Graphene-based organic light-emitting diodes (OLEDs) have recently emerged as a key element essential in next-generation displays and lighting, mainly due to their promise for highly flexible light ...sources. However, their efficiency has been, at best, similar to that of conventional, indium tin oxide-based counterparts. We here propose an ideal electrode structure based on a synergetic interplay of high-index TiO2 layers and low-index hole-injection layers sandwiching graphene electrodes, which results in an ideal situation where enhancement by cavity resonance is maximized yet loss to surface plasmon polariton is mitigated. The proposed approach leads to OLEDs exhibiting ultrahigh external quantum efficiency of 40.8 and 62.1% (64.7 and 103% with a half-ball lens) for single- and multi-junction devices, respectively. The OLEDs made on plastics with those electrodes are repeatedly bendable at a radius of 2.3 mm, partly due to the TiO2 layers withstanding flexural strain up to 4% via crack-deflection toughening.
The development of strain‐insensitive stretchable transparent conductors (TCs) is essential for manufacturing stretchable electronics. Despite recent progress, achieving a high optoelectronic ...performance under applied strain of 50% continues to present a significant challenge in this research field. Herein, an ultratall and ultrathin high aspect ratio serpentine metal structure is described that exhibits a remarkable stretching ability (the resistance remains constant under applied strain of 100%) and simultaneously provides an excellent transparent conducting performance (with a sheet resistance of 7.6 Ω −1 and a transmittance of 90.5%). It is demonstrated that the highly stretchable transparent conducting properties can be attributed to the high aspect ratio feature. A high aspect ratio (aspect ratio of 17–367) structure permits facile deformation of the serpentine structure with in‐plane motion, leading to a high stretching ability. In addition, this structural feature avoids the classic tradeoff between optical transmittance and electrical conductance, providing a high electrical conductance without decreasing the optical transmittance. The practical utility of these devices is tested by using these TCs as stretchable interconnectors among LEDs or in wearable VOC gas sensors.
The development of strain‐insensitive stretchable transparent conductors (TCs) is essential for manufacturing stretchable electronics. Herein, an ultratall and ultrathin high aspect ratio serpentine metal structure is described that exhibits remarkable stretching and simultaneously provides excellent transparent conduction. It is demonstrated that the highly stretchable transparent conducting properties can be attributed to the high aspect ratio feature.
Flexible and mechanically robust gas sensors are the key technologies for wearable and implantable electronics. Herein, the authors demonstrate the high‐performance, flexible nitrogen dioxide (NO2) ...chemiresistors using a series of n‐type conjugated polymers (CPs: PNDIT2/IM‐x) and a polymer dopant (poly(ethyleneimine), PEI). Imine double bonds (C = N) are incorporated into the backbones of the CPs with different imine contents (x) to facilitate strong and selective interactions with NO2. The PEI provides doping stability, enhanced electrical conductivity, and flexibility. As a result, the NO2 sensors with PNDIT2/IM‐0.1 and PEI (1:1 by weight ratio) exhibit outstanding sensing performances, such as excellent sensitivity (ΔR/Rb = 240% @ 1 ppm), ultralow detection limit (0.1 ppm), high selectivity (ΔR/Rb < 8% @ 1 ppm of interfering analytes), and high stability, thereby outperforming other state‐of‐the‐art CP‐based chemiresistors. Furthermore, the thin film of PNDIT2/IM‐0.1 and PEI blend is stretchable and mechanically robust, providing excellent flexibility to the NO2 sensors. Our study contributes to the rational design of high‐performance flexible gas sensors.
In this study, a high‐performance flexible NO2 chemiresistor (IM‐x/P‐y) is developed based on n‐type conjugated polymers containing imine bonds in the backbone. Excellent overall sensing performances with ultralow limit of detection (LOD) are demonstrated.
Collagen is a prominent target of nonenzymatic glycation, which is a hallmark of aging and causes functional alteration of the matrix. Here, we uncover glycation‐mediated structural and functional ...changes in the collagen‐enriched meningeal membrane of the human and mouse brain. Using an in vitro culture platform mimicking the meningeal membrane composed of fibrillar collagen, we showed that the accumulation of advanced glycation end products (AGEs) in the collagen membrane is responsible for glycation‐mediated matrix remodeling. These changes influence fibroblast‐matrix interactions, inducing cell‐mediated ECM remodeling. The adherence of meningeal fibroblasts to the glycated collagen membrane was mediated by the discoidin domain‐containing receptor 2 (DDR2), whereas integrin‐mediated adhesion was inhibited. A‐kinase anchoring protein 12 (AKAP12)‐positive meningeal fibroblasts in the meningeal membrane of aged mice exhibited substantially increased expression of DDR2 and depletion of integrin beta‐1 (ITGB1). In the glycated collagen membrane, meningeal fibroblasts increased the expression of matrix metalloproteinase 14 (MMP14) and less tissue inhibitor of metalloproteinase‐1 (TIMP1). In contrast, the cells exhibited decreased expression of type I collagen (COL1A1). These results suggest that glycation modification by meningeal fibroblasts is intimately linked to aging‐related structural and functional alterations in the meningeal membrane.
Using the in vitro model of AGE‐modified fibrous collagen membrane, we found the changes in adherence and matrix remodeling function of meningeal fibroblast cells on the glycated membrane. The matrix adhesion of meningeal fibroblasts to the glycated collagen membrane is mediated by the discoidin domain‐containing receptor 2 (DDR2), whereas integrin‐mediated adhesion is inhibited. Also, the glycation‐mediated modification of collagen disrupts the collagen membrane at the brain barrier.
The outbreak of coronavirus disease 2019 (COVID-19), which began in December 2019, is still ongoing in Korea, with >9,000 confirmed cases as of March 25, 2020. COVID-19 is a severe acute respiratory ...syndrome Coronavirus 2 (SARS-CoV-2) infection, and real-time reverse transcription-PCR is currently the most reliable diagnostic method for COVID-19 around the world. Korean Society for Laboratory Medicine and the Korea Centers for Disease Prevention and Control propose guidelines for diagnosing COVID-19 in clinical laboratories in Korea. These guidelines are based on other related domestic and international guidelines, as well as expert opinions and include the selection of test subjects, selection of specimens, diagnostic methods, interpretation of test results, and biosafety.
A robust Cu conductor on a glass substrate for thin‐film μLEDs using the flash‐induced chemical/physical interlocking between Cu and glass is reported. During millisecond light irradiation, CuO ...nanoparticles (NPs) on the display substrate are transformed into a conductive Cu film by reduction and sintering. At the same time, intensive heating at the boundary of CuO NPs and glass chemically induces the formation of an ultrathin Cu2O interlayer within the Cu/glass interface for strong adhesion. Cu nanointerlocking occurs by transient glass softening and interface fluctuation to increase the contact area. Owing to these flash‐induced interfacial interactions, the flash‐activated Cu electrode exhibits an adhesion energy of 10 J m−2, which is five times higher than that of vacuum‐deposited Cu. An AlGaInP thin‐film vertical μLED (VLED) forms an electrical interconnection with the flash‐induced Cu electrode via an ACF bonding process, resulting in a high optical power density of 41 mW mm−2. The Cu conductor enables reliable VLED operation regardless of harsh thermal stress and moisture infiltration under a high‐temperature storage test, temperature humidity test, and thermal shock test. 50 × 50 VLED arrays transferred onto the flash‐induced robust Cu electrode show high illumination yield and uniform distribution of forward voltage, peak wavelength, and device temperature.
Flash‐induced robust Cu on a glass substrate for inorganic‐based micro‐light‐emitting diodes (μLEDs) is developed by chemical/physical interlocking. The Cu2O layer at Cu/glass interface and Cu nano‐interlocking resolve the inherent lattice mismatch for strong electrode adhesion, resulting in high optical power (41 mW mm–2) of an AlGaInP vertical thin‐film μLED and robust μLED operation under severe environmental stresses.
As transparent, flexible, and wearable organic electronics degrade under normal outdoor environmental conditions (e.g., water vapor, oxygen, and UV light) and extreme environments, including washing ...or rain, a customized encapsulation technology is required to improve device reliability. Herein, a simple process is presented for fabricating multifunctional hazy substrates (MFHSs) with excellent gas diffusion barrier (GDB), flexibility, UV reflectance, light scattering, and waterproof properties. First, a spiky polyethylene terephthalate (PET) surface is produced with 76.0% optical haze through ion‐beam treatment followed by the formation of a hydrophobic layer to achieve a waterproof effect (contact angle: 153.3°). Then, a multifunctional multibarrier film is fabricated based on a nano‐laminated distributed Bragg reflector and functional polymer on the functional PET substrate to serve as a GDB and UV filter. This multibarrier film has excellent mechanical and chemical stabilities, in addition to having a water vapor transmission rate of 10−6 g m−2 day−1 and UV transmittance of <3%. The so‐fabricated MFHS not only increases the device efficiency by 73% but also enables a highly flexible and environmentally stable organic light–emitting diode. The surface treatment and encapsulation technologies developed in this study are expected to increase the lifetime of organic devices and facilitate high outdoor usability.
The ion‐beam‐treated functional polymersubstrate has an optical haze of >70% and is also superhydrophobic. Furthermore, a multifunctional multibarrier that canovercome the disadvantages of polymer substrate is developed. The encapsulation, based on an atomic‐layer‐deposited nanolaminateand functional polymer, achieves a water vapor transmission rate of 10–6 g m–2 day–1 and UV transmittance of 3%, providing a mechanically andenvironmentally robust multibarrier.
Along with positive SARS-CoV-2 RNA in nasopharyngeal swabs, viral RNA was detectable at high concentration for >3 weeks in fecal samples from 12 mildly symptomatic and asymptomatic children with ...COVID-19 in Seoul, South Korea. Saliva also tested positive during the early phase of infection. If proven infectious, feces and saliva could serve as transmission sources.
Particle bonding physics remains an important area of study in cold spray (CS) deposition. It has been argued that for pure metals, large interfacial strains in particles triggered either by ...adiabatic shear instability (ASI) or hydrostatic plasticity promote bonding while the bonding mechanisms of high entropy alloys (HEA) have not been explored. HEAs are an emerging class of materials that have superior work-hardening ability and are usually resistant to softening, a behavior that is different from pure elements and conventional alloys. In this study, equiatomic CrMnCoFeNi HEA feedstock powder is produced and CS experiments are conducted to explore the deformation evolution of these HEA particles and their bonding characteristics. The shear localization strain of the HEA is theoretically estimated and compared to conventional alloys and elements to explain the deposition behavior of the HEA. Results show that the particle impact morphology is strain rate dependent in addition to being material and microstructure dependent. Electron channelling contrast imaging reveals severe plastic deformation at the lower half of the particles due to the dynamic inertia effect. Deformation nano-twins with a thickness of about 200 nm were observed. HEA/HEA pair has a higher critical velocity compared to HEA/Nickel, HEA/Inconel625 and HEA/Stainless steel 304 pairs. This is attributed to the excellent strain hardening and intermediate softening of the HEA alloy used, which potentially postpones shear localization and impedes bonding, requiring a higher deposition velocity. Finally, it is shown that the ASI based criterion for bonding can predict the deposition mechanism of HEAs more inclusively.
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•Equiatomic CrMnCoFeNi HEA was produced and its cold spray bonding characteristics was explored.•HEA/HEA bonding has a higher critical velocity compared to HEA impact on softer, harder and of similar hardness material.•The high critical velocity of the HEA is attributed to its excellent work hardening and intermediate softening of the HEA.•Adiabatic shear instability based criterion of bonding can more inclusively predict deposition mechanism of HEAs.
Although hexagonal boron nitride (BN) nanostructures have recently received significant attention due to their unique physical and chemical properties, their applications have been limited by a lack ...of processability and poor film quality. In this study, a versatile method to transfer‐print high‐quality BN films composed of densely stacked BN nanosheets based on a desolvation‐induced adhesion switching (DIAS) mechanism is developed. It is shown that edge functionalization of BN sheets and rational selection of membrane surface energy combined with systematic control of solvation and desolvation status enable extensive tunability of interfacial interactions at BN–BN, BN–membrane, and BN–substrate boundaries. Therefore, without incorporating any additives in the BN film and applying any surface treatment on target substrates, DIAS achieves a near 100% transfer yield of pure BN films on diverse substrates, including substrates containing significant surface irregularities. The printed BNs demonstrate high optical transparency (>90%) and excellent thermal conductivity (>167 W m−1 K−1) for few‐micrometer‐thick films due to their dense and well‐ordered microstructures. In addition to outstanding heat dissipation capability, substantial optical enhancement effects are confirmed for light‐emitting, photoluminescent, and photovoltaic devices, demonstrating their remarkable promise for next‐generation optoelectronic device platforms.
A facile approach to print a pure boron nitride (BN) film with both high thermal conductivity (≈167 W m−1 K−1) and optical transparency (≈90%) on various substrates is developed based on desolvation‐induced adhesion switching. This approach allows near‐perfect transfer yield (≈100%) while ensuring good interfacial contact, realizing the full potential of the thermal and optical properties of BN for practical devices.
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