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Novel Method for Combining Flexible Organic Light-Emitting Diodes with Organic Thin-Film Transistors
Taehyoung Zyung,Hye Yong Chu,Jeong-Ik Lee,Ji Young Oh,Jung Hun Lee,Sang Chul Lim,Seong Hyun Kim 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.I
We present a new method of driving an organic light-emitting diode (OLED) with an organic thin-film transistor (OTFT). The OTFT and the OLED were fabricated on separate plastic substrates and both devices were laminated with silver paste. After driving a 2 × 2 mm2 OLED with an OTFT device, we obtained 180 cd/m2 at a current density of 5 mA/cm2 from the green OLED by using an OTFT with mobility, on-off ratio, threshold voltage, and subthreshold slope of 0.21 cm2/V·s, 103, 32 V, and 20 V/decade, respectively.
AlxGa₁-xAs / AlAs / GaAs계로 이루어진 비대칭 이중 양자우물 구조에서의 광 Luminescence 특성 연구
정태형(Taehyoung Zyung),강태종(Tai-Jong Kang),이종태(Seon-Kyu Han),한선규(Jong-Tai Lee),유병수(Byueng-Su Yoo),이해권(Hae-Kwon Lee),이정희(Jung-Hee Lee),이민영(Min-Yung Lee),김동호(Dong-Ho Kim),임영안(Young-Ahn Leem),우종천(Jong-Chun 한국광학회 1992 한국광학회지 Vol.3 No.3
AlxGa_(1-x)As/AlAs/GaAs계로 이루어진 비대칭 이중 양자우물 구조의 광학적 특성을 photoluminescence, photoluminescence excitation, time-resolved photoluminescence를 통하여 조사하였다. 양자장벽 AlAs의 두께에 따른 특성 변화를 조사하기 위하여 두께를 15Å, 150Å로 제작하였다. 양자장벽이 15Å인 경우 매우 빠른 전자의 관통 현상을 보여 주었으며, 이로 인해 AlxGa_(1-x)As의 여기자 재결합에 해당하는 피크가 관찰되지 않았다. AlAs 양자장벽이 150Å인 경우에는 AlxGa_(1-x)As 양자우물에서 여기자 재결합에 의한 피크가 50 ㎰ 이하로 빠른 decay 시간을 보여 주었으며 이것은 양자장벽과의 Γ-X전이에 의한 것으로 사료되었다. GaAs 양자우물에서의 luminescence decay는 두 시료 모두 1 ㎱정도 이었으나, 15Å인 경우에는 약 100 ㎰의 rise 시간이 존재하였으며 이것은 정공의 관통에 의한 시간으로 판명되었다. Luminescence properties of asymmetric double quantum well structure composed of AlxGa_(1-x)As/AlAs/GaAs have been studied by steady state and time-resolved photoluminescence and phtoluminescence excitation spectroscopy at low temperature. Two quantum well samples with different barrier thickness (15Å and 15Å) were prepared to investigate the dependence of tunneling characteristics on barrier thickness. The abscence of excitonic recombination peak from AlxGa_(1-x)As wen for the 15Å barrier sample indicates a very fast electron tunneling to GaAs well. Meanwhile, Γ-X transition between wen and barrier is supposed to be a major route for the fast decay of luminescence from AlxGa_(1-x)As wen in the 150Å barrier sample. Time-resolved photoluminescence from GaAs wen of 15Å sample shows the exsitence of the rise with 100 ps which is attributed to the hole tunneling.
Semiconducting ZnO Nanofibers as Gas Sensors and Gas Response Improvement by SnO2 Coating
Jaehyun Moon,박종아,이수재,Taehyoung Zyung 한국전자통신연구원 2009 ETRI Journal Vol.31 No.6
ZnO nanofibers were electro-spun from a solution containing poly 4-vinyl phenol and Zn acetate dihydrate. The calcination process of the ZnO/PVP composite nanofibers brought forth a random network of polycrystalline würtzite ZnO nanofibers of 30 nm to 70 nm in diameter. The electrical properties of the ZnO nanofibers were governed by the grain boundaries. To investigate possible applications of the ZnO nanofibers, their CO and NO2 gas sensing responses are demonstrated. In particular, the SnO2-deposited ZnO nanofibers exhibit a remarkable gas sensing response to NO2 gas as low as 400 ppb. Oxide nanofibers emerge as a new proposition for oxide-based gas sensors.
Photobleaching for the Formation of Nonlinear Optical Polymer Waveguide Devices
Kim, Jang Joo,Zyung, Taehyoung,Hwang, Wol Yon,Oh, Min Cheol 한국화학공학회 1996 NICE Vol.14 No.3
A simple but realistic kinetic model has been developed to delineate the refractive index profiles formed by photochemical reaction in nonlinear optical polymers. The effects of the absorption due to the unconverted reactant and the photoproduct are included in the model. The parameters required in the model are obtained from simple transmission experiments. The experimental results are consistent with the model. The refractive index profile is steeper when nonlinear optical polymeric materials are bleached by light with higher absorption. The rate of the bleach depth change becomes slower cs the bleaching proceeds. Small absorption of bleaching light due to the photoproduct has significant effect on the resulting refractive index profiles. The photobleaching process is showen to be accelerated by the addition of a photosensitizer. Photobleaching time has been effectively reduced by a factor of 3--5. Linear and nonlinea.r optical properties of the polymer were little affected try the addition of the photosensitizer. It has also been demonstrated that the photobleaching technique can be utilized to tune the initial state of a directional coupler switch after completing the fabrication of the device. It was shown that successive cross states are passed from the initial cross state by selective bleaching of the gap region. The evolution of the refractive index profiles is successfully applied to predict the evolution of output state.
PHOTOBLEACHING FOR THE FORMATION OF NONLINEAR OPTICAL POLYMER WAVEGUIDE DEVICES
Kim, Jang Joo,Zyung, Taehyoung,Hwang, Wol Yon,Oh, Min Cheol 한국화학공학회 1996 Korean Journal of Chemical Engineering Vol.13 No.2
A simple but realistic kinetic model has been developed to delineate the refractive index profiles formed by photochemical reaction in nonlinear optical polymers. The effects of the absorption due to the unconverted reactant and the photoproduct are included in the model. The parameters required in the model are obtained from simple transmission experiments. The experimental results are consistent with the model. The refractive index profile is steeper when nonlinear optical polymeric materials are bleached by light with higher absorption. The rate of the bleach depth change becomes slower as the bleaching proceeds. Small absorption of bleaching light due to the photoproduct has significant effect on the resulting refractive index profiles. The photobleaching process is shown to be accelerated by the addition of a photosensitizer. Photobleaching time has been effectively reduced by a factor of 3-5. Linear and nonlinear optical properties of the polymer were little affected by the addition of the photosensitizer. It has also been demonstrated that the photobleaching technique can be utilized to tune the initial state of a directional coupler switch after completing the fabrication of the device. It was shown that successive cross states are passed from the initial cross state by selective bleaching of the gap region. The evolution of the refractive index profiles is successfully applied to predict the evolution of output state.
Fabrication and characterization of ZnO nanofibers by electrospinning
박종아,Jaehyun Moon,이수재,Sang-Chul Lim,Taehyoung Zyung 한국물리학회 2009 Current Applied Physics Vol.9 No.3
ZnO nanofibers were fabricated by an electrospinning method using a solution containing sol–gel precursors, polymer and solvent. The as-spun and annealed ZnO/poly(4-vinyl phenol) composite fibers were characterized both structurally and electrically. The composite fibers were completely decomposed to obtain polycrystalline ZnO nanofibers. The crystallinity of ZnO nanofibers improved with increase in annealing temperature. The diameters of ZnO nanofibers after annealing above 600 ℃ ranged from 35 nm to 100 nm. The activation energy of ZnO nanofibers for electrical conduction was inversely proportional to the annealing temperature. The ZnO nanofibers showed CO gas sensing capacity at concentration as low as 1.9 ppm.
Solution-Processible Blue-Light-Emitting Polymers Based on Alkoxy-Substituted Poly(spirobifluorene)
이정익,심홍구,이효영,Hye Yong Chu,Lee-Mi Do,Taehyoung Zyung,Jaemin Lee,Jiyoung Oh 한국전자통신연구원 2005 ETRI Journal Vol.27 No.2
Alkoxy-substituted poly(spirobifluorene)s and their copolymers with a triphenylamine derivative have been synthesized by Ni(0)-mediated polymerization. The polymers were well soluble in common organic solvents. Pure blue-light emissions without the long wavelength emission of poly(fluorene)s have been observed in the fluorescence spectra of polymer thin films. The light emitting diodes with a device configuration of ITO/PEDT:PSS(30 nm)/polymer(60 nm)/LiF(1 nm)/Al(100 nm) have been fabricated. The electroluminescence spectra showed the blue emissions without the long wavelength emission as observed in the fluorescence spectra. The relatively poor electroluminescence quantum yield of the homopolymer (0.017% @ 20 mA/cm2) with color coordinates of (0.16, 0.07) has been improved by the introduction of triphenylamine moiety, and the copolymer with triphenylamine derivative exhibited an electroluminescence quantum yield of 0.15% at 20 mA/cm2 with color coordinates of (0.16, 0.08). Moreover, the introduction of polar side chains to the spirobifluorene moiety enhanced the device performance and led to the quantum yields of 0.6 to 0.7 % at 20 mA/cm2, although there was some expense of color purities.
Wireless Energy Transfer System with Multiple Coils via Coupled Magnetic Resonances
Sanghoon Cheon,Yong-Hae Kim,Seung-Youl Kang,Myung-Lae Lee,Taehyoung Zyung 한국전자통신연구원 2012 ETRI Journal Vol.34 No.4
A general equivalent circuit model is developed for a wireless energy transfer system composed of multiple coils via coupled magnetic resonances. To verify the developed model, four types of wireless energy transfer systems are fabricated, measured, and compared with simulation results. To model a system composed of n-coils, node equations are built in the form of an n-by-n matrix, and the equivalent circuit model is established using an electric design automation tool. Using the model, we can simulate systems with multiple coils, power sources, and loads. Moreover, coupling constants are extracted as a function of the distance between two coils, and we can predict the characteristics of a system having coils at an arbitrary location. We fabricate four types of systems with relay coils, two operating frequencies, two power sources, and the function of characteristic impedance conversion. We measure the characteristics of all systems and compare them with the simulation results. The flexibility of the developed model enables us to design and optimize a complicated system consisting of many coils.
Jang, Moongyu,Park, Youngsam,Jun, Myungsim,Hyun, Younghoon,Choi, Sung-Jin,Zyung, Taehyoung Springer 2010 NANOSCALE RESEARCH LETTERS Vol.5 No.10
<P>Silicon nanowires are patterned down to 30 nm using complementary metal-oxide-semiconductor (CMOS) compatible process. The electrical conductivities of n-/p-leg nanowires are extracted with the variation of width. Using this structure, Seebeck coefficients are measured. The obtained maximum Seebeck coefficient values are 122 μV/K for p-leg and −94 μV/K for n-leg. The maximum attainable power factor is 0.74 mW/m K<SUP>2</SUP> at room temperature.</P>