Reliability of Flexible LEDs Investigated by Characterizing Mechanical Properties of Constituent Materials

Department of Materials Science and EngineeringWith increasing consumption of wearable devices, research on flexible displays used as light sources in flexible devices has been conducted in recent years. For realization of flexible, all components of light-emitting diodes (LEDs) must have flexibility. For this reason, studies on organic light-emitting diodes (OLEDs) with high flexibility characteristics are predominant. However, organic semiconductors have disadvantage such as poor color purity with broad full-width half maximum (FWHM) and low-charge carrier mobility. On the other hand, organic-inorganic hybrid perovskites have both characteristics of organic semiconductor materials such as high color purity with narrow full-width half maximum, high charge-carrier mobility and inorganic semiconductor materials such as low processing-cost based on solution process, easy band gap deformation. Recently, many researches have been conducted to apply perovskite to flexible devices, which have the above advantages, and many flexible devices using perovskite have been developed. However, the study on the deformation characteristics of the developed perovskite flexible LEDs is mainly focused on whether the optical properties are maintained under the deformed state. If all the components deform within the elastic deformation range, they will return to their original state when the external force is removed. When a specific component is subjected to plastic deformation, interface separation phenomenon occurs, which causes a problem in driving the device. For the above reasons, it is important to improve the mechanical characteristics of a weakest material in order to improve the flexibility characteristics of the device. There is a lack of research on flexibility analysis based on mechanical properties. Although research on flexible devices using perovskite has progressed through the above research. Organic materials react easily with moisture in air and degrade easily, so encapsulation performance of flexible devices must be improved at the same time. Encapsulation performance of flexible devices has been improved through the development of thin film encapsulation (TFE) materials with flexibility characteristic. However, unlike a rigid device using glass as a substrate, a flexible device uses a polymer-based substrate for its deformation characteristics, so that the substrate functions as a moisture infiltration path. Research on substrates for flexible devices with improved encapsulation performance is needed. In this study, flexibility of perovskite LEDs was analyzed based on the mechanical properties of constituent materials of perovskite LEDs, and substrate for flexible devices with encapsulation properties was developed using silicon dioxide thin films. The critical bending radius of the perovskite LED was set to be the point where the light intensity starts to decrease when repetitive bending deformation was applied at a specific bending radius. The elastic limit of constituent materials of perovskite LEDs was evaluated using a hole nanoindentation. In-situ micro tensile test was conducted to measure the exact elastic limit of perovskite, which was the weakest material among the constituent materials. The critical bend radius was analyzed using the measured perovskite elastic limit and the distance from the neutral plane of the LED. The critical bending radius based on mechanical properties was compared with the critical bending radius which decreased the actual efficiency. The substrate for flexible devices with encapsulation performance was developed using silicon dioxide thin films and analyzed for deformation characteristics. Silicon dioxide thin films were fabricated using sol-gel process. The encapsulation performance of the fabricated silicon dioxide thin film was evaluated by commercialized equipment and accelerating exposure test experiment applied to actual devices. The mechanical properties of silicon dioxide were analyzed by in-situ micro tensile test, and repeated bending tests were performed to evaluate critical bending radius applied to a polymer substrate for flexible device.clos

Bacterial community analysis in upflow multilayer anaerobic reactor (UMAR) treating high-solids organic wastes

A novel anaerobic digestion configuration, the upflow multi-layer anaerobic reactor (UMAR), was developed to treat high-solids organic wastes. The UMAR was hypothesized to form multi-layer along depth due to the upflow plug flow; use of a recirculation system and a rotating distributor and baffles aimed to assist treating high-solids influent. The chemical oxygen demand (COD) removal efficiency and methane (CH4) production rate were 89% and 2.10 L CH4/L/day, respectively, at the peak influent COD concentration (110.4 g/L) and organic loading rate (7.5 g COD/L/day). The 454 pyrosequencing results clearly indicated heterogeneous distribution of bacterial communities at different vertical locations (upper, middle, and bottom) of the UMAR. Firmicutes was the dominant (>70%) phylum at the middle and bottom parts, while Deltaproteobacteria and Chloroflexi were only found in the upper part. Potential functions of the bacteria were discussed to speculate on their roles in the anaerobic performance of the UMAR system

Photo-patternable and transparent films using cellulose nanofibers for stretchable origami electronics

Substantial progress in flexible or stretchable electronics over the past decade has extensively impacted various technologies such as wearable devices, displays and automotive electronics for smart cars. An important challenge is the reliability of these deformable devices under thermal stress. Different coefficients of thermal expansion (CTE) between plastic substrates and the device components, which include multiple inorganic layers of metals or ceramics, induce thermal stress in the devices during fabrication processes or long-term operations with repetitions of thermal cyclic loading-unloading, leading to device failure and reliability degradation. Here, we report an unconventional approach to form photo-patternable, transparent cellulose nanofiber (CNF) hybrid films as flexible and stretchable substrates to improve device reliability using simultaneous electrospinning and spraying. The electrospun polymeric backbones and sprayed CNF fillers enable the resulting hybrid structure to be photolithographically patternable as a negative photoresist and thermally and mechanically stable, presenting outstanding optical transparency and low CTE. We also formed stretchable origami substrates using the CNF hybrid that are composed of rigid support fixtures and elastomeric joints, exploiting the photo-patternability. A demonstration of transparent organic light-emitting diodes and touchscreen panels on the hybrid film suggests its potential for use in next-generation electronics.ope

Benign Pleomorphic Adenoma of the Soft Palate Metastasizing to the Sphenoid Sinus

A benign pleomorphic adenoma is the most common tumor of the salivary glands. This tumor has the potential to metastasize to bone, the head and neck region, visceral organs and skin. Although there a few reports about a benign pleomorphic adenoma metastasizing to the maxillary sinus in the paranasal sinuses, there are no reports about a metastatic benign pleomorphic adenoma in the sphenoid sinus. We report here on a case of a benign pleomorphic adenoma of the soft palate that metastasized to the sphenoid sinus, and we briefly review the relevant clinical literature

Sr2_2IrO4_4/Sr3_3Ir2_2O7_7 superlattice for a model 2D quantum Heisenberg antiferromagnet

Spin-orbit entangled pseudospins hold promise for a wide array of exotic magnetism ranging from a Heisenberg antiferromagnet to a Kitaev spin liquid depending on the lattice and bonding geometry, but many of the host materials suffer from lattice distortions and deviate from idealized models in part due to inherent strong pseudospin-lattice coupling. Here, we report on the synthesis of a magnetic superlattice comprising the single ($n$=1) and the double ($n$=2) layer members of the Ruddlesden-Popper series iridates Sr$_{n+1}$Ir$_{n}$O$_{3n+1}$ alternating along the $c$-axis, and provide a comprehensive study of its lattice and magnetic structures using scanning transmission electron microscopy, resonant elastic and inelastic x-ray scattering, third harmonic generation measurements and Raman spectroscopy. The superlattice is free of the structural distortions reported for the parent phases and has a higher point group symmetry, while preserving the magnetic orders and pseudospin dynamics inherited from the parent phases, featuring two magnetic transitions with two symmetry-distinct orders. We infer weaker pseudospin-lattice coupling from the analysis of Raman spectra and attribute it to frustrated magnetic-elastic couplings. Thus, the superlattice expresses a near ideal network of effective spin-one-half moments on a square lattice

Melatonin receptor 1 B polymorphisms associated with the risk of gestational diabetes mellitus

<p>Abstract</p> <p>Backgrounds</p> <p>Two SNPs in <it>melatonin receptor 1B </it>gene, <it>rs10830963 </it>and <it>rs1387153 </it>showed significant associations with fasting plasma glucose levels and the risk of Type 2 Diabetes Mellitus (T2DM) in previous studies. Since T2DM and gestational diabetes mellitus (GDM) share similar characteristics, we suspected that the two genetic polymorphisms in <it>MTNR1B </it>may be associated with GDM, and conducted association studies between the polymorphisms and the disease. Furthermore, we also examined genetic effects of the two polymorphisms with various diabetes-related phenotypes.</p> <p>Methods</p> <p>A total of 1,918 subjects (928 GDM patients and 990 controls) were used for the study. Two <it>MTNR1B </it>polymorphisms were genotyped using TaqMan assay. The allele distributions of SNPs were evaluated by <it>x</it>²models calculating odds ratios (ORs), 95% confidence intervals (CIs), and corresponding <it>P </it>values. Multiple regressions were used for association analyses of GDM-related traits. Finally, conditional analyses were also performed.</p> <p>Results</p> <p>We found significant associations between the two genetic variants and GDM, <it>rs10830963</it>, with a corrected <it>P </it>value of 0.0001, and <it>rs1387153</it>, with the corrected <it>P </it>value of 0.0008. In addition, we also found that the two SNPs were associated with various phenotypes such as homeostasis model assessment of beta-cell function and fasting glucose levels. Further conditional analyses results suggested that <it>rs10830963 </it>might be more likely functional in case/control analysis, although not clear in GDM-related phenotype analyses.</p> <p>Conclusion</p> <p>There have been studies that found associations between genetic variants of other genes and GDM, this is the first study that found significant associations between SNPs of <it>MTNR1B </it>and GDM. The genetic effects of two SNPs identified in this study would be helpful in understanding the insight of GDM and other diabetes-related disorders.</p