning processes. We here propose an additive nanopatterning process of functional materials from solution route using selective wetting phenomenon. The proposed process can produce nanopatterns as narrow as 150 nm with high yield over large area at ultrahigh process speed, that is, the speed of solution dragging, of up to ca. 4.6 m·min-1. The process is highly versatile that it can utilize a wide range of solution materials, control vertical structures including pattern thickness and multistacks, and produce nanopatterns on various substrates with emerging form factors such as foldability and disposability. The solution patterning in nanoscale by selective wetting is enabled by corresponding surface energy patterns in high contrast that are achieved by one-step imprinting onto hydrophobic/hydrophilic bilayers. The mechanisms and control parameters for the solution patterning are revealed by fluid-dynamic simulation. With the aforementioned advantages, we demonstrate 25 400 pixel-per-inch light-emitting pixel arrays and a plasmonic color filter of 10 cm × 10 cm area on a plastic substrate as potential applications.

Controlled Patterning of Vertical Silicon Structures Using Polymer Lithography and Wet Chemical Etching.

In order to improve their performance for various applications, a facile method for the wafer-scale fabrication of micro/nano-patterned vertical silicon (Si) structures such as silicon nanowires (SiNWs), silicon nanorods (SiNRs), and porous silicon (p-Si) was developed. The method is based on the combination of lithography techniques (photolithography, thermal nano-imprint lithography, nanosphere lithography) and wet chemical etching (electro-chemical etching, metal-assisted chemical etching) processes. Micro-patterned p-Si with various pore diameters from 30 nm to 1.2 um were fabricated via electro-chemical etching. Micro/nano-patterned Si microstructures, nanorods, and nanowires were also successfully fabricated by changing the thickness of the metal layer of 5 nm or 20 nm in the metal-assisted chemical etching process. This study also investigated the effect of the etching time and patterning on the etched SiNWs length. This method provides advantages of simplicity, speed, large-scale production, easy size and shape manipulation, and low cost.

A facile patterning of silver nanowires using a magnetic printing method.

Patterning of metal nanowires (NWs) is vital for the fabrication of NW-based, high-performance devices such as sensors, transparent conducting electrodes, and optoelectronics. However, the majority of existing patterning methods require complex and expensive technologies. For this reason, we report for the first time a facile and quick patterning method of silver (Ag) NWs using a magnetic printing method. We successfully demonstrated a patterned AgNW grid structure ona flexible substrate as transparent electrodes. The flexible AgNW grid electrode exhibited optical and electrical properties comparable to those of commercial transparent conducting electrodes.We believe our work will be broadly applicable to other NW-based devices such as sensors,energy storage devices, meta devices, nanoscale electronics, and optoelectronics.

13.2% efficiency Si nanowire/PEDOT:PSS hybrid solar cell using a transfer-imprinted Au mesh electrode.

In recent years, inorganic/organic hybrid solar cell concept has received growing attention for alternative energy solution because of the potential for facile and low-cost fabrication and high efficiency. Here, we report highly efficient hybrid solar cells based on silicon nanowires (SiNWs) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT: PSS) using transfer-imprinted metal mesh front electrodes. Such a structure increases the optical absorption and shortens the carrier transport distance, thus, it greatly increases the charge carrier collection efficiency. Compared with hybrid cells formed using indium tin oxide (ITO) electrodes, we find an increase in power conversion efficiency from 5.95% to 13.2%, which is attributed to improvements in both the electrical and optical properties of the Au mesh electrode. Our fabrication strategy for metal mesh electrode is suitable for the large-scale fabrication of flexible transparent electrodes, paving the way towards low-cost, high-efficiency, flexible solar cells.

Rapid Low-Temperature 3D Integration of Silicon Nanowires on Flexible Substrates.

The vertical integration of 1D nanostructures onto the 2D substrates has the potential to offer significant performance gains to flexible electronic devices due to high integration density, large surface area, and improved light absorption and trapping. A simple, rapid, and low temperature transfer bonding method has been developed for this purpose. Ultrasonic vibration is used to achieve a low temperature bonding within a few seconds, resulting in a polymer-matrix-free, electrically conducting vertical assembly of silicon nanowires (SiNWs) with a graphene/PET substrate. The microscopic structure, and mechanical and electrical characteristics of the interface between the transferred SiNW array and graphene layer are subsequently investigated, revealing that this creates a mechanically robust and electrically Ohmic contact. This newly developed ultrasonic transfer bonding technique is also found to be readily adaptable for diverse substrates of both metal and polymer. It is therefore considered as a valuable technique for integrating 1D vertical nanostructures onto the 2D flexible substrates for flexible photovoltaics, energy storage, and water splitting systems.

High-durable AgNi nanomesh film for a transparent conducting electrode.

Uniform metal nanomesh structures are promising candidates that may replace of indium-tin oxide (ITO) in transparent conducting electrodes (TCEs). However, the durability of the uniform metal mesh has not yet been studied. For this reason, a comparative analysis of the durability of TCEs based on pure Ag and AgNi nanomesh, which are fabricated by using simple transfer printing, is performed. The AgNi nanomesh shows high long-term stability to oxidation, heat, and chemicals compared with that of pure Ag nanomesh. This is because of nickel in the AgNi nanomesh. Furthermore, the AgNi nanomesh shows strong adhesion to a transparent substrate and good stability after repeated bending.

Polymer-free Vertical Transfer of Silicon Nanowires and their Application to Energy Storage.

Silicon nanowires (SiNWs) for use as lithium-ion battery (LIB) anode materials have been studied for their one-dimensional (1D) properties and ability to accommodate large volume changes and avoid rapid capacity fading during cycling. Although the vertical transfer of SiNWs from their original substrate onto a conducting electrode is very important, to date, there has been no report of a direct integration method without polymer binders. Here, we propose for the first time a vertical transfer method for SiNWs grown on a Si substrate directly to the current-collecting electrode without using a polymer adhesive for the use as a binder-free LIB anode. The vertical SiNWs produced using a low-cost wafer-scale metal-assisted chemical etching (MaCE) process have been successfully transferred directly to a copper electrode coated with a thin Ag layer by using a simple hot pressing method. When evaluated as an LIB anode without using conventional polymeric binder and a conducting additive, the transferred vertically aligned SiNWs showed a high specific capacity (≈2150 mAh g(-1) ) and excellent rate performance. It is believed that the anode-manufacturing process is simple and fast, thus enabling a large-scale production that is of low-cost, broadly applicable, and provides new avenues for the rational engineering of Si-based electrode materials with enhanced power density and conductivity.

Highly robust silicon nanowire/graphene core-shell electrodes without polymeric binders.

A large theoretical charge storage capacity along with a low discharge working potential renders silicon a promising anode material for high energy density lithium ion batteries. However, up to 400% volume expansion during charge-discharge cycling coupled with a low intrinsic electronic conductivity causes pulverization and fracture, thus inhibiting silicon's widespread use in practical applications. We report herein on a low cost approach to fabricate hybrid silicon nanowire (SiNW)/graphene nanostructures that exhibit enhanced cycle performance with the capability of retaining more than 90% of their initial capacity after 50 cycles. We also demonstrate the use of hot-pressing in the absence of any common polymer binder such as PVDF to bind the hybrid structure to the current collector. The applied heat and pressure ensure strong adhesion between the SiNW/graphene nano-composite and current collector. This facile yet strong binding method is expected to find use in the further development of polymer-binder free anodes for lithium ion batteries.

Superamphiphobic surface by nanotransfer molding and isotropic etching.

We present a novel method of fabricating superhydrophobic and superoleophobic surfaces with nanoscale reentrant curvature by nanotransfer molding and controlled wet etching of the facile undercut. This method produces completely ordered re-entrant nanostructures and prevents capillary-induced bundling effects. The mushroom-like, re-entrant, overhanging structure demonstrates superhydrophobic and superoleophobic characteristics, as tested by water droplet bouncing and contact angle measurements, and has high transparency on a flexible substrate. Widespread use as self-cleaning surfaces is expected in the near future.

A micro-system based on glass-nanoporous silicon for optical sensing of organic solvent vapor.

We present a recent experimental study on the application of nanoporous silicon (np-Si) to an optical vapor sensor. We fabricated the micro-system based on a glass-nanoporous silicon layer on a p(+)-type silicon wafer. To check the selectivity and sensitivity of the np-Si layer to organic vapors, we prepared three types of np-Si layer samples--a single layer, distributed Bragg reflector (DBR) layer, and microcavity layer--and investigated its reflectance spectra upon exposure to different concentrations of various organic vapors. When the np-Si layer samples were exposed to the organic vapors, a red-shift occurred in the reflectance spectrum, and we determined that this red-shift can be attributed to the changes in the refractive index induced by the capillary condensation of the organic vapor within the pores of the np-Si layer. The np-Si layer samples showed excellent sensing ability to different types and concentrations of organic vapors. After removing the organic vapors, the reflectance spectrum immediately returned to its original state.

Nano-engineered optimal templates for surface-plasmon enhanced Raman scattering.

We investigated the critical conditions to realize reliable and nano-engineered templates for surface-plasmon enhanced Raman scattering (SERS). Ultra-sensitive SERSs of thymine oligonucleotides were successfully realized on the template of Au nanoparticle arrays which were prepared by the combination of electron-beam lithography and post-chemical modification techniques. Drastic enhancement of Raman signal from the thymine oligonucleotides was only observed on the optimized templates, where the tuning of the plasmon resonance condition and the formation of the hot spots were both critical. Our results suggest that the artificial generation of reproducible and controlled hot spots can be achieved by our approach.

Clinical approach to the standardization of oriental medical diagnostic pattern identification in stroke patients.

In Korea, many stroke patients receive oriental medical care, in which pattern-identification plays a major role. Pattern-identification is Oriental Medicine's unique diagnostic system. This study attempted to standardize oriental medical pattern-identification for stroke patients. This was a community-based multicenter study that enrolled stroke patients within 30 days after their ictus. We assessed the patients' general characteristics and symptoms related to pattern-identification. Each patient's pattern was determined when two doctors had the same opinion. To determine which variables affect the pattern-identification, binary logistic regression analysis was used with the backward method. A total of 806 stroke patients were enrolled. Among 480 patients who were identified as having a certain pattern, 100 patients exhibited the Fire Heat Pattern, 210 patients the Phlegm Dampness Pattern, nine patients the Blood Stasis Pattern, 110 patients the Qi Deficiency Pattern, and 51 patients the Yin Deficiency Pattern. After the regression analysis, the predictive logistic equations for the Fire Heat, Phlegm Dampness, Qi Deficiency, and Yin Deficiency patterns were determined. The Blood Stasis Pattern was omitted because the sample size was too small. Predictive logistic equations were suggested for four of the patterns. These criteria would be useful in determining each stroke patient's pattern in clinics. However, further studies with large samples are necessary to validate and confirm these criteria.