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507 results on '"Choi, Won‐Kook"'

204. Hybrid polymer-quantum dot based single active layer structured multi-functional device: Organic bistable device, LED and Photovoltaic cells.

Author

Son, Dong Ick, Park, Dong Hee, Byoung Wook Kwon, and Choi, Won Kook

Abstract

We demonstrate the hybrid polymer-quantum dot based multi-functional device (Organic bistable devices, Light-emitting diode, and Photovoltaic cell) with a single active-layer structure consisting of CdSe/ZnS semiconductor quantum-dots (QDs) dispersed in a poly N-vinylcarbazole (PVK) and 1,3,5-tirs-(N-phenylbenzimidazol-2-yl) benzene (TPBi) fabricated on indium-tin-oxide (ITO)/glass substrate by using a simple spin coating technique. The multi-functionality of the device as Organic bistable device (OBD), Light Emitting Diode (LED), and Photovoltaic cell can be successfully achieved by adding an electron transport layer (ETL) TPBi to OBD for attaining the functions of LED and Photovoltaic cell in which the lowest unoccupied molecular orbital (LUMO) level of TPBi is positioned at the energy level between the conduction band of CdSe/ZnS and LiF/Al electrode (band-gap engineering). [ABSTRACT FROM PUBLISHER]

Published
2011
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208. Superhydrophilic surface modification of polyvinylidene fluoride by low energy and high flux ion beam irradiation

Author

Choi Won-Kook, Jung Yeon-Sik, and Park Jong-Yong

Subjects
Materials science, Ion beam, business.industry, Analytical chemistry, Polyvinylidene fluoride, High flux, Ion beam irradiation, chemistry.chemical_compound, Low energy, Ion beam deposition, chemistry, Superhydrophilicity, Surface modification, Optoelectronics, General Materials Science, business
Published
2005
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209. Fabrication of nanostructures on InP(100) surface with irradiation of low energy and high flux ion beams

Author

Y Ermakov, Park Jong Yong, Choi Won-Kook, Choi Hyoung Wook, and Jung Yeon Sik

Subjects
Secondary ion mass spectrometry, Ion beam deposition, Materials science, Ion beam, Ion beam mixing, Physics::Plasma Physics, Sputtering, Physics::Optics, General Materials Science, Atomic physics, Focused ion beam, Ion source, Ion
Abstract

InP(100) crystal surface was irradiated by ion beams with low energy and high flux , Self-organization process induced by ion beam was investigated by examining nano structures formed during ion beam sputtering. As an ion source, an electrostatic closed electron Hall drift thruster with a broad beam size was used. While the incident angle , ion flux (J), and ion fluence were changed and InP crystal was rotated, cone-like, ripple, and anistropic nanostrucuture formed on the surface were analyzed by an atomic force microscope. The wavelength of the ripple is about 40 nm smaller than ever reported values and depends on the ion flux as , which is coincident with the B-H model. As the incident angle is varied, the root mean square of the surface roughness slightly increases up to the critical angle but suddenly decreases due to the decrease of sputtering yield. By the rotation of the sample, the formation of nano dots with the size of is clearly observed.

Published
2005
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211. Enhancement of Photoluminescence and Electrical Properties of Ga-Doped ZnO Thin Film Grown on α-Al2O3(0001) Single-Crystal Substrate by rf Magnetron Sputtering through Rapid Thermal Annealing

Author

Jung Cho, Jung Cho, primary, Jongbum Nah, Jongbum Nah, additional, Min-Seok Oh, Min-Seok Oh, additional, Jae-Hoon Song, Jae-Hoon Song, additional, Ki-Hyun Yoon, Ki-Hyun Yoon, additional, Hyung-Jin Jung, Hyung-Jin Jung, additional, and Won-Kook Choi, Won-Kook Choi, additional

Published
2001
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225. Thin Film Growth and Surface Modification by keV Ion Beam

Author

Choi, Sung-Chang, primary, Park, Yong-Wook, additional, Choi, Won-Kook, additional, Kim, Ki-Hwan, additional, Cho, Jun-Sik, additional, Han, Sung, additional, Cho, Jung, additional, Jung, Sun, additional, Han, Young-Gun, additional, Yoo, Byong-Kook, additional, Jung, Hyung-Jin, additional, and Koh, Seok-Keun, additional

Published
1998
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237. Enhanced photovoltaic performance of inverted polymer solar cells utilizing versatile chemically functionalized ZnO@graphene quantum dot monolayer

Author

Moon, Byung Joon, Lee, Kyu Seung, Shim, Jaeho, Park, Soohyung, Kim, Se Ho, Bae, Sukang, Park, Min, Lee, Chang-Lyoul, Choi, Won Kook, Yi, Yeonjin, Hwang, Jun Yeon, and Son, Dong Ick

Abstract

Recently, interfacial engineering approaches as an efficient strategy for improving the power conversion efficiencies (PCEs) of inverted polymer solar cells (iPSCs) has attracted considerable attention. Among various efficient solutions, solution-processed metal-oxide films prepared from metal oxide sol–gel precursors (or nanoparticles) and polymer surface modifiers are typically used as electron selective interfaces in the inverted cell geometry. To present a more effective strategy for surpassing the limitations of traditional methods, such as an unintended increase in series or contact resistance by incompatibility at the organic/inorganic interface, inherently insulating nature of non-conjugated surface modifiers and oxygen adsorption (or photo-induced doping) of metal-oxide layer, we synthesize chemically surface-modified ZnO@graphene core–shell type quantum dots (ZGQDs) with well-characterization of the chemical, optical and electrical properties, and fabricate iPSCs consisting of ITO/PEIE/ZGQD-OAs/photoactive layer/MoO3/Ag. The mono-layered QDs play the multi-functional role as surface modifier, sub-photosensitizer and electron transport layer. Using this effective approach, we achieve the highest conversion efficiency of ~10.3% resulting from improved interfacial properties and efficient charge transfer based on static quenching and charge transfer reaction from ZnO to graphene nanosheets (with drastically reduced τavg(~ 60ps)), which is verified by various analysis tools.

Published
2016
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239. Nano carbon conformal coating strategy for enhanced photoelectrochemical responses and long-term stability of ZnO quantum dots

Author

Kim, Jung Kyu, Bae, Sukang, Kim, Wanjung, Jeong, Myung Jin, Lee, Sang Hyun, Lee, Chang-Lyoul, Choi, Won Kook, Hwang, Jun Yeon, Park, Jong Hyeok, and Son, Dong Ick

Abstract

A conformal coating strategy with nanocarbon to enhance photoelectrochemical responses and the long-term stability of ZnO quantum dots is described. Strong anchoring bonds between a ZnO core and nanocarbon shell ameliorate the poor electrochemical stability of ZnO (such as photocorrosion) in liquid electrolyte. The conjugation of the graphene QD and C60to the ZnO QDs leads to 71% and 99% quenching of the UV photoluminescence (PL) emission, respectively. Also, the decay time of the nanocomposites at UV wavelengths measured much faster than that for the reference of bare ZnO QDs. The moderate energy states and good charge conductance of the nanocarbons result in ultrafast charge transport from the ZnO core to the nanocarbon shell. Thereby, the ZnO core–nanocarbon shell quantum dots shows significantly improved light harvesting performance. The PEC cell test for water oxidation and conventional degradation test using organic dyes exhibited that the photoelectrochemical activities could be significantly improved. At 1.23V (vs. RHE) in pH 6.9 electrolyte, 6 times enhanced photocurrent density was achieved by the conformal coating with C60(0.235mA/cm2for ZnO–C60photoanodes). In particular, the strong Zn–O–C bond structures on the ZnO surface prevented photoinduced holes from being consumed by the photocorrosion reaction of ZnO, thereby improving long-term stability.

Published
2015
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245. Highly conductive and damp heat stable transparent ZnO based thin films for flexible electronics

Author

Jung, Keun, Choi, Won-Kook, Chae, Keun Hwa, Song, Jong-Han, Yoon, Seok-Jin, Lee, Myung-Hyun, and Choi, Ji-Won

Subjects
*TRANSPARENT electronics, *ZINC oxide thin films, *DOPED semiconductors, *ALUMINUM, *HEAT conduction, *ELECTRIC properties of thin films, *THIN films, *OPTICAL properties, *EFFECT of temperature on alloys
Abstract

Abstract: Al doped ZnO (AZO) thin films were deposited at room temperature by continuous composition spread method. Various compositions of AZO thin films deposited at room temperature were explored to find excellent electrical and optical properties. The explored composition, 3.13wt.% Al doped ZnO, was obtained with the lowest resistivity and the highest transmittance. We deposited the optimized AZO composition by on-axis RF sputtering to deposit uniform large area thin film and got a thin film with superior electrical, optical, and damp heat properties although it deposited at room temperature (resistivity: 6.5×10−4 Ωcm, average transmittance in visible region: 92%). [Copyright &y& Elsevier]

Published
2013
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247. Electrical and optical properties of Ga doped zinc oxide thin films deposited at room temperature by continuous composition spread

Author

Jung, Keun, Choi, Won-Kook, Yoon, Seok-Jin, Kim, Hyun Jae, and Choi, Ji-Won

Subjects
*ZINC oxide thin films, *GALLIUM, *ELECTRIC properties of thin films, *THIN films, *OPTICAL properties, *TEMPERATURE effect, *GLASS, *ELECTRIC resistance, *PRESSURE
Abstract

Abstract: Ga doped ZnO (GZO) thin films were deposited on glass substrates at room temperature by continuous composition spread (CCS) method. CCS is thin films growth method of various Ga x Zn1−x O(GZO) thin film compositions on a substrate, and evaluating critical properties as a function position, which is directly related to material composition. Various compositions of Ga doped ZnO deposited at room temperature were explored to find excellent electrical and optical properties. Optimized GZO thin films with a low resistivity of 1.46×10−3 Ωcm and an average transmittance above 90% in the 550nm wavelength region were able to be formed at an Ar pressure of 2.66Pa and a room temperature. Also, optimized composition of the GZO thin film which had the lowest resistivity and high transmittance was found at 0.8wt.% Ga2O3 doped in ZnO. [Copyright &y& Elsevier]

Published
2010
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248. Polyimide surface modification by linear stationary plasma thruster

Author

Choi, Won-Kook and Park, Dong-Hee

Subjects
*ELECTRIC propulsion, *SURFACE analysis, *POLYIMIDES, *MICROFABRICATION, *CATHODES, *ELECTRON transport, *ION bombardment, *DENSITY currents
Abstract

Abstract: Compared to the conventional circular type, the horse-track shaped proto-type linear stationary plasma thruster (LSPT) was designed and fabricated. A cathode with LaB6 emitter was adopted for trapped electron motion along ceramic wall as an electron source generally attached in the conventional cylindrical SPT. Nevertheless it has a little lower ion beam current density of 0.5 mA/cm2 than conventional cylindrical type SPT with 50 mm diameter, it was also proved very effective in surface modification of polymers. Reactive O2 + and N2O+ ion beam generated from LSPT can reduce the wetting angle 70° of polyimide (PI) down to the small angle less than 10°. 2-layer non-adhesive flexible copper clad laminate (FCCL) with Cu(8 µm)/Cu(200 nm)/Ni–Cr–Mo (20 nm)/PI(38 µm) was fabricated by using LSPT in 300 mm roll-to-roll vacuum coater. Peel strength was 0.66 kgf/cm for as-received sample and 0.42 kgf/cm after thermal test for 168 h at 150 °C, which shows a little higher performance than commercial ones. [Copyright &y& Elsevier]

Published
2009
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249. Metal–Organic Framework‐Assisted Metal‐Ion Doping in All‐Inorganic Perovskite for Dual‐Mode Image Sensing Display (Adv. Funct. Mater. 18/2022).

Author

Oh, Jin Woo, Han, Hyowon, Kim, Hong Hee, Lee, Hyeokjung, Kim, Dongjun, Lee, Jiyeon, Kim, Jiwon, Choi, Won Kook, and Park, Cheolmin

Subjects
PEROVSKITE, METHYLAMMONIUM, CRYSTAL defects, METAL-organic frameworks
Abstract

The perovskite crystals with the defects passivated with the metal ions result in environmentally stable and enhanced photoluminescence of the perovskite for dual-mode image sensing display. Metal-Organic Framework-Assisted Metal-Ion Doping in All-Inorganic Perovskite for Dual-Mode Image Sensing Display (Adv. Funct. Dual-mode sensing display, humidity stability, metal-ion doped perovskites, metal-organic framework nanoparticles, thin all-inorganic perovskite films. [Extracted from the article]

Published
2022
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250. Low energy O2 + and N2O+ ion beam modification of polyimide for improving adhesive strength of Cu/PI in roll-to-roll process

Author

Park, Dong-Hee and Choi, Won-Kook

Subjects
*METALLIC films, *ION bombardment, *POLYIMIDES, *COPPER compounds, *NITROUS oxide, *OXYGEN, *PLASMA gases, *SURFACE energy
Abstract

Abstract: To enhance the weak mechanical durability of directly deposited copper layers on polyimide (PI) film due to their poor adhesive strength, a continuous roll-to-roll process involving surface modification using a reactive ion beam irradiation and in-situ deposition process is studied. The polyimide film is modified by an ion source with a linear stationary plasma thruster (LSPT) in the vacuum roll-to-roll process. An O2 ion beam, with beam energy of 214 eV and beam current density of 0.78 mA/cm2, and N2O ion beam, with 220 eV and 0.69 mA/cm2, irradiate PI film in winding speed of 0.5 m/min. The surface energy increases from 38 mN/m for the pristine PI film to 80 mN/m after beam irradiation at an ion fluence of 3.5×1016 ions/s. After beam irradiation, a 10 nm thick tie layer and 200 nm thick copper layer are successively deposited by in-situ DC magnetron web coating. The peel strength of the copper layer on the PI film is enhanced from 0.4 kgf/cm without ion beam treatment to 0.71 kgf/cm after O2 beam treatment and to 0.75 kgf/cm after N2O beam treatment. This enhancement is closely related to the increase in the polar force originating from the formation of hydrophilic Cyl) groups on the modified PI surface. [Copyright &y& Elsevier]

Published
2009
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