Simultaneous fabrication of line defects-embedded periodic lattice by topographically assisted holographic lithography

We have demonstrated simultaneous fabrication of designed defects within a periodic structure. For rapid fabrication of periodic structures incorporating nanoscale line-defects at large area, topographically assisted holographic lithography (TAHL) technique, combining the strength of hologram lithography and phase-shift interference, was proposed. Hot-embossing method generated the photoresist patterns with vertical side walls which enabled phase-shift mask effect at the edge of patterns. Embossing temperature and relief height were crucial parameters for the successful TAHL process. Periodic holes with a diameter of 600 nm at a 1 μm-pitch incorporating 250 nm wide line-defects were obtained simultaneously

Omnidirectional stretchable inorganic-material-based electronics with enhanced performance

Inorganic material‐based devices are well known for their high performance, excellent stability, and hence suitability for fast computation and communication. But their nonflexibility and nonstretchability often hinder their application in several emerging areas where conformability with irregular 3D surfaces is required in addition to the high performance. Herein, with honeycomb like patterns, the omnidirectional stretchability and conformability of inorganic material‐based device are demonstrated without sacrificing the performance. The simple method presented here facilitates the transfer of patterned inorganic material‐based devices from rigid poly(methyl methacrylate) (PMMA)/glass substrate onto flexible/stretchable substrate such as polydimethylsiloxane simply by placing a water droplet at the PMMA/glass interface. As a proof of concept, the intrinsically brittle indium–gallium–zinc oxide (IGZO)‐based stretchable photodetector devices are fabricated. These devices can be stretched up to 10% without performance degradation, which is a significant improvement considering the less than ≈1% fracture limit of IGZO. With Au decoration, these devices show 127‐fold higher responsivity (295.3 mA W−1) than planar IGZO devices. The higher fracture strain together with the omnidirectional stretchability underpinned by the honeycomb pattern could allow presented devices to conform to complex hemispherical surfaces such as the human eyes, thus showing significant potential for future high‐performance stretchable electronics

Naked-eye observation of water-forming reaction on palladium etalon: transduction of gas-matter reaction into light-matter interaction

Abstract Palladium is the most prominent material in both scientific and industrial research on gas storage, purification, detection, and catalysis due to its unique properties as a catalyst and hydrogen absorber. Advancing the dynamic optical phenomena of palladium reacting with hydrogen, transduction of the gas-matter reaction into light-matter interaction is attempted to visualize the dynamic surface chemistry and reaction behaviors. The simple geometry of the metal-dielectric-metal structure, Fabry–Perot etalon, is employed for a colorimetric reactor, to display the catalytic reaction of the exposed gas via water-film/bubble formation at the dielectric/palladium interface. The adsorption/desorption behavior and catalytic reaction of hydrogen and oxygen on the palladium surface display highly repeatable and dramatic color changes based on two distinct water formation trends: the foggy effect by water bubbles and the whiteout effect by water film formation. Simulations and experiments demonstrate the robustness of the proposed Fabry–Perot etalon as an excellent platform for monitoring the opto-physical phenomena driven by heterogeneous catalysis.This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. 2021R1A2C2009236 and No. 2020M3H5A108110413). Y.-S.R. acknowledges support from a grant of the Information and Communications Promotion Fund (ICT promotion fund) through the National IT Industry Promotion Agency (NIPA), and Korea University Grant (K2311801). Y.P acknowledges support from KIST Institutional grants (No. 2E32451 and 2V09640

Generated carrier dynamics in V-pit enhanced InGaN/GaN light emitting diode

We investigate the effects of V-pits on the optical properties of a state-of-the art highly efficient, blue InGaN/GaN multi-quantum-well (MQW) light emitting diode (LED) with high internal quantum efficiency (IQE) of > 80%. The LED is structurally enhanced by incorporating pre-MQW InGaN strain relief layer with low InN content and patterned sapphire substrate. For comparison, a conventional (unenhanced) InGaN/GaN MQW LED (with IQE of 46%) grown under similar conditions was subjected to the same measurements. Scanning transmission electron microscopy (STEM) reveals the absence of V-pits in the unenhanced LED, whereas in the enhanced LED, V-pits with {10-11} facets, emerging from threading dislocations (TDs) were prominent. Cathodoluminescence mapping reveals the luminescence properties near the V-pits, showing that the formation of V-pit defects can encourage the growth of defect-neutralizing barriers around TD defect states. The diminished contribution of TDs in the MQWs allows indium-rich localization sites to act as efficient recombination centers. Photoluminescence and time-resolved spectroscopy measurements suggest that the V-pits play a significant role in the generated carrier rate and droop mechanism, showing that the quantum confined Stark effect is suppressed at low generated carrier density, after which the carrier dynamics and droop are governed by the carrier overflow effect

Enhanced NO2 Sensing Performance of Graphene with Thermally Induced Defects

This paper demonstrates the enhanced NO2 sensing performance of graphene with defects generated by rapid thermal annealing (RTA). A high temperature of RTA (300–700 °C) was applied to graphene under an argon atmosphere to form defects on sp2 carbon lattices. The density of defects proportionally increased with increasing the RTA temperature. Raman scattering results confirmed significant changes in sp2 bonding. After 700 °C RTA, ID/IG, I2D/IG, and FWHM (full width at half maximum)(G) values, which are used to indirectly investigate carbon-carbon bonds’ chemical and physical properties, were markedly changed compared to the pristine graphene. Further evidence of the thermally-induced defects on graphene was found via electrical resistance measurements. The electrical resistance of the RTA-treated graphene linearly increased with increasing RTA temperature. Meanwhile, the NO2 response of graphene sensors increased from 0 to 500 °C and reached maximum (R = ~24%) at 500 °C. Then, the response rather decreased at 700 °C (R = ~14%). The results imply that rich defects formed at above a critical temperature (~500 °C) may damage electrical paths of sp2 chains and thus deteriorate NO2 response. Compared to the existing functionalization process, the RTA treatment is very facile and allows precise control of the NO2 sensing characteristics, contributing to manufacturing commercial low-cost, high-performance, integrated sensors

Template-Free Preparation of a Mesopore-Rich Hierarchically Porous Carbon Monolith from a Thermally Rearrangeable Polyurea Network

A mesopore-rich, hierarchically porous carbon monolith was prepared by carbonizing a polyisocyanurate network derived by thermal rearrangement of a polyurea network. The initial polyurea network was synthesized by the cross-linking polymerization of tetrakis(4-aminophenyl)methane (TAPM) and hexamethylene diisocyanate (HDI) in the sol-forming condition, followed by precipitation into nanoparticulate solids in a nonsolvent. The powder was molded into a shape and then heated at 200–400 °C to obtain the porous carbon precursor composed of the rearranged network. The thermolysis of urea bonds to amine and isocyanate groups, the subsequent cyclization of isocyanates to isocyanurates, and the vaporization of volatiles caused sintering of the nanoparticles into a monolithic network with micro-, meso-, and macropores. The rearranged network was carbonized to obtain a carbon monolith. It was found that the rearranged network, with a high isocyanurate ratio, led to a porous carbon with a high mesopore ratio. The electrical conductivity of the resulting carbon monoliths exhibited a rapid response to carbon dioxide adsorption, indicating efficient gas transport through the hierarchical pore structure

Perovskite multifunctional logic gates via bipolar photoresponse of single photodetector

AbstractThe explosive demand for a wide range of data processing has sparked interest towards a new logic gate platform as the existing electronic logic gates face limitations in accurate and fast computing. Accordingly, optoelectronic logic gates (OELGs) using photodiodes are of significant interest due to their broad bandwidth and fast data transmission, but complex configuration, power consumption, and low reliability issues are still inherent in these systems. Herein, we present a novel all-in-one OELG based on the bipolar spectral photoresponse characteristics of a self-powered perovskite photodetector (SPPD) having a back-to-back p+-i-n-p-p+ diode structure. Five representative logic gates (“AND”, “OR”, “NAND”, “NOR”, and “NOT”) are demonstrated with only a single SPPD via the photocurrent polarity control. For practical applications, we propose a universal OELG platform of integrated 8 × 8 SPPD pixels, demonstrating the 100% accuracy in five logic gate operations irrelevant to current variation between pixels.11Nsciescopu

Photosensitive Nanodiscs Composed of Human Photoreceptors for Refractive Index Modulation at Selective Wavelengths

A photoreceptor on the retina acts as an optical waveguide to transfer an individual photonic signal to the cell inside, which is determined by the refractive index of internal materials. Under the photoactivation of photoreceptors making conformational and chemical variation in a visual cell, the optical signal modulation is demonstrated using an artificial photoreceptor-based waveguide with a controlling beam refraction. Two types of nanodiscs are made of human photoreceptor proteins, short-wavelength-sensitive opsin and rhodopsin, with spectral sensitivity. The refractive index and nonlinear features of those two photosensitive nanodiscs are investigated as fundamental properties. The photonanodiscs are photoactivated in such a way that allow refractive index tuning over 0.18 according to the biological function of the respective proteins with color-dependent response.N