27 results on '"Jiung Cho"'
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2. Light-Tunable Polarity and Erasable Physisorption-Induced Memory Effect in Vertically Stacked InSe/SnS2 Self-Powered Photodetector
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Yue Zhao, Jiung Cho, Miri Choi, Cormac Ó Coileáin, Sunil Arora, Kuan-Ming Hung, Ching-Ray Chang, Mohamed Abid, and Han-Chun Wu
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General Engineering ,General Physics and Astronomy ,General Materials Science - Published
- 2022
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3. Bioinspired redox-coupled conversion reaction in FeOOH-acetate hybrid nanoplatelets for Na ion battery
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Bum Chul Park, Jiung Cho, Jiliang Zhang, Mawuse Amedzo-Adore, Dae Beom Lee, Sung-Chul Kim, Jong Seong Bae, Young Rang Uhm, Sang-Ok Kim, Jehyoung Koo, Yong-Mook Kang, and Young Keun Kim
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Renewable Energy, Sustainability and the Environment ,General Materials Science ,General Chemistry - Abstract
FeOOH complexed with acetate exploits the stepwise intercalation/conversion and biotic Fe redox, enabling a highly reversible conversion reaction. FeOOH reduction coupled with acetate oxidation after Na ion intercalation gives a solid framework for stable Na ion storage.
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- 2022
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4. Charge density waves and degenerate modes in exfoliated monolayer 2H-TaS2
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Byong Sun Chun, Yecun Wu, Jiung Cho, Yu-Hsin Su, Han-Chun Wu, Cormac Ó Coileáin, Ching-Ray Chang, Duan Zhang, Ming-Chien Hsu, Yao Guo, and Miri Choi
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Phase transition ,Materials science ,02 engineering and technology ,Biochemistry ,03 medical and health sciences ,Distortion ,Monolayer ,General Materials Science ,Electronic band structure ,030304 developmental biology ,0303 health sciences ,degenerate modes ,Crystallography ,Condensed matter physics ,Transition temperature ,Degenerate energy levels ,transition metal dichalcogenides ,charge density waves ,Charge density ,2h-tas2 ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Research Papers ,QD901-999 ,periodic lattice distortion ,0210 nano-technology ,Charge density wave - Abstract
Using temperature-dependent Raman scattering, it is demonstrated for the first time that charge density waves can exist in exfoliated monolayer 2H-TaS2 with a phase transition temperature much higher than that in the bulk., Charge density waves spontaneously breaking lattice symmetry through periodic lattice distortion, and electron–electron and electron–phonon interactions, can lead to a new type of electronic band structure. Bulk 2H-TaS2 is an archetypal transition metal dichalcogenide supporting charge density waves with a phase transition at 75 K. Here, it is shown that charge density waves can exist in exfoliated monolayer 2H-TaS2 and the transition temperature can reach 140 K, which is much higher than that in the bulk. The degenerate breathing and wiggle modes of 2H-TaS2 originating from the periodic lattice distortion are probed by optical methods. The results open an avenue to investigating charge density wave phases in two-dimensional transition metal dichalcogenides and will be helpful for understanding and designing devices based on charge density waves.
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- 2020
5. Grain Growth Behavior and Electrical Properties of 0.96(K0.46−xNa0.54−x)Nb0.95Sb0.05O3–0.04Bi0.5(Na0.82K0.18)0.5ZrO3 Ceramics
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Yeon-Ju Park, Il-Ryeol Yoo, Seong-Hui Choi, Jiung Cho, and Kyung-Hoon Cho
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abnormal grain growth ,lead-free ,piezoelectric ,2D nucleation ,vacancy ,General Materials Science - Abstract
This study investigated the causes of microstructural changes and the resultant electrical properties according to the sintering temperature of 0.96(K0.46−xNa0.54−x)Nb0.95Sb0.05O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 lead-free ceramics by analyzing the correlation between vacancy concentrations and 2D nucleation. When sintered for 4 h, no grain growth occurred for the x = 0.000 composition over a wide temperature range, demonstrating that the existence of initial vacancies is essential for grain growth. As x increased, that is, as the vacancy concentration increased, the critical driving force (ΔGC) for 2D nucleation decreased, and abnormal grain growth was promoted. The number and size of these abnormal grains increased as the sintering temperature increased, but at sintering temperatures above 1100 °C, they decreased again owing to a large drop in ΔGC. The x = 0.005 specimen sintered at 1085 °C exhibited excellent piezoelectric properties of d33 = 498 pC/N and kp = 0.45 due to the large number of large abnormal grains with an 83% tetragonal phase fraction. The x = 0.000 specimen sintered at 1130 °C with suppressed grain growth exhibited good energy storage properties because of its very high relative density and small grain size of 300 to 400 nm.
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- 2022
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6. Efficient Suppression of Charge Recombination in Self-Powered Photodetectors with Band-Aligned Transferred van der Waals Metal Electrodes
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Gang Wu, Hee-Suk Chung, Tae-Sung Bae, Jiung Cho, Kuo-Chih Lee, Hung Hsiang Cheng, Cormac Ó Coileáin, Kuan-Ming Hung, Ching-Ray Chang, and Han-Chun Wu
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General Materials Science - Abstract
Recombination of photogenerated electron-hole pairs dominates the photocarrier lifetime and then influences the performance of photodetectors and solar cells. In this work, we report the design and fabrication of band-aligned van der Waals-contacted photodetectors with atomically sharp and flat metal-semiconductor interfaces through transferred metal integration. A unity factor α is achieved, which is essentially independent of the wavelength of the light, from ultraviolet to near-infrared, indicating effective suppression of charge recombination by the device. The short-circuit current (0.16 μA) and open-circuit voltage (0.72 V) of the band-aligned van der Waals-contacted devices are at least 1 order of magnitude greater than those of band-aligned deposited devices and 2 orders of magnitude greater than those of non-band-aligned deposited devices. High responsivity, detectivity, and polarization sensitivity ratio of 283 mA/W, 6.89 × 10
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- 2021
7. Realizing Vibrant and High-Contrast Reflective Structural Colors from Lossy Metals Supporting Dielectric Gratings
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Jerome K. Hyun, Jiung Cho, Youngji Kim, and Kyungmin Jung
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Materials science ,Birefringence ,business.industry ,sRGB ,General Engineering ,General Physics and Astronomy ,02 engineering and technology ,Dielectric ,Grating ,Lossy compression ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Wavelength ,Optics ,Gamut ,General Materials Science ,0210 nano-technology ,business ,Structural coloration - Abstract
Despite their distinctive chemical properties, lossy metals are generally avoided in the design of structural colors because the optical losses can degrade the color vibrancy. Herein, we demonstrate a strategy that allows lossy metals supporting near-wavelength dielectric gratings to achieve high color vibrancy by benefiting from the optical loss rather than suffering from it. By exciting the grating rotated 45° relative to the incident field, s-polarized (s-pol) and p-polarized (p-pol) light each excites a spectrally distinct resonance, described by a treatment of coupled waveguide-array modes, that retards the phase over the wavelength. Owing to the birefringence, a cross-polarized reflection spectrum displays two sharp peaks from each component that decreases the monochromaticity. We show that lossy metals can minimize the p-pol contribution, leaving the sharp s-pol response to determine the spectrum and generate high color vibrancy. Through this scheme, we demonstrate that lossy metal substrates including Pt, a catalytically active metal, and W, a CMOS-compatible metal, can achieve larger sRGB gamut coverage ratios of 90% and 69%, respectively, than that of 55% from Ag, while maintaining similar pixel contrast ratios to that of Ag.
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- 2019
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8. Strategy for Fabricating Wafer-Scale Platinum Disulfide
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Huei-Ru Fuh, Lei Zhang, Yanhui Chen, Haifeng Fei, Hongjun Xu, Jiung Cho, Miri Choi, Xiufeng Han, Dengyun Chen, Duan Zhang, Cormac Ó Coileáin, Ching-Ray Chang, Han-Chun Wu, Jiafeng Feng, and Hsin-Pan Huang
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Photocurrent ,Electron mobility ,Materials science ,Vapor pressure ,business.industry ,Transistor ,Wide-bandgap semiconductor ,02 engineering and technology ,Chemical vapor deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,law ,Optoelectronics ,General Materials Science ,Wafer ,Thin film ,0210 nano-technology ,business - Abstract
PtS2 is a newly developed group 10 2D layered material with high carrier mobility, wide band gap tunability, strongly bound excitons, symmetrical metallic and magnetic edge states, and ambient stability, making it attractive in nanoelectronic, optoelectronic, and spintronic fields. To the aim of application, a large-scale synthesis is necessary. For transition-metal dichalcogenide (TMD) compounds, a thermally assisted conversion method has been widely used to fabricate wafer-scale thin films. However, PtS2 cannot be easily synthesized using the method, as the tetragonal PtS phase is more stable. Here, we use a specified quartz part to locally increase the vapor pressure of sulfur in a chemical vapor deposition furnace and successfully extend this method for the synthesis of PtS2 thin films in a scalable and controllable manner. Moreover, the PtS and PtS2 phases can be interchangeably converted through a proposed strategy. Field-effect transistor characterization and photocurrent measurements suggest that ...
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- 2019
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9. Nanoporous Silver Telluride for Active Hydrogen Evolution
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Gunn Kim, Dongyeun Won, Jiung Cho, Hagyeong Kwon, Ching Yu Chiang, Chia Hsien Lin, Hionsuck Baik, Dongyeon Bae, Ching Shun Ku, Suyeon Cho, Heejun Yang, Hee Jung Park, Ah Reum Jeong, and Heeju Kim
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Tafel equation ,Materials science ,Nanoporous ,General Engineering ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Silver telluride ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,General Materials Science ,0210 nano-technology ,Platinum ,Hydrogen production - Abstract
Silver-based nanomaterials have been versatile building blocks of various photoassisted energy applications; however, they have demonstrated poor electrochemical catalytic performance and stability, in particular, in acidic environments. Here we report a stable and high-performance electrochemical catalyst of silver telluride (AgTe) for the hydrogen evolution reaction (HER), which was synthesized with a nanoporous structure by an electrochemical synthesis method. X-ray spectroscopy techniques on the nanometer scale and high-resolution transmission electron microscopy revealed an orthorhombic structure of nanoporous AgTe with precise lattice constants. First-principles calculations show that the AgTe surface possesses highly active catalytic sites for the HER with an optimized Gibbs free energy change of hydrogen adsorption (-0.005 eV). Our nanoporous AgTe demonstrates exceptional stability and performance for the HER, an overpotential of 27 mV, and a Tafel slope of 33 mV/dec. As a stable catalyst for hydrogen production, AgTe is comparable to platinum-based catalysts and provides a breakthrough for high-performance electrochemical catalysts.
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- 2021
10. Phase Transition-Induced Temperature-Dependent Phonon Shifts in Molybdenum Disulfide Monolayers Interfaced with a Vanadium Dioxide Film
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Jiung Cho, Jongwon Yoon, A.-Rang Jang, Ki Hoon Shin, Hyeon Ih Ryu, Woong-Ki Hong, Seung-Bae Son, and Jung Inn Sohn
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Phase transition ,Materials science ,Phonon ,Substrate (electronics) ,Chemical vapor deposition ,chemistry.chemical_compound ,symbols.namesake ,chemistry ,Chemical physics ,Monolayer ,symbols ,General Materials Science ,Raman spectroscopy ,human activities ,Molybdenum disulfide ,Raman scattering - Abstract
We report the optical phonon shifts induced by phase transition effects of vanadium dioxide (VO2) in monolayer molybdenum disulfide (MoS2) when interfacing with a VO2 film showing a metal-insulator transition coupled with structural phase transition (SPT). To this end, the monolayer MoS2 directly synthesized on a SiO2/Si substrate by chemical vapor deposition was first transferred onto a VO2/c-Al2O3 substrate in which the VO2 film was prepared by a sputtering method. We compared the MoS2 interfaced with the VO2 film with the as-synthesized MoS2 by using Raman spectroscopy. The temperature-dependent Raman scattering characteristics exhibited the distinct phonon behaviors of the E2g1 and A1g modes in the monolayer MoS2. Specifically, for the as-synthesized MoS2, there were no Raman shifts for each mode, but the enhancement in the Raman intensities of E2g1 and A1g modes was clearly observed with increasing temperature, which could be interpreted by the significant contribution of the interface optical interference effect. In contrast, the red-shifts of both the E2g1 and A1g modes for the MoS2 transferred onto VO2 were clearly observed across the phase transition of VO2, which could be explained in terms of the in-plane tensile strain effect induced by the SPT and the enhancement of electron-phonon interactions due to an increased electron density at the MoS2/VO2 interface through the electronic phase transition. This study provides further insights into the influence of interfacial hybridization for the heterogeneous integration of 2D transition-metal dichalcogenides and strongly correlated materials.
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- 2021
11. Mitrofanovite, Layered Platinum Telluride, for Active Hydrogen Evolution
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Heejun Yang, Ning Ling, Hagyeong Kwon, Hionsuck Baik, Jiung Cho, Sukmin Jeong, Dongyeun Won, Suyeon Cho, Karam Park, Hee Jung Park, Dongyeon Bae, and Jayoon Yang
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010302 applied physics ,Tafel equation ,Materials science ,Exchange current density ,chemistry.chemical_element ,02 engineering and technology ,Overpotential ,021001 nanoscience & nanotechnology ,01 natural sciences ,Catalysis ,chemistry.chemical_compound ,Chemical engineering ,chemistry ,Telluride ,0103 physical sciences ,Monolayer ,General Materials Science ,0210 nano-technology ,Platinum ,Hydrogen production - Abstract
Two-dimensional (2D) layered catalysts have been considered as a class of ideal catalysts for hydrogen evolution reaction (HER) because of their abundant active sites with almost zero Gibbs energy change for hydrogen adsorption. Despite the promising performance, the design of stable and economic electrochemical catalyst based on 2D materials remains to be resolved for industrial-scale hydrogen production. Here, we report layered platinum tellurides, mitrofanovite Pt3Te4, which serves as an efficient and stable catalyst for HER with an overpotential of 39.6 mV and a Tafel slope of 32.7 mV/dec together with a high current density exceeding 7000 mA/cm2. Pt3Te4 was synthesized as nanocrystals on a metallic molybdenum ditelluride (MoTe2) template by a rapid electrochemical method. X-ray diffraction and high-resolution transmission microscopy revealed that the Pt3Te4 nanocrystals have a unique layered structure with repeated monolayer units of PtTe and PtTe2. Theoretical calculations exhibit that Pt3Te4 with numerous edges shows near-zero Gibbs free-energy change of hydrogen adsorption, which shows the excellent HER performance as well as the extremely large exchange current density for massive hydrogen production.
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- 2020
12. Variation of spin-orbit torque and spin transport properties by V alloying in β-W-based magnetic heterostructures
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Gyu Won Kim, Jeong Kyu Lee, Taehyun Kim, Min Hyeok Lee, In Ho Cha, Jiung Cho, OukJae Lee, and Young Keun Kim
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Mechanics of Materials ,Mechanical Engineering ,Metals and Alloys ,General Materials Science ,Condensed Matter Physics - Published
- 2022
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13. Core-shell heterostructure-enabled stress engineering in vanadium dioxide nanobeams
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Jongwon Yoon, Ki Hoon Shin, Ji Yong Bae, Su Yong Lee, Jiung Cho, Woong-Ki Hong, Jung Inn Sohn, and Docheon Ahn
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Stress (mechanics) ,Phase transition ,Materials science ,Phase (matter) ,Shell (structure) ,Cylinder stress ,General Materials Science ,Heterojunction ,Composite material ,Elastic modulus ,Amorphous solid - Abstract
In strongly correlated materials (SCMs), especially for vanadium dioxide (VO2), manipulating physical properties through stress engineering is an important issue for the use of ultrafast metal-insulator transition (MIT) in device applications. Recent research efforts have mainly focused on modulation and related phenomena of physical properties by epitaxial and mechanical stresses in VO2 films or anisotropic nanocrystals. However, inhomogeneous stress in such planar and nanocrystal systems leads to complications induced by phase competitions or the creation of intermediate phases. Here, we demonstrate the core-shell heterostructures-enabled stress engineering on MIT, which provides accommodation of uniform axial stress and control of phase transition pathways in VO2 nanobeams. Specifically, the VO2 nanobeams with an amorphous Al2O3 shell undergo a simple and direct MIT at lower temperatures without intermediate phases, distinctly different from pristine nanobeams with coexisting phases. For the core-shell nanobeams, the VO2 core sustains a uniform compressive stress state along the nanobeam length caused by shell formation, which can be attributed to the different thermal behaviors coupled to the elastic modulus between the VO2 and shell. Our results can lead to better engineering of phase transitions in SCMs, providing the beneficial effect of suppressing inhomogeneities during the MIT process.
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- 2021
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14. Abnormally High‐Lithium Storage in Pure Crystalline C 60 Nanoparticles (Adv. Mater. 43/2021)
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Chae-Ryong Cho, Minjoon Park, Injun Jeon, Mihee Park, Dong-Hwa Seo, Se-Young Jeong, Linghong Yin, Jiung Cho, Il Jeon, Su Jae Kim, and Dae Hyung Lee
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Materials science ,chemistry ,Chemical engineering ,Mechanics of Materials ,Mechanical Engineering ,Nanoparticle ,chemistry.chemical_element ,General Materials Science ,Lithium ,Phase evolution - Published
- 2021
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15. Abnormally High‐Lithium Storage in Pure Crystalline C 60 Nanoparticles
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Su Jae Kim, Minjoon Park, Mihee Park, Jiung Cho, Injun Jeon, Chae-Ryong Cho, Il Jeon, Linghong Yin, Se-Young Jeong, Dong-Hwa Seo, and Dae Hyung Lee
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Materials science ,Fullerene ,Mechanical Engineering ,Diethyl carbonate ,chemistry.chemical_element ,Tetragonal crystal system ,chemistry.chemical_compound ,Crystallinity ,chemistry ,Chemical engineering ,Mechanics of Materials ,General Materials Science ,Lithium ,Orthorhombic crystal system ,Graphite ,Ethylene carbonate - Abstract
Li+ intercalates into a pure face-centered-cubic (fcc) C60 structure instead of being adsorbed on a single C60 molecule. This hinders the excess storage of Li ions in Li-ion batteries, thereby limiting their applications. However, the associated electrochemical processes and mechanisms have not been investigated owing to the low electrochemical reactivity and poor crystallinity of the C60 powder. Herein, a facile method for synthesizing pure fcc C60 nanoparticles with uniform morphology and superior electrochemical performance in both half- and full-cells is demonstrated using a 1 m LiPF6 solution in ethylene carbonate/diethyl carbonate (1:1 vol%) with 10% fluoroethylene carbonate. The specific capacity of the C60 nanoparticles during the second discharge reaches ≈750 mAh g-1 at 0.1 A g-1 , approximately twice that of graphite. Moreover, by applying in situ X-ray diffraction, high-resolution transmission electron microscopy, and first-principles calculations, an abnormally high Li storage in a crystalline C60 structure is proposed based on the vacant sites among the C60 molecules, Li clusters at different sites, and structural changes during the discharge/charge process. The fcc of C60 transforms tetragonal via orthorhombic Lix C60 and back to the cubic phase during discharge. The presented results will facilitate the development of novel fullerene-based anode materials for Li-ion batteries.
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- 2021
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16. Simultaneous large continuous band gap tunability and photoluminescence enhancement in GaSe nanosheets via elastic strain engineering
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Mohamed Abid, Yecun Wu, Miri Choi, Duan Zhang, Igor V. Shvets, Huei-Ru Fuh, Jiung Cho, Byong Sun Chun, Mourad Abid, Cormac Ó Coileáin, Ching-Ray Chang, Jing Jing Wang, Huajun Liu, Xuju Jiang, Hongjun Xu, and Han-Chun Wu
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Work (thermodynamics) ,Photoluminescence ,Materials science ,Strain (chemistry) ,Renewable Energy, Sustainability and the Environment ,business.industry ,Band gap ,Exciton ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Strain engineering ,0103 physical sciences ,Optoelectronics ,General Materials Science ,Charge carrier ,Electrical and Electronic Engineering ,010306 general physics ,0210 nano-technology ,business ,Electronic band structure - Abstract
For applications in wearable human-device interfaces and optoelectronics, flexible materials capable of supporting spatial and uninterrupted bandgap tunability are of immense value. We demonstrate theoretically and experimentally the wide bandgap tunability of GaSe nanosheets, with simultaneous PL enhancement, via elastic strain engineering at room temperature. The elastic strain gives rise to a continuously variable electronic band structure profile, with a rate of 40 meV/1%, and a 3-fold enhancement in PL intensity is achieved when a uniaxial strain of 1% is introduced. An additional effect is that a new exciton state arises when the strain is raised beyond 0.6%. This work suggests that strain engineering can effectively modulate/control the generation, separation, transport, and recombination of photo-induced charge carriers in GaSe, making it a valuable material for flexible optoelectronic-mechanical applications.
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- 2017
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17. Ferroelectric Transition in Sr- and W-Doped BaTiO3 Solid Solutions
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Jayoon Yang, Heeju Ahn, Yujin Cho, Hee Jung Park, Dongyeon Bae, Jiung Cho, Eunjeong Lee, and Suyeon Cho
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Technology ,BaTiO3 ,Materials science ,QH301-705.5 ,QC1-999 ,02 engineering and technology ,Crystal structure ,Dielectric ,01 natural sciences ,Tetragonal crystal system ,Lattice constant ,substitution ,0103 physical sciences ,General Materials Science ,Biology (General) ,QD1-999 ,Instrumentation ,010302 applied physics ,Fluid Flow and Transfer Processes ,Condensed matter physics ,Physics ,Process Chemistry and Technology ,Doping ,General Engineering ,Curie temperature ,Engineering (General). Civil engineering (General) ,021001 nanoscience & nanotechnology ,Ferroelectricity ,ferroelectricity ,Computer Science Applications ,Chemistry ,TA1-2040 ,0210 nano-technology ,Solid solution - Abstract
We synthesized Sr- and W-doped BaTiO3 (BTO) polycrystals by using a solid-state reaction method. The X-ray diffraction results showed that Sr and W atoms occupied the Ba and Ti sites in tetragonal BTO, respectively, and there were changes in the lattice constants and the volumes in the Sr- and W-doped BTO. We found a change in the latent heat and the Curie temperature (TC) during the transition between the ferroelectric and paraelectric phases while increasing the contents of Sr and W in the Sr- and W-doped BTO. This can be explained by the fact that the doping of Sr and W atoms in BTO prevented a distinct transition between the ferroelectric tetragonal and paraelectric cubic structures by decreasing the c/a ratio to a value close to unity. This study shows a way toward a strategy for modulating a crystal structure by using proper dopants for future applications in ferroelectricity-based devices.
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- 2021
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18. Highly Sensitive, Selective, Stable, and Flexible NO 2 Sensor Based on GaSe
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Conor P. Cullen, Cormac Ó Coileáin, Ching-Ray Chang, Jiung Cho, Óscar Leonardo Camargo Moreira, Tanja Stimpel-Lindner, Yanfeng Zhao, Miri Choi, Byong Sun Chun, Han-Chun Wu, Huei-Ru Fuh, Georg S. Duesberg, and Duan Zhang
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Materials science ,Mechanics of Materials ,General Materials Science ,Nanotechnology ,Industrial and Manufacturing Engineering ,Highly sensitive - Published
- 2020
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19. Time-Resolved Photoluminescence Properties of ZnO Thin Films Evaporated by Atomic Layer Deposition
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Jiung Cho, Weon-Sik Chae, and Myung-Jin Lee
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Materials science ,Photoluminescence ,business.industry ,Exciton ,Reflectance spectroscopy ,Biomedical Engineering ,Bioengineering ,General Chemistry ,Condensed Matter Physics ,Bohr model ,symbols.namesake ,Atomic layer deposition ,Modulation ,symbols ,Atomic layer epitaxy ,Optoelectronics ,General Materials Science ,Thin film ,business - Abstract
We have studied time-resolved photoluminescence (PL) properties of ZnO thin films which were grown by layer-by-layer manner using atomic layer deposition (ALD) method. The deposited film thickness was estimated by X-ray reflectance spectroscopy, which proved that the ALD system deposited -1.57 Å/cycle in thickness. As-grown films showed typical band-edge and surface defect induced emissions. The evaluated PL lifetimes showed interesting trend as the film thickness approaching to exciton Bohr diameter. Moreover, PL lifetime imaging technique clearly showed the characteristic lifetime modulation with changing film thickness in both band-edge and surface defect emissions.
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- 2015
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20. Creating and Optimizing Interfaces for Electric-Field and Photon-Induced Charge Transfer
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Jiung Cho, Byoungnam Park, Kevin Whitham, and Elsa Reichmanis
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Materials science ,Light ,Exciton ,General Physics and Astronomy ,Electron ,Dielectric ,Electron Transport ,Pentacene ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,Electromagnetic Fields ,Electric field ,Materials Testing ,General Materials Science ,Physics::Chemical Physics ,Photons ,business.industry ,General Engineering ,Heterojunction ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Threshold voltage ,chemistry ,Nanoparticles ,Optoelectronics ,Field-effect transistor ,business - Abstract
We create and optimize a structurally well-defined electron donor-acceptor planar heterojunction interface in which electric-field and/or photon-induced charge transfer occurs. Electric-field-induced charge transfer in the dark and exciton dissociation at a pentacene/PCBM interface were probed by in situ thickness-dependent threshold voltage shift measurements in field-effect transistor devices during the formation of the interface. Electric-field-induced charge transfer at the interface in the dark is correlated with development of the pentacene accumulation layer close to PCBM, that is, including interface area, and dielectric relaxation time in PCBM. Further, we demonstrate an in situ test structure that allows probing of both exciton diffusion length and charge transport properties, crucial for optimizing optoelectronic devices. Competition between the optical absorption length and the exciton diffusion length in pentacene governs exciton dissociation at the interface. Charge transfer mechanisms in the dark and under illumination are detailed.
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- 2012
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21. High power rechargeable batteries
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Jiung Cho, Huigang Zhang, William P. King, Paul V. Braun, and James H. Pikul
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High peak ,Materials science ,Energy transfer ,Energy density ,Figure of merit ,General Materials Science ,Nanotechnology ,High power density ,Engineering physics ,Lithium-ion battery ,Energy storage ,Power density - Abstract
Energy and power density are the key figures of merit for most electrochemical energy storage systems. Considerable efforts worldwide have been made to improve the energy density of rechargeable (secondary) batteries, as this is critical for most applications. As the penetration of batteries into ever more demanding applications has increased, power density, the allowed rate of energy transfer per unit volume or mass, is becoming equally important. High power density batteries have the potential to be rapidly charged, possibly in a few minutes or less, and can also deliver high peak discharge powers. Normally increases in power density are only possible through significant reductions in energy density, however emerging materials research is showing this needs not to be the case. Here we discuss emerging concepts in high power batteries, with a particular focus on Li-ion based chemistries.
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- 2012
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22. TEM Analysis of Multilayered Co/Cu Nanowire Synthesized by DC Electrodeposition
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Young Keun Kim, Soon Mee Choi, Jiung Cho, and Cheol Jin Kim
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Materials science ,Anodizing ,Magnetism ,Tripod (photography) ,Nanowire ,Oxide ,Pulsed DC ,Polishing ,Nanotechnology ,Condensed Matter Physics ,Microstructure ,Atomic and Molecular Physics, and Optics ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,General Materials Science - Abstract
As-received multilayered Co/Cu nanowire arrays were examined by TEM, which were synthesized by pulsed DC electrodeposition using anodized aluminum oxide (AAO) templates. The multilayered Co/Cu nanowire exhibited magnetism in the perpendicular direction to the long wire axis. These nanowire can be applied to sensor array, magnetic bead(biocompatible), MRI contrast enhancing agent, ferro-fluid. Although the characterization of the multilayered Co/Cu nanowire using XRD and VSM and microstructural analysis using TEM on the bare nanowires extracted from AAO templates have been reported, interface analysis between Co and Cu phase or HREM analysis has not been reported in detail. We have prepared TEM specimen with large thin area which was appropriate for the interface analysis between Co and Cu layer without removing AAO templates using tripod polishing method. Tripod polishing proved very efficient to secure the large observable area during TEM session since the polishing angle can be precisely controlled, regardless of the mechanical strength differences in constituents. Thus we could observe not only the interface between Co and Cu layer but also the interface between the metallic layers and AAO templates. Microstructure, composition, and the concentration variation of each Co and Cu layer and the interfaces were analyzed with TEM and STEM.
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- 2007
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23. Magnetic nanodiscs fabricated from multilayered nanowires
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Ji Hyun Min, Boo Hyun An, Jiung Cho, Young Keun Kim, and Daniel S. Choi
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Pore size ,Materials science ,Anodizing ,business.industry ,Biomedical Engineering ,Nanowire ,Oxide ,Bioengineering ,Nanotechnology ,General Chemistry ,Condensed Matter Physics ,chemistry.chemical_compound ,chemistry ,Etching (microfabrication) ,Magnet ,Optoelectronics ,General Materials Science ,business ,Layer (electronics) ,Nanodisc - Abstract
We report a simple, high throughput synthesis method of producing magnetic nanodiscs, in which the diameter and thickness are easily controlled. This method consists of two steps: (1) Electrodeposition for growing multilayered nanowires and (2) Selective etching of sacrificial layers. The electrodeposition step results in a bundle of multilayered nanowires. The nanowires consist of alternating layers of magnetic (e.g., Co) and sacrificial materials (e.g., Cu) inside the nanometer-sized pores of an anodized aluminum oxide (AAO) template. The diameter of each layer is determined by pore size, while the thickness is controlled by electrodeposition time. The selective wet etching step removes sacrificial layers, leaving the magnetic nanodiscs. Through this process, the magnetic nanodiscs are fabricated with aspect ratios ranging from 0.25 to 2.0.
- Published
- 2015
24. Capacitance–voltage analysis of electrical properties for WSe2field effect transistors with high-k encapsulation layer
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Jiung Cho, Jun Eon Jin, Ho Kyun Jang, Jong Mok Shin, Miri Choi, Min Youl You, Gyu Tae Kim, and Seung Pil Ko
- Subjects
010302 applied physics ,Materials science ,business.industry ,Mechanical Engineering ,Doping ,Field effect ,Bioengineering ,Fermi energy ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Threshold voltage ,Atomic layer deposition ,Semiconductor ,Mechanics of Materials ,0103 physical sciences ,Optoelectronics ,General Materials Science ,Field-effect transistor ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,High-κ dielectric - Abstract
Doping effects in devices based on two-dimensional (2D) materials have been widely studied. However, detailed analysis and the mechanism of the doping effect caused by encapsulation layers has not been sufficiently explored. In this work, we present experimental studies on the n-doping effect in WSe2 field effect transistors (FETs) with a high-k encapsulation layer (Al2O3) grown by atomic layer deposition. In addition, we demonstrate the mechanism and origin of the doping effect. After encapsulation of the Al2O3 layer, the threshold voltage of the WSe2 FET negatively shifted with the increase of the on-current. The capacitance-voltage measurements of the metal insulator semiconductor (MIS) structure proved the presence of the positive fixed charges within the Al2O3 layer. The flat-band voltage of the MIS structure of Au/Al2O3/SiO2/Si was shifted toward the negative direction on account of the positive fixed charges in the Al2O3 layer. Our results clearly revealed that the fixed charges in the Al2O3 encapsulation layer modulated the Fermi energy level via the field effect. Moreover, these results possibly provide fundamental ideas and guidelines to design 2D materials FETs with high-performance and reliability.
- Published
- 2018
- Full Text
- View/download PDF
25. Hydrothermal fabrication of three-dimensional secondary battery anodes
- Author
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Eric S. Epstein, Paul V. Braun, Jiung Cho, Junjie Wang, Xing-Jiu Huang, Huigang Zhang, William P. King, Jinhuai Liu, Jinyun Liu, and James H. Pikul
- Subjects
Battery (electricity) ,Materials science ,Fabrication ,Mechanics of Materials ,Mechanical Engineering ,Electrode ,Inorganic chemistry ,Nanoparticle ,General Materials Science ,Nanotechnology ,Hydrothermal circulation ,Anode ,Nanomaterials - Abstract
A generalized hydrothermal strategy for fabricating three-dimensional (3D) battery electrodes is presented. The hydrothermal growth deposits electrochemically active nanomaterials uniformly throughout the complex 3D mesostructure of the scaffold. Ni inverse opals coated with SnO2 nanoparticles or Co3O4 nanoplatelets, and SiO2 inverse opals coated with Fe3O4 are fabricated, all of which show attractive properties including good capacity retention and C-rate performances.
- Published
- 2014
26. Inverse Hall–Petch relation of nanostructured Ni films prepared by electrodeposition
- Author
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Young Keun Kim, Jin Woo Cho, Jiung Cho, Young Jin Choi, Moon Kyu Cho, and Jun Hua Wu
- Subjects
Morphology (linguistics) ,Materials science ,Agglomerate ,Magnetism ,Ultimate tensile strength ,Metallurgy ,General Physics and Astronomy ,General Materials Science ,Texture (crystalline) ,Thin film ,Composite material ,Current density ,Grain boundary strengthening - Abstract
We report the morphology, texture, mechanical properties of Ni films with nanosized grains prepared by electrodeposition as a function of current density. With an increase in current density, the morphology of the nanostructured films was greatly affected and the textures changed from face-centered cubic (1 1 1)- to (2 0 0)-orientation. Consequently, the textural and microstructural alteration exerted strong influence on the hardness of the films, leading to decrease in the hardness (in particular, the inverse Hall–Petch relation) as current density increased, attributed to the distribution of colonies of grain agglomerate and the variation of directional tensile strength.
- Published
- 2010
- Full Text
- View/download PDF
27. Quantum Confinement and Gas Sensing of Mechanically Exfoliated GaSe
- Author
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Askar Syrlybekov, Cormac Ó Coileáin, Hongjun Xu, Lisheng Zhang, Han-Chun Wu, Huajun Liu, Miri Choi, Mohamed Abid, Xiao Liu, Duan Zhang, Byong Sun Chun, Yecun Wu, Georg S. Duesberg, Yanqi Liu, Haomao Wang, Mourad Abid, Kangho Lee, and Jiung Cho
- Subjects
Materials science ,business.industry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,7. Clean energy ,01 natural sciences ,Molecular physics ,Industrial and Manufacturing Engineering ,0104 chemical sciences ,symbols.namesake ,Optics ,Stack (abstract data type) ,Mechanics of Materials ,Quantum dot ,Molecular vibration ,Monolayer ,symbols ,General Materials Science ,Density functional theory ,0210 nano-technology ,business ,Raman spectroscopy ,Layer (electronics) ,Temperature coefficient - Abstract
GaSe layers with thicknesses ranging from a monolayer to 100 nm are successfully mechanically exfoliated for use in gas sensing. In combination with density functional theory calculations, general guidelines to determine the number of layers using Raman spectra are presented. With decreasing layer numbers, quantum confinement induces a red-shift for out-of-plane modes and a blue-shift for in-plane modes. The relative Raman shifts of the out-of-plane vibrational modes A′1(11) and A′1(22) grow exponentially with decreasing stack thickness from 100 to 1 layers. Moreover, the change in first-order temperature coefficient (χ) also increases exponentially as the number of layers is reduced, with the value of the first-order temperature coefficient of the A′1(22) mode of monolayer GaSe (≈−1.99 × 10−2 cm−1 K−1) being almost double that of 100 layer GaSe (≈−1.22 × 10−2 cm−1 K−1). Finally, the exfoliated GaSe is used for gas sensing and shows high sensitivity, displaying a minimum detection limit of 4 ppm for NH3 at room temperature, confirming the potential of mechanically exfoliated GaSe in high-sensitivity gas sensors.
- Published
- 2016
- Full Text
- View/download PDF
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