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.

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.

Growing Properties of Carbon Nanowalls According to the Hydrogen Gas Ratio.

In this study, the growth characteristics of carbon nanowalls (CNWs), which are applied to many devices because of their high aspect ratio and excellent electrical characteristics thanks to their two-dimensional structure, were confirmed by changing the ratio of methane (CH4) and hydrogen (H2) therein. In many studies, CNWs were grown using various chemical vapor deposition (CVD) or sputtering methods, with a mixture of CH4 and H2 or argon (Ar) gas. To find the suitable rate, 25 sccm CH4, which is used as the source gas, was first injected into the chamber, and the characteristics were confirmed by changing the amount of H2 gas from 0 to 50 sccm. Ultrasonically cleaned Si wafer was used as the substrate, and the CNW was grown for 10 minutes at microwave power (1300 W, 600°C) using microwave-plasma-enhanced CVD (MPECVD).

Analysis of plasma-grown carbon oxide and reduced-carbon-oxide nanowalls.

In this study, several characteristics of carbon oxide nanowalls (CONWs) and reduced-carbon-oxide nanowalls (rCONWs) activated using plasma and thermochemistry were investigated. To become modified CONW and rCONW, catalyst-free carbon nanowalls (CNWs) were grown on a silicon (Si) wafer via microwave-plasma-enhanced chemical vapor deposition (MPECVD) with a mixture of hydrogen (H2) and methane (CH4) gases. The CONW was modified by oxidizing a CNW on a Si wafer with plasma treatment using oxygen (O2) plasma. Afterwards, the CONW was placed in a rapid-thermal-annealing (RTA) chamber, and H2 gas was injected thereto; therefore, the CONW was reduced by H2 gas. The surface properties of the CONW and rCONW were confirmed via scanning electron microscopy (SEM). Raman spectroscopy was used for structural analysis, and the surface energy of each surface was analyzed by operating the contact angle. The chemical characteristics were observed via X-ray photoelectron spectroscopy (XPS). Hall measurements were applied to investigate the electrical characteristics.