Dong-Hyun Lee

Enhanced Catalytic Performance by Zirconium Phosphate‐Modified SiO2‐Supported RuCo Catalyst for Fischer–Tropsch Synthesis

Our zirconium phosphate (ZrP)‐promoted Ru/Co/ZrP/SiO2 catalyst reveals a high catalytic activity and stability during Fischer–Tropsch synthesis. Surface modification with ZrP on SiO2 support with an appropriate amount of phosphorous component prevents cobalt particle aggregation and enhances its stability. These positive effects of ZrP are mainly induced by the spatial confinement of cobalt particles in a thermally stable ZrP matrix, and the catalytic performance was greatly improved when the P/(Zr+P) molar ratio was 0.134 on the CoZrP(0.5) catalyst.

Wetland restoration to enhance biodiversity in urban areas: a comparative analysis

Wetlands mitigation for any activity can be applied to avoid or minimize damage and restore, enhance, or create wetlands as well. New tools for mitigating and creating wetlands are available, including the Wetland Impact Assessment. This article explores many current issues in wetland mitigation and mitigation strategies, using case studies for illustration. We include some general guidelines for successful wetland mitigation based primarily on existing literature review in several cities. We use comparison and analyses on biodiversity improvement and various wetland functions, including flood-risk management, linking people to nature through urban regeneration, and connecting with the natural environment. Also, restoration, enhancement, mitigation, and creation analyses are included.

The effect of Si3N4 additions on the oxidation resistance of TiAl alloys

The oxidation kinetics of TiAl alloys with and without 3 and 5 wt.%additions of Si3N4 particles were studied at 1173 and1273 K in 1 atm of air. The Si3N4 dispersions wereunstable in the matrix phase, so that some of them reacted with titaniumduring sintering to form Ti5Si3 and dissolvednitrogen. The oxide scale formed on TiAl–Si3N4alloys consisted of an outer TiO2, an intermediate(Al2O3+TiO2), and an inner(TiO2+Al2O3) mixed layers. The enhancedalumina-forming tendency, the presence of discrete SiO2 particlesbelow the outer TiO2 layer, and the improved scale adhesion bySi3N4 dispersions were attributable mainly to theincreased oxidation resistance compared to the Si3N4-freeTiAl alloys. Marker experiments showed that, for TiAl–Si3N4 alloys, the primary mode of scale growth was the outward diffusion oftitanium ions for the outer scale and the inward transport of oxygen ionsfor the inner scale.

Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates

We demonstrated AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) with periodic air-voids-incorporated nanoscale patterns enabled by nanosphere lithography and epitaxial lateral overgrowth (ELO) on a 4-in. sapphire substrate. The nanoscale ELO improved the crystal quality of overgrown epitaxial layers at a relatively low growth temperature of 1050u2009°C and at small coalescence thickness less than 2u2009μm. The light output power of the DUV LED was enhanced significantly by 67% at an injection current of 20u2009mA. We attribute such a remarkable enhancement to the formation of embedded periodic air voids which cause simultaneous improvements in the crystal quality of epitaxial layers by ELO and light extraction efficiency enabled by breaking the predominant in-plane guided propagation of DUV photons.

Selective Metal Transfer and its Application to Patterned Multicolor Organic Light‐Emitting Diodes

IO N Various metal patterning technologies have been developed for organic devices such as the shadow-mask process, laseror lamp-induced forward transfer (LIFT), direct metal transfer, and cold welding. In general, the shadow-mask process is widely used in industry for organic optoelectronic devices, such as organic light-emitting diodes (OLEDs) or organic photovoltaic devices. However, the shadow-mask process is diffi cult to apply to large-area substrates. In LIFT techniques, energy is applied with an excimer laser or lamp heater through a photomask to transfer metal patterns onto substrates. [ 1–5 ] In direct metal transfer, a metal is coated onto a patterned mold by various thin fi lm processes and the metal on the protruding surfaces is transfered to substrates by direct adhesive forces. [ 6–8 ] In cold welding, a thin metal fi lm is deposited on the top of a fl at substrate and necessary parts of the metals are removed with soft molds. Cold welding was also successfully applied to the micropatterning of metal cathodes for organic optoelectronic devices. [ 9–11 ] Cold welding is a substractive process, while others are additive processes. The shadow-mask and LIFT processes are classifi ed as noncontact transfer processes, while direct metal transfer and cold welding techniques are contact transfer processes because they need contacts between the donor mold (or fi lm) and substrate for metal patterning. In contact transfer processes, metal patterning is strongly governed by the mechanical rigidity of the molds. [ 8 ] Various soft molds, rigid molds, and rigifl ex models are utilized in various applications. Polydimethyl siloxane, epoxy, and Tefl on are widely used for soft molds due to their good conformal contact onto substrates. Rigid molds such as silicon or quartz are adopted due to their advantages of high resolution and long lifetime. Polyurethane acrylate is widely used as a rigifl ex mold due to its high fl exibility as well as rigidity after curing. In these contact-based techniques, the quality of metal transfer is strongly affected by the molds, and

ADAPTIVE RECONFIGURABLE FLIGHT CONTROL SYSTEM USING MULTIPLE MODEL MODE SWITCHING

Abstract An adaptive reconfigurable flight control system using the mode switching of multiple models is studied. The conventional mode switching method may not guarantee the stability and the performance of the system. In this study, modified adaptive mode switching and decision logic are proposed to improve the adaptiveness of the transient dynamics of a system while maintaining the stability of the closed-loop system in the overall flight envelope. Fixed parameter models and adaptive models are used for mode switching, and a re-initialized adaptive model is also considered. Proper fixed system models are determined by considering various flight conditions with possible aircraft fault models. The mode switching control system is designed based on the selected models for reconfiguration. Numerical simulations are performed to validate the effectiveness of the proposed method.

Effect of Organic Salt Doping on Electron Injection in Single-Layer Polymer Light-Emitting Diodes

We report the effect of organic salt doping on the carrier injection in single-layer polymer light-emitting diodes (PLEDs). From the anomalous behavior in the luminance-voltage characteristic of the salt-doped devices with LiF layer, it was found out that the electron injection through LiF layer occurs competitively with the electrochemical n-doping near the cathode. After the completion of n-doping near the cathode, even without LiF layer the salt-doped devices exhibit the performance comparable to that of the conventional devices with LiF layer. At high operating voltages the salt-doped devices showed the higher brightness and better device stability compared with the conventional devices. We also report for the first time that the salt doping does not affect the device stability appreciably.

Polymer Organic Light-Emitting Devices with Cathodes Transferred under Ambient Conditions

We fabricated polymer organic light-emitting devices (OLEDs) with an aluminum cathode transferred under ambient conditions from a separately prepared transfer film in order to achieve complete, vacuum-free fabrication of polymer OLEDs. Transfer of aluminum (Al) and lithium fluoride on aluminum (LiF/Al) onto polymer OLEDs as a cathode revealed problems in device performance due to native aluminum oxide and the stability of the LiF layer under ambient conditions, respectively. In contrast, the device fabricated with the transfer of cesium carbonate (Cs2CO3)-doped poly(vinyl alcohol) (PVA) on aluminum as a cathode showed lower turn-on voltage, and enhanced efficiency and stability. This method may provide an easy way to fabricate low-cost polymer OLEDs using complete, vacuum-free processes.

Effects of Post-SiH4 and Plasma Treatments on Chemical Vapor Deposited Cu Seeds with Chemical Vapor Deposited TiN Barrier in Porous Low Dielectric Constant and Cu Integration

A Cu seed deposited by chemical vapor deposition (CVD) was integrated with a CVD TiN barrier and electroplated Cu in a double level metal interconnect scheme using a dual damascene process. The post-SiH4 treatment of CVD TiN inhibits agglomeration of thin Cu by improving the wettability of Cu seeds as well as reducing the TiN sheet resistance. Post-plasma treatment on CVD Cu seeds decreases impurities in CVD Cu and eliminates interface voids between the CVD Cu seed and electroplated Cu, improving the gap filling properties of electroplated Cu layers. Inherently poor adhesion of the CVD Cu layers between the Cu barrier metal and the electroplated Cu is overcome by CVD TiN post treatments and CVD Cu post-plasma treatment. Bias-thermal-stress (BTS) tests were performed to verify the effect of post-SiH4 treatment. The SiH4 treated CVD TiN barrier and CVD Cu seed show feasibility for 65-nm technology in terms of low via resistance and chain yields.

Inverted Bottom-Emission Polymer Light-Emitting Devices Doped with Organic Salt

We report the fabrication and characterization of inverted bottom-emission polymer light-emitting devices doped with an organic salt. Unlike conventional organic light-emitting devices, the bottom indium tin oxide (ITO) and top aluminum layers act as the cathode and anode for the inverted devices, respectively. Even though the device structure is reversed in the inverted devices, it was found that their performance is comparable to that of conventional devices. The performance enhancement was attributed to the utilization of a zinc oxide (ZnO) layer and the doping of the organic salt.