Wettability of CNW/ITO Micro Structure for Modification of Surface Hydrophilicity

Although the carbon nanowall is a remarkable material in various fields, it generally shows near hydrophobicity. For modification of hydrophilicity, various modification techniques have been utilized, however, most of the techniques adopted a modification to carbon oxide by chemical processing and plasma treatment, which induce carbon lattice defects, causing the decline of the carbon nanowall quality. While we introduce an eco-friendly modification technique that causes non-defect of carbon lattice and maintains intrinsic carbon nanowall properties by depositing ITO on pristine-carbon nanowall for inducing hydrophilicity. The morphology of carbon nanowall (CNW)/ indium tin oxide (ITO) microstructure was examined by FE-SEM, and the functional group and oxygen components of ITO were investigated by analyzing XPS. The contact angles were measured for wettability analysis according to the surface thickness of ITO

Adhesion-Increased Carbon Nanowalls for the Electrodes of Energy Storage Systems

Carbon nanowalls (CNWs), which are used as electrodes for secondary batteries in energy storage systems (ESSs), have the widest reaction surface area among the carbon-based nanomaterials, but their application is rare due to their low adhesion with substrates. Indium tin oxide (ITO), a representative transparent conducting oxide (TCO) material, is widely used as the electrode for displays, solar cells, etc. Titanium nitride (TiN) is a well-used material as an interlayer for improving the adhesion between two materials. In this study, ITO or TiN thin films were used as an interlayer to improve the adhesion between a CNW and a substrate. The interlayer was deposited on the substrate using a radio frequency (RF) magnetron sputtering system with a four-inch TiN or ITO target. CNWs were grown on the interlayer-coated substrate using a microwave-plasma-enhanced chemical vapor deposition (MPECVD) system with a mixture of methane (CH4) and hydrogen (H2) gases. The adhesion of the CNW/interlayer/substrate structure was observed through ultrasonic cleaning

Innovative Method Using Adhesive Force for Surface Micromachining of Carbon Nanowall

The application of a carbon nanowall (CNW) via transfer is very demanding due to the unusual structure of vertically grown wall-shaped that easily collapses. In addition, direct growth on a device cannot obtain a precision-patterned shape because of the temperature limit of the photoresist (PR). Therefore, in this paper, we demonstrate a new CNW surface micromachining technology capable of direct growth. In order to reduce unexpected damage caused by chemical etching, a physical force was used to etch with the adhesive properties of CNWs that have low adhesion to silicon wafer. To prevent compositing with PR, the CNW was surface modified using oxygen plasma. Since there is a risk of surface-modified CNW (SMCNW) collapse in an ultrasonic treatment, which is a physical force, the CNW was coated with PR. After etching the SMCNW grown on PR uncoated area, PR was lifted off using an acetone solution. The effect on the SMCNW by the lift-off process was investigated. The surface, chemical, and structural properties of PR-removed SMCNW and pristine-SMCNW were compared and showed a minimal difference. Therefore, the CNW surface micromachining technique was considered successful

Study of a Carbon Nanowall Synthesized on an MWCNT-Based Buffer Layer for Improvement of Electrical Properties

We conducted experiments to improve the electrical properties of the CNW (carbon nanowall), which has lower electrical properties than other carbon allotropes such as graphene and CNT (carbon nanotube), and report the results through this article. The carbon nanowall has an amorphous buffer layer, leading to low electrical properties, and MWCNT (multi-walled carbon nanotube) was used as a buffer layer to improve this issue, and then a CNW was grown on it by CVD (chemical vapor deposition). Then, the content of MWCNT was adjusted to 30 µL, 50 µL, and 70 µL to analyze the electrical properties accordingly. Alteration in carrier concentration, carrier mobility and resistivity were observed as electrical properties. Dramatic changes in electrical properties with MWCNT content were identified. The ohmic contact state between the MWCNT-based buffer layer and the CNW was investigated by analysis of the I-V and I-R characteristics and the electrical stability according to the linearity of the curve

A Hierarchical Metal Nanowire Network Structure for Durable, Cost-Effective, Stretchable, and Breathable Electronics

Polymer nanofiber-based porous structures ("breathable devices") have been developed for breathable epidermal electrodes, piezoelectric nanogenerators, temperature sensors, and strain sensors, but their applications are limited because increasing the porosity reduces device robustness. Herein, we report an approach to produce ultradurable, cost-effective breathable electronics using a hierarchical metal nanowire network and an optimized photonic sintering process. Photonic sintering significantly reduces the sheet resistance (16.25 to 6.32 ω sq-1) and is 40% more effective than conventional thermal annealing (sheet resistance: 12.99 ω sq-1). The mechanical durability of the sintered (648.9 ω sq-1) sample is notably improved compared to that of the untreated (disconnected) and annealed (19.1 kω sq-1) samples after 10,000 deformation cycles at 40% tensile strain. The sintered sample exhibits ∼29 times less change in electrical performance compared to the thermally annealed sample. This approach will lead to the development of affordable and ultradurable commercial breathable electronics. © 2021 American Chemical Society.FALS

An All-Nanofiber-Based Substrate-Less, Extremely Conformal, and Breathable Organic Field Effect Transistor for Biomedical Applications

Nanofiber-based electronic devices have attracted considerable interest owing to their conformal integration on complicated surfaces, flexibility, and sweat permeability. However, building complicated electronics on nanomesh structure has not been successful because of their inferior mechanical properties and processability. This limits their practical application. To achieve system-level device applications, organic field-effect transistors are one of the key components to be integrated with various sensors. Herein, a successful method for fabricating a biocompatible, ultrathin (≈1.5 µm), lightweight (1.85 g m–2), and mechanically durable all-nanofiber-based organic transistor is reported that can be in conformal contact with curved skin. Furthermore, it is the first development with a substrate-less nanomesh organic field effect transistor. The devices exhibit satisfactory electrical performance, including an on/off value of 3.02 × 104 ± 0.9 × 104, saturation mobility of 0.05 ± 0.02 cm2 V− 1 s− 1, subthreshold slope of 1.7 ± 0.2 V dec–1, and threshold voltage of −6 ± 0.5 V. The mechanism of crack initiation is analyzed, via simulation, to understand the deformation of the nanomesh transistors. Furthermore, active matrix integrated tactile sensors entirely on the nanomeshes is successfully demonstrated, indicating their potential applicability in the field of biomedical electronics. © 2022 Wiley-VCH GmbH.FALS

Washable, stretchable, and reusable core–shell metal nanowire network-based electronics on a breathable polymer nanomesh substrate

Polymer nanofiber-based porous structures, referred to as “breathable devices,” have been recently developed to minimize user discomfort. Although these devices enable conformal integration to the skin with gas permeability, their performance and durability are significantly lower than those of conventional film-based devices. In this study, an ultradurable embedded Ag–Au core–shell nanowire network (AANN) on a nanomesh substrate is fabricated using the intense pulsed light irradiation and electroplating (IPL-EP) process. The AANN is designed to achieve breathability and durability without sacrificing device performance. It can be used in breathable nanomesh electronics and exhibits a low sheet resistance (1.4 Ω sq−1), cycle stability (above 20,000 cycles), stability in chemicals (water-based solutions and highly corrosive H2O2 solution), washability (20 washings), and reusability. Additionally, it is used in reusable conductive electronic textiles, and its applications as a reusable strain sensor for motion detection and wearable heater for thermal therapy are demonstrated. Furthermore, the AANN-based conductive thread exhibits excellent electrical performance (0.3 Ω cm−1) with durability and maintains its electrical characteristics after 50 wash cycles. The proposed process can enable large-scale fabrication of highly durable breathable electronics, electronic textiles, and other biomedical devices. © 2022 The AuthorsTRU

Multi-deformable piezoelectric energy nano-generator with high conversion efficiency for subtle body movements

Wearable devices for remote medical systems require a reliable power supply to enable full operation during long-term processes. Piezoelectric generators are promising energy sources that use human body movements to generate energy. The wearable device should be able to easily deform with tiny skin deformations to achieve continual energy generation from standard body movements. However, conventional piezoelectric devices cannot deform sufficiently in response to small movements, resulting in an extremely low energy-conversion efficiency when mounted on the human skin. In this study, we report on an ultrathin piezoelectric energy nano-generator (U-PENG) based on poly(vinylidene fluoride-trifluoroethylene). Owing to their thin structure (4 µm), the proposed U-PENGs conformally adhere to soft human skin and generate energy from subtle movements, such as eye blinking and breathing. These novel devices provide energy conversion efficiency of ~18.85%, which is ~971% higher than thicker samples with identical structures. Owing to their ultrathin structure, high efficiency, and excellent skin attachability, U-PENGs can be integrated with biodevices for use as power sources. © 2022FALS

Precise Measurement of Grasping Force for Noncollaborative Infants

Among the medical parameters used for infants, the grasping force is particularly important because it indicates their musculoskeletal and neurological development. Although several grasping force measuring devices have been developed for infants, their accuracy and reliability are limited owing to their direction-dependent sensing mechanisms. It is challenging to calculate the direction and area of the ambiguous forces applied by infants, and pediatricians cannot control the grasping method used by them. In this study, a direction-independent grasping force measuring device is proposed that features a high resolution (0.1 kPa), cyclic stability (20 000 cycles), and linear sensitivity (21.73 µV kPa−1), and high accuracy and reliability. The grasping forces (average, minimum, and maximum) of the left (normal state) and right (injection needle inserted: uncomfortable state) hands of a 1-day old infant can be successfully analyzed using the proposed device. It can be used to obtain the standard grasping force data of infants, which can contribute toward understanding the correlation between the grasping force and neurological diseases. The proposed device can be used to quantitatively measure the grasping force of not only infants but also the elderly; therefore, additional studies may report that the grasping force can be a discriminable parameter for identifying neurological diseases. © 2023 Wiley-VCH GmbH.FALS