Yun-Su Lee

Fabrication of Glass Fiber Reinforced Composite Films for Flexible Organic Light Emitting Diode Devices

We fabricated transparent composite films which have good thermal stability, low CTE (coefficient of thermal expansion) and high mechanical properties for flexible OLED substrate. Glass fiber reinforced composite films were made by UV light induced chemical crosslinking of composite materials consisted of glass fiber and UV curable resin in film state. It was noted that the pattern of the reinforce glass fiber had important effect on the optical and mechanical properties of the resulting composite film. The performance of the composite films in the ITO thin film deposition process and subsequent OLED device fabrication was better than those of the known polymer films such as PET, PC, and PES.

Draft Genome Sequence of an Anaerobic and Extremophilic Bacterium, Caldanaerobacter yonseiensis, Isolated from a Geothermal Hot Stream

ABSTRACT Caldanaerobacter yonseiensis is a strictly anaerobic, thermophilic, spore-forming bacterium, which was isolated from a geothermal hot stream in Indonesia. This bacterium utilizes xylose and produces a variety of proteases. Here, we report the draft genome sequence of C. yonseiensis, which reveals insights into the pentose phosphate pathway and protein degradation metabolism in thermophilic microorganisms.

Fabrication of Transparent Semiconducting Indium Zinc Tin Oxide Thin Films and Its Wet Chemical Etching Characteristics in Hydrochloric Acid

We have fabricated the transparent semiconducting indium zinc tin oxide (IZTO) thin films on polymeric substrates at room temperature by RF-magnetron sputtering method, and investigated their wet chemical etching behavior in HCl solution. The study has revealed that the control of O2 flow rate during deposition attribute to the variation of resistivity for IZTO films, resulting in the conductor–semiconductor conductivity transition. The increasing etchant molarity and temperature of etching solution lead to the increase in etching rate of IZTO films according to the chemical dissolution reaction. As a result, the IZTO active channel is defined successfully, suggesting sufficient possibility for the application to flexible transparent thin film transistors.

Synthesis and Electro-Optical Properties of Carbazole Containing Copolymers with Different Conjugated Structures for Polymer Light-Emitting Devices

New copolymers such as Poly(9-(4-(2-ethyl-hexyloxy)-3,5-dimethylphenyl)carbazole-alt-aminonaphtalene) [ P1 ] and Poly(4-(bis-methylbiphenyl-alt-9H-carbazol-9-yl)benzenamine) [ P2 ] with chromophores separated by non-conjugated methylene spacers, and Poly(4-(dioctylfluorene-alt-9H-carbazole-9yl)benzenamine) [ P3 ] based on alternating fluorene and amine units in the polymer backbone were synthesized by palladium catalyzed polycondensation reaction. Optical properties of these polymers were characterized in terms of UV/visible absorption and photoluminescence (PL) emission in solution and film state. Maximum PL emission (λmax,PL) of synthesized copolymers were observed in the blue region of 426 nm–460 nm in solution state, but the three polymers all showed large red shift in film state with the green emission. The electro-optical properties of these polymers in polymer light-emitting diode (PLED) devices were investigated from the viewpoint of utilizing the new polymers as emitting layer and hole injection/transport layer. The polymer P3 was found to function both as hole injection and hole transport layer with performance better than that of well known PEDOT:PSS hole injection layer material.

Fabrication of Multiple Gas Barrier Layers Utilizing Roll-to-Roll Sputter and Performance

Flexible organic light emitting diodes (OLEDs) have been studied actively for the potential application to OLED display and OLED lighting. One of the key materials for flexible OLED is the flexible and transparent film substrate which can substitute ITO glass in flat panel OLEDs. In this work we deposited silicon and aluminium oxide and nitride single layer thin films on different flexible substrates such as poly(polyethylene terephthalate) (PET) and poly(polyethylene naphthalate (PEN) to investigate the gas barrier properties. After selecting the polymer film substrate and thin inorganic layer material, the inorganic/organic/inorganic multiple gas barrier was formed on film substrate by using roll-to-roll sputter and their property was examined from the viewpoint of multilayer structure and gas barrier properties for application to flexible substrate of OLED devices.

Reduction of Power Consumption of Counter Electrode Structure in AC-PDP

The low capacitance in the panel contributes to a reduction of power consumption in a Plasma Display Panel system. In this paper, the capacitances of the counter and coplanar electrode structures are compared on the basis of the measurement of discharge and displacement current. The sustain gap of the counter structure is wider than that of the coplanar structure under the same discharge volume. Furthermore, the sustain electrode area of the counter structure is smaller than that of the coplanar structure. Accordingly, the capacitance of the counter structure is lower than that of the coplanar structure for the same discharge volume and sustain gap.

Property of Cu(In,Ga)Se2 Absorption Layer Produced using a Proximity Selenization Method

Cu(In,Ga)Se2 thin films were prepared using co-sputtering and proximity selenization. This new method supplies Se by closely attaching opposite a metal precursor. CuInSe2 thin film was produced at 280°C, and consisted of small structures. As the temperature was increased, more Ga was substituted in place of In, while the X-ray peak of the CuInSe2 shifted to the right. A thin film with a Cu:In:Ga:Se ratio of 1:0.7:0.3:2 was obtained at 480°C, which is comparatively lower than the temperature needed when using Se vapor. This grew into crystals with a diameter of 3–5 μm.

Effects of Thin Film Deposition on Fabrication of Switchable Mirror

In this paper we studied switchable mirrors for application to transparent flat panel displays. The typical structure of switchable mirror has configuration of MgNi/Pd/Ta2O5/HxWO3/ITO. In this study photocatalyst layer (TiO2 or Nb2O5) was used between Pd and Ta2O5 layers. These layers were prepared by RF magnetron sputtering method utilizing TiO2 and Nb2O5 targets under various conditions and their electrochromic properties were investigated by using FE-SEM, EDAX and Nano View system. The transmittances of the Nb2O5 and the TiO2 thin films, could be optimized in the switchable mirror as photocatalyst layer, where they were deposited under the power of 80 W and 70 W, respectively, by the RF magnetron sputter. The characteristics of Nb2O5 and TiO2 transmittance are the outstanding at 80 W, 70 W respectively.

Stability of ITO Films with Oxide Buffer Layer Grown onto PES Substrates

In this paper, ITO films with the oxide buffer layers were deposited by magnetron sputtering technique onto the PES. The oxide buffer layer was formed by a radio frequency (RF) magnetron sputtering method, using SiO2 or TiO2 target. The ITO layers were deposited by a low-frequency (LF) magnetron sputtering technique onto PES/Buffer layer. The sheet resistances of ITO films with the oxide buffer layers grown onto PES substrate were investigated as a function of time in the air and the vacuum. In both cases, the increasing rates of the sheet resistance of the PES/Buffer layer/ITO films are lower than those of the PES/ITO films. In addition, the increasing rates of sheet resistances of the films with the TiO2 buffer layer are lower than those of the films with the SiO2 buffer layer.

Sensory quality characteristics with different beef quality grades and surface texture features assessed by dented area and firmness, and the relation to muscle fiber and bundle characteristics

The main objective of this study was to compare the eating quality among the groups categorized by the Korean beef quality grade and texture feature of exposed muscle surface assessed by extent of dented areas and firmness. Additionally, this study also investigated the effects of fiber and bundle characteristics on texture feature to establish the cause of differences in muscle surface texture. Significant differences were observed in the sensory quality characteristics among the quality grades mainly determined by marbling score (P < 0.05). However, the coarse texture group with a dented surface required a higher initial force to penetrate meat (P < 0.001), was more difficult to break meat into fragments (P < 0.001), and had a higher amount of perceptible residue in the mouth (P < 0.01) compared to the fine texture group. These differences in the surface texture features between the fine and coarse groups could be explained by bundle area and fiber number per each bundle.