Polarized ultraviolet emitters with Al wire-grid polarizers fabricated by solvent-assisted nanotransfer process.

Polarized ultraviolet (UV) emitters are essential for various applications, such as photoalignment devices for liquid crystals, high-resolution imaging devices, highly sensitive sensors, and steppers. To increase the high polarization ratio (PR) of a UV emitter, the grating period should be decreased than that of the visible emitter. However, the fabrication of the short period grating directly on UV emitters is still limited. In this study, we demonstrate that 200, 100, and 50 nm period aluminum (Al)-based wire-grid polarizers (WGPs) can be fabricated directly on UV emitters by a solvent-assisted nanotransfer process. The UV emitter with a grating period of 100 nm shows a PR of 84%, and an electroluminescence efficiency that is 22.5% and 48% higher than those of UV emitters with 50 nm and 200 nm period WGPs, respectively, due to the increased photon extraction efficiency (PEE). The higher PEE is attributed to the optical cavity property of the Al metal reflector with low light loss and the surface plasmon effect of the Al grating layer.

Perovskite-Based Artificial Multiple Quantum Wells.

Semiconductor quantum well structures have been critical to the development of modern photonics and solid-state optoelectronics. Quantum level tunable structures have introduced new transformative device applications and afforded a myriad of groundbreaking studies of fundamental quantum phenomena. However, noncolloidal, III-V compound quantum well structures are limited to traditional semiconductor materials fabricated by stringent epitaxial growth processes. This report introduces artificial multiple quantum wells (MQWs) built from CsPbBr3 perovskite materials using commonly available thermal evaporator systems. These perovskite-based MQWs are spatially aligned on a large-area substrate with multiple stacking and systematic control over well/barrier thicknesses, resulting in tunable optical properties and a carrier confinement effect. The fabricated CsPbBr3 artificial MQWs can be designed to display a variety of photoluminescence (PL) characteristics, such as a PL peak shift commensurate with the well/barrier thickness, multiwavelength emissions from asymmetric quantum wells, the quantum tunneling effect, and long-lived hot-carrier states. These new artificial MQWs pave the way toward widely available semiconductor heterostructures for light-conversion applications that are not restricted by periodicity or a narrow set of dimensions.

Enhanced performance of InGaN/GaN MQW LED with strain-relaxing Ga-doped ZnO transparent conducting layer.

We report the enhanced optical and electrical properties of InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs) with strain-relaxing Ga-doped ZnO transparent conducting layers (TCLs). Ga-doped ZnO was epitaxially grown on p-GaN by metal-organic chemical vapor deposition. The optical output power of a LED with a 500-nm- thick-Ga-doped ZnO TCL increased by 30.9% at 100 mA, compared with that of an LED with an indium tin oxide (ITO) TCL. Raman spectroscopy measurement and the simulation of wavefunction overlap of electron and hole in MQWs revealed that the enhanced optical output power was attributed to the increased internal quantum efficiency due to the decreased compressive strain in the active region. The increase of optical output was also attributed to the increased optical transmittance of the Ga-doped ZnO TCL owing to its higher refractive index compared to that of ITO TCL. Furthermore, the forward voltage of LED with a Ga-doped ZnO TCL was lower than that of LED with an ITO TCL because of the increased carrier concentration and mobility in the Ga-doped ZnO TCL.

Enhanced optical output in InGaN/GaN light-emitting diodes by tailored refractive index of nanoporous GaN.

The light to be trapped inside light-emitting diodes (LEDs) greatly affects the luminous efficiency and device lifetime. Abrupt difference in refractive index between the sapphire substrate and GaN-based LEDs causes light trapping by total internal reflection, however, its optical loss has been taken for granted. In this study, we demonstrate that nanoporous GaN can be used as a refractive-index-matching layer to enhance the light transmittance at the sapphire-GaN interface in InGaN/GaN flip-chip light-emitting diodes (FCLEDs). The porosity and the refractive index of the nanoporous GaN layer are controlled by electrochemical etching of n-type GaN layer. The optical output power of FCLEDs with the nanoporous GaN layer grown on flat and patterned sapphire substrates is increased by 355% and 65% at an injection current of 20 mA, respectively, compared with that of an FCLED without the nanoporous GaN layer. The remarkable enhancement of optical output is mostly attributed to the nanoporous GaN layer which drastically increases the light extraction efficiency by decreasing the reflection of light at the sapphire-GaN interface.

High Efficiency Flip Chip-Based UV Emitter with Indium Tin Oxide Nano Grains/Al Reflector and Periodic Microhole Arrays.

We propose a high efficiency flip chip-based ultraviolet (UV) emitter with aluminum (Al) reflector that includes indium tin oxide (ITO) nano grains for current injection between the Al and p-AlGaN layer. Al has attracted attention as a reflector for high efficiency UV emitters because of its high reflectance in the UV region. To improve the efficiency of UV emitter, we generated periodic microhole arrays on the p-AlGaN layer, which serve as a scattering center in the flip chip structure and enhance the light extraction efficiency. The light output power of the fabricated flip chip-based UV emitter with ITO nano grains/Al reflector and microhole arrays on the p-AlGaN layer is significantly improved by 72% and 45% at an injection current of 20 mA, compared to that of UV emitter with only Al reflector and ITO nano grains/Al reflector.

Transparent Conductive Electrodes of ß-Ga2O3/Ag/ß-Ga2O3 Multilayer for Ultraviolet Emitters.

We investigated the optical and electrical properties of a ß-Ga2O3/Ag/ß-Ga2O3 multilayer transparent conductive electrode deposited on an α-Al2O3 (0001) substrate. For the deposition of a continuous Ag layer, we preliminarily performed anultraviolet-ozone pretreatment of the Ga2O3 bottom layer. To obtain a stable ß-phase of Ga2O3, the ß-Ga2O3/Ag/ß-Ga2O3 multilayer was annealed at 700 °C under N2 atmosphere. The transmittance and sheet resistance of the ß-Ga2O3/Ag/ß-Ga2O3 multilayer were critically affected by the surface morphology and thickness of the Ag interlayer. The multilayer with optimized thicknesses (ß-Ga2O3 top layer: 30 nm; Ag interlayer: 12 nm; ß-Ga2O3 bottom layer: 60 nm) exhibited a resistance of 8.48 Ωsq-1, an average optical transmittance of 87.16% in the ultraviolet wavelength range from 300 to 350 nm, and a figure of merit of 29.81 × 10-3 Ω-1.

Self-standing ZnO nanotube/SiO2 core-shell arrays for high photon extraction efficiency in III-nitride emitter.

Self-standing ZnO nanotube (ZNT) arrays were fabricated on the surface of a GaN-based emitter with an indium tin oxide (ITO) transparent layer using a hydrothermal method and temperature cooling down process. For the greater enhancement of photon extraction efficiency, ZNT/SiO2 core-shell nanostructure arrays were fabricated on the emitter with a 430 nm wavelength. The optical output power of ZNT/SiO2 core-shell arrays on the emitter with ITO electrode was remarkably enhanced by 18.5%, 28.1%, and 55.9%, compared to those of ZNTs, ZNRs on an ITO film on an emitter and ITO film on an emitter as a conventional emitter, respectively. The large enhancement in optical output is attributable to the synergistic effect of efficient photon injection from the ITO/GaN layer to ZNTs because of the well-matched refractive indices and wave-guiding, in addition to the superior photon extraction by the SiO2 coating layer on the ZNTs.

High Reliability of Ag Reflectors with AgCu Alloy for High Efficiency GaN-Based Light Emitting Diodes.

We propose an Ag reflector layer with an AgCu alloy layer as a thermally reliable reflector for high power flip-chip and vertical light emitting diodes (LEDs). By annealing the deposited Ag and Cu layers, intermixed grains and grain boundaries from the alloyed AgCu layer were formed on the LEDs, and CuO nano dots precipitated at the grain boundaries. A thick AgCu layer was deposited to cover the AgCu alloy layer. The precipitation of the CuO nano dots at the grain boundaries suppressed Ag agglomeration, leading to enhanced light reflectance after the annealing process. Consequently, the alloyed AgCu/Ag reflector produced by annealing at a high temperature of 500 °C demonstrated a higher reflectance of 78% and a lower contact resistance of 7.0 × 10-5 Ω · cm2.

Wide Bandgap Transparent Conducting Electrode of FTO/Ag/FTO Structure for Ultraviolet Light-Emitting Diodes.

We investigated the effect of the Ag interlayer thickness on the structural, electrical and optical properties of FTO/Ag/FTO structures designed for use in wide bandgap transparent conducting electrodes. The top and bottom FTO layers were deposited on α-Al2O3 (0001) substrates via RF magnetron sputtering at 300 °C and Ag interlayers were deposited using an e-beam evaporator system. We optimized the figure of merit by changing the thickness of the inserted Ag interlayer from 10 nm to 14 nm, achieving a maximum value of 2.46 × 10-3 Ω-1 and a resistivity of 6.4 × 10-4 Ω · cm using an FTO (70 nm)/Ag (14 nm)/FTO (40 nm) structure. Furthermore, the average optical transmittance in the deep UV range (300 to 330 nm) was 82.8%.

Enhanced optical output power of InGaN/GaN light-emitting diodes grown on a silicon (111) substrate with a nanoporous GaN layer.

We report the growth of InGaN/GaN multiple quantum wells blue light-emitting diodes (LEDs) on a silicon (111) substrate with an embedded nanoporous (NP) GaN layer. The NP GaN layer is fabricated by electrochemical etching of n-type GaN on the silicon substrate. The crystalline quality of crack-free GaN grown on the NP GaN layer is remarkably improved and the residual tensile stress is also decreased. The optical output power is increased by 120% at an injection current of 20 mA compared with that of conventional LEDs without a NP GaN layer. The large enhancement of optical output power is attributed to the reduction of threading dislocation, effective scattering of light in the LED, and the suppression of light propagation into the silicon substrate by the NP GaN layer.

Nano-patterned dual-layer ITO electrode of high brightness blue light emitting diodes using maskless wet etching.

We propose a dual-layer transparent Indium Tin Oxide (ITO) top electrode scheme and demonstrate the enhancement of the optical output power of GaN-based light emitting diodes (LEDs). The proposed dual-layer structure is composed of a layer with randomly distributed sphere-like nano-patterns obtained solely by a maskless wet etching process and a pre-annealed bottom layer to maintain current spreading of the electrode. It was observed that the surface morphologies and optoelectronic properties are dependent on etching duration. This electrode significantly improves the optical output power of GaN-based LEDs with an enhancement factor of 2.18 at 100 mA without degradation in electrical property when compared to a reference LED.

Enhancement of light extraction efficiency of GaN-based light-emitting diodes by ZnO nanorods with different sizes.

The improvement of the optical output power of GaN-based light emitting diodes (LEDs) was achieved by employing nano-sized flat-top hexagonal ZnO rods. ZnO nanorods (NRs) with the average diameters of 250, 350, and 580 nm were grown on p-GaN top surfaces by a simple wet-chemical method at relatively low temperature (90 degrees C) to investigate the effect of the diameter of ZnO NRs on the light extraction efficiency. Consequently, the enhancement by the factor of as high as 2.63 in the light output intensity at 20 mA for the LED with 350 nm ZnO NRs was demonstrated without the increase in the operation voltage compared to the reference LED.

Bioactive compounds from the roots of Asiasarum heterotropoides.

A new tetrahydrofuran lignan, (7S,8R,7'S,8'S)-3-methoxy-3',4'-methylenedioxy-7,9'-epoxylignane-4,7',9-triol (1), and 21 known compounds 2-22 were isolated from the roots of Asiasarum heterotropoides by chromatographic separation methods. The structures of all compounds 1-22 were elucidated by spectroscopic analysis including 1D- and 2D-NMR. Fourteen of these compounds (1-3, 7, 10, 12-17, 19, 21, and 22) were isolated from this species in this study for the first time. All of the isolates were evaluated for their anticancer activities using in vitro assays. Among the 22 tested compounds, two (compounds 5 and 7) induced the downregulation of NO production, FOXP3 expression, and HIF-1α transcriptional activity.

Self-array of one-dimensional GaN nanorods using the electric field on dielectrophoresis for the photonic emitters of display pixel.

Recently, high-efficiency III-nitride photonic emitters (PEs) for next-generation displays have been studied. Although micro-light-emitting diodes (µ-LEDs), one of the III-nitride PEs, have attracted considerable attention because of their high efficiency and size flexibility, they have encountered technical limitations such as high defect rate, high processing cost, and low yield. To overcome these drawbacks of µ-LEDs, a lot of research on PEs using one-dimensional (1D) gallium nitride-related nanorods (GNRs) capable of horizontally self-positioning on the electrodes has been carried out. The degree of array of GNRs on the interdigitated electrodes (IDEs) is an important factor in the efficiency of the PEs using GNRs to obtain excellent single-pixel characteristics. Therefore, in this study, we demonstrate that the improved performance of self-arrayed GNRs was realized using the dielectrophoresis technique by changing the thickness of IDEs. In addition, the shape and size of vertically aligned GNRs were controlled by the wet process, and GNR-integrated PEs (GIPEs) were driven by perfectly horizontally self-arrayed GNRs on IDEs. The electroluminescence (EL) intensity of the GIPEs was measured at 4-20 V and showed a maximum intensity value at 15 V. Over the injection voltage at 20 V, the EL intensity decreased due to the high current density of GIPEs. The external quantum efficiency (EQE) property of the GIPEs showed a similar efficiency droop as that of conventional III-nitride PEs.

Topographic location of acute pontine infarction is associated with the development of progressive motor deficits.

BACKGROUND AND PURPOSE: Motor weakness progression is relatively common in acute pontine infarction and frequently associated with increased functional disability. We designed this study to identify the predictors of progression of motor weakness in patients with pontine infarction during the acute phase. METHODS: We identified consecutive patients with acute ischemic stroke in the pons. Patients were defined as having progressive motor deficits (PMD) if their motor National Institutes of Health Stroke Scale scores increased by ≥1 unit between the maximal and initial neurological deficits. To define the predictors of PMD in patients with a pontine infarct, clinical, laboratory, diffusion-weighted imaging lesion location, and magnetic resonance angiographic variables were investigated. RESULTS: A total of 190 patients (male:female=112:78, 66.4±10.6) were identified, and 49 (25.8%) patients were diagnosed with progressive motor deficits. Logistic multiple regression analysis identified lesion involvement of the lower pons (odds ratio, 3.768; 95% confidence interval, 1.696-8.371) as an independent risk factor contributing to motor progression. Although 34 patients (17.9%) had significant basilar artery stenosis, there was no relationship between PMD in pontine infarct patients and the presence of basilar artery stenosis. Additionally, female and previous hypertension were associated with PMD (odds ratio, 2.651, 95% confidence interval, 1.211-5.802; odds ratio, 3.051, 95% confidence interval, 1.087-9.673). CONCLUSIONS: Our results suggest that lower pons lesions may contribute to progressive motor deficits in patients with isolated acute pontine infarction. Infarct topography is therefore a potential prognostic factor of PMD, because the location of the infarct can affect the extent of ischemic degeneration of the corticospinal tract.

Anti-proliferative neolignans from Saururus chinensis against human cancer cell lines.

Activity-guided fractionation of an 80% EtOH extract from the aerial parts of Saururus chinensis led to isolation of three anti-proliferative neolignans (1-3) along with four flavonoids (4-7) and four aristolactams (8-11). Their chemical structures were identified by analysis of spectroscopic data. All compounds 1-11 were evaluated for their activities against 28 human cancer cell lines using an in vitro cell proliferation assay. Compounds 1-3 showed potent anti-proliferative activities against cervical (C33a, IC50=0.01 µM for 1; 0.28 µM for 2; 2.80 µM for 3) and lung (NCI-H460, IC50=0.05 µM for 1; 1.37 µM for 2; 6.46 µM for 3) cancer cells without any remarkable cytotoxic effects on human normal lung cells as a control. Taken together, these data demonstrated the identification of anti-proliferative neolignans which are active components of S. chinensis.

High efficiency GaN-based light emitting diode with nano-patterned ZnO surface fabricated by wet process.

The improvement of the optical output power of GaN-based light emitting diodes (LEDs) was achieved by a novel bi-layer transparent top electrode scheme. The proposed bi-layer structure is composed of a Ga-doped ZnO layer with nano-patterns obtained solely by wet etching process and an Indium Tin Oxide p-type transparent conducting electrode layer. We employed various wet-etching conditions to maximize light extraction efficiency and it was observed that the crystal morphologies of nano-patterns and optoelectronic properties are dependent on etching duration. Because of ITO under GZO layer, the current spreading was not affected even after formation of nano-patterned surface on the GZO layer by wet etching. Consequently, an enhancement of as high as 43.1% in optical output power at an injection current of 100 mA for the LED with nano-patterns wet-etched by 0.025% HCl for 30 seconds was realized without significant degradation in electrical property when compared to a reference LED.

Ethanol extract of Gleditsia sinensis thorn suppresses angiogenesis in vitro and in vivo.

BACKGROUND: Gleditsia sinensis thorns have been widely used in traditional Korean medicine for the treatment of several diseases, including obesity, thrombosis, and tumor-related diseases. The aim of the study is to determine the antiangiogenic effect of Gleditsia sinensis thorns in vitro and in vivo in a bid to evaluate its potential as an anticancer drug. METHODS: Ethanol extract of Gleditsia sinensis thorns (EEGS) were prepared and used for in vitro and in vivo assays. In vitro antiangiogenic effect of EEGS was determined in HUVEC primary cells by cell migration and tube formation assays. In vivo antiangiogenic effect of EEGS was determined by measuring vessel formation and vascular endothelial cells migrating into the implanted matrigels in nude mice. The angiogenesis-related proteins of which expression levels were altered by EEGS were identified by proteomic analysis. RESULTS: EEGS exerted a dose-dependent antiproliferative effect on HUVEC cells without significant cytotoxicity. Angiogenic properties, such as cell migration and tube formation, were significantly inhibited by EEGS in a dose-dependent manner. New vessel formation was also suppressed by EEGS, as determined by the directed in vivo angiogenesis assays in nude mice. EEGS reduced the expression of proangiogenic proteins, endothelin 1 and matrix metallopeptidase 2, in HUVEC cells. CONCLUSIONS: Our findings suggest that EEGS can inhibit angiogenesis by down-regulating proangiogenic proteins, and therefore it should be considered as a potential anticancer drug targeting tumor-derived angiogenesis.

The determinants of stroke phenotypes were different from the predictors (CHADS2 and CHA2DS2-VASc) of stroke in patients with atrial fibrillation: a comprehensive approach.

BACKGROUND: Atrial fibrillation (AF) is a leading cause of fatal ischemic stroke. It was recently reported that international normalized ratio (INR) levels were associated with infarct volumes. However, factors other than INR levels that affect stroke phenotypes are largely unknown. Therefore, we evaluated the determinants of stroke phenotypes (pattern and volume) among patients with AF who were not adequately anticoagulated. METHODS: We analyzed data pertaining to consecutive AF patients admitted over a 6-year period with acute MCA territory infarcts. We divided the patients according to DWI (diffusion-weighted imaging) lesion volumes and patterns, and the relationship between stroke predictors (the CHADS2 and CHA2DS2-VASc score), systemic, and local factors and each stroke phenotype were then evaluated. RESULTS: The stroke phenotypes varied among 231 patients (admission INR median 1.06, interquartile range (IQR) 1.00-1.14). Specifically, (1) the DWI lesion volumes ranged from 0.04-338.62 ml (median 11.86 ml; IQR, 3.07-44.20 ml) and (2) 46 patients had a territorial infarct pattern, 118 had a lobar/deep pattern and 67 had a small scattered pattern. Multivariate testing revealed that the CHADS2 and CHA2DS2-VASc score were not related to either stroke phenotype. Additionally, the prior use of antiplatelet agents was not related to the stroke phenotypes. Congestive heart failure and diastolic dysfunction were not associated with stroke phenotypes. CONCLUSIONS: The results of this study indicated that the determinants of stroke phenotypes were different from the predictors (i.e., CHADS2 and CHA2DS2-VASc score) of stroke in patients with AF.

Improved Performance of GaN-Based Light-Emitting Diodes Grown on Si (111) Substrates with NH3 Growth Interruption.

We demonstrate the highly efficient, GaN-based, multiple-quantum-well light-emitting diodes (LEDs) grown on Si (111) substrates embedded with the AlN buffer layer using NH3 growth interruption. Analysis of the materials by the X-ray diffraction omega scan and transmission electron microscopy revealed a remarkable improvement in the crystalline quality of the GaN layer with the AlN buffer layer using NH3 growth interruption. This improvement originated from the decreased dislocation densities and coalescence-related defects of the GaN layer that arose from the increased Al migration time. The photoluminescence peak positions and Raman spectra indicate that the internal tensile strain of the GaN layer is effectively relaxed without generating cracks. The LEDs embedded with an AlN buffer layer using NH3 growth interruption at 300 mA exhibited 40.9% higher light output power than that of the reference LED embedded with the AlN buffer layer without NH3 growth interruption. These high performances are attributed to an increased radiative recombination rate owing to the low defect density and strain relaxation in the GaN epilayer.