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631 results on '"Park, Jeunghee"'

1. Controllable p$-$n junctions in three$-$dimensional Dirac semimetal Cd$_3$As$_2$ nanowires

Author

Bayogan, Janice Ruth, Park, Kidong, Siu, Zhuo Bin, An, Sung Jin, Tang, Chiu-Chun, Zhang, Xiao-Xiao, Song, Man Suk, Park, Jeunghee, Jalil, Mansoor B. A., Nagaosa, Naoto, Hirakawa, Kazuhiko, Schönenberger, Christian, Seo, Jungpil, and Jung, Minkyung

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We demonstrate a controllable p$-$n junction in a three$-$dimensional Dirac semimetal (DSM) Cd$_3$As$_2$ nanowire with two recessed bottom gates. The device exhibits four different conductance regimes with gate voltages, the unipolar (n$-$n and p$-$p) regime and the bipolar (n$-$p and n$-$p) one, where p$-$n junctions are formed. The conductance in the p$-$n junction regime decreases drastically when a magnetic field is applied perpendicular to the nanowire, which is due to the suppression of Klein tunneling. In this regime, the device shows quantum dot behavior. On the other hand, clear conductance plateaus are observed in the n$-$n regime likely owing to the cyclotron motion of carriers at high magnetic fields. Our experiment shows that the ambipolar tunability of DSM nanowires can enable the realization of quantum devices based on quantum dots and electron optics.

Published
2019
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2. Quantum dots formed in three-dimensional Dirac semimetal Cd$_3$As$_2$ nanowires

Author

Jung, Minkyung, Yoshida, Kenji, Park, Kidong, Zhang, Xiao-Xiao, Yesilyurt, Can, Siu, Zhuo Bin, Jalil, Mansoor B. A., Park, Jinwan, Park, Jeunghee, Nagaosa, Naoto, Seo, Jungpil, and Hirakawa, Kazuhiko

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Abstract

We demonstrate quantum dot (QD) formation in three-dimensional Dirac semimetal Cd$_{3}$As$_{2}$ nanowires using two electrostatically tuned p$-$n junctions with a gate and magnetic fields. The linear conductance measured as a function of gate voltage under high magnetic fields is strongly suppressed at the Dirac point close to zero conductance, showing strong conductance oscillations. Remarkably, in this regime, the Cd$_{3}$As$_{2}$ nanowire device exhibits Coulomb diamond features, indicating that a clean single QD forms in the Dirac semimetal nanowire. Our results show that a p$-$type QD can be formed between two n$-$type leads underneath metal contacts in the nanowire by applying gate voltages under strong magnetic fields. Analysis of the quantum confinement in the gapless band structure confirms that p$-$n junctions formed between the p$-$type QD and two neighboring n$-$type leads under high magnetic fields behave as resistive tunnel barriers due to cyclotron motion, resulting in the suppression of Klein tunneling. The p$-$type QD with magnetic field-induced confinement shows a single hole filling. Our results will open up a route to quantum devices such as QDs or quantum point contacts based on Dirac and Weyl semimetals.

Published
2018
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3. Alloying of ReS2 and VS2 Nanosheets Enhances Electrocatalytic Hydrogen Evolution Reaction.

Author

Ihsan, Junaid, Kwak, In Hye, Kim, Ju Yeon, Zewdie, Getasew Mulualem, Choi, Jun Hyeok, Lee, Sang‐Gil, Lee, Kug‐Seung, Kwon, Ik Seon, Park, Jeunghee, and Kang, Hong Seok

Subjects
HYDROGEN evolution reactions, GIBBS' free energy, TRANSITION metals, SULFURIC acid, DENSITY of states
Abstract

Modulating the electronic structure of transition metal dichalcogenides (TMDs) via alloying is challenging despite the additional potential applications. In this study, a solvothermal reaction is used to synthesize composition‐tuned ReS2–VS2 (Re1‐xVxS2) alloy nanosheets featuring an expanded interlayer distance. Increasing x induces a phase transition from the semiconducting 1T″ phase ReS2 to the metallic 3R‐stacking 1T phase VS2. Alloying via homogeneous atomic mixing renders the nanosheets more metallic and with less oxidation than VS2. First‐principles calculations consistently predict the 1T″–1T phase transition of the atomically mixed alloy structures. The calculation also suggests that intercalation drives the 3R stacking of 1T phase VS2. The Re1‐xVxS2 nanosheets at x = 0.3–0.8 exhibit enhanced electrocatalytic activity toward water‐splitting hydrogen evolution reaction (HER) in an acid electrolyte. In situ X‐ray absorption fine structure measurements reveal that the metallicity of the alloys is fully retained during HER. The density of states and Gibbs free energy calculations show that alloying increases the metallicity and thus effectively activates the basal S atoms toward the HER, supporting the observed increased HER performance of the alloy nanosheets. [ABSTRACT FROM AUTHOR]

Published
2024
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8. Stacking polytypes of 1T′ phase Se-rich transition metal diselenide and their electrocatalytic activity in the hydrogen evolution reaction.

Author

Kim, Ju Yeon, Kwak, In Hye, Kwon, Ik Seon, Sial, Qadeer Akbar, Ihsan, Junaid, Zewdie, Getasew Mulualem, Park, Jeunghee, and Kang, Hong Seok

Abstract

Transition metal dichalcogenides exhibit various stacking polytypes and distinct electronic structures. In this study, first-principles calculations show that chalcogen enrichment induces the phase conversion from 2H to 1T′. Models for Se intercalation and substitution (MoSex and WSex with x > 2) were constructed for the 2H and three stacking polytypes of the 1T′ phase (1T′, 2M, and Td). Se intercalates and substitutes more favorably into the 1T′ polytypes than into the 2H phase. Intercalation in the 1T′ polytypes occurs by forming Se dimers, which is distinct from the Se monomer in the 2H phase. The relative stability predicts that as x increases, the 2H phase undergoes phase conversion preferentially into the 2M phase. On the experimental side, we synthesized Se-rich MoSe2 and WSe2 nanosheets using a colloidal reaction, and confirmed the stacking sequence of the 2M phase using atomic-resolution scanning transmission electron microscopy. The Se-rich 2M phase nanosheets exhibited enhanced electrocatalytic performance in the hydrogen evolution reaction (HER). Gibbs free energy calculations support that excess Se enhances the HER. [ABSTRACT FROM AUTHOR]

Published
2023
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22. Composition-Tuned (MoWV)Se2Ternary Alloy Nanosheets as Excellent Hydrogen Evolution Reaction Electrocatalysts

Author

Kwon, Ik Seon, Lee, Seung Jae, Kim, Ju Yeon, Kwak, In Hye, Zewdie, Getasew Mulualem, Yoo, Seung Jo, Kim, Jin-Gyu, Lee, Kug-Seung, Park, Jeunghee, and Kang, Hong Seok

Abstract

Ternary alloying of transition metal dichalcogenides (TMDs) has the potential for altering the electronic structure of materials to suit electrochemical applications. Herein, we synthesized (MoWV)Se2nanosheets at various compositions viaa colloidal reaction. The mole fraction of V atoms (xV) was successfully increased up to 0.8, producing a metallic phase that is highly durable against hydration. Furthermore, we synthesized (MoW)Se2nanosheets over the entire composition range. The atomic mixing of the ternary alloys is more random than that of the constitutional binary alloys, as supported by first-principles calculations. Compared to binary alloying, ternary alloying more effectively enhanced the electrocatalytic activity for acidic hydrogen evolution reaction (HER). The HER performance increased upon increasing xVto 0.44, and thereafter, it declined at higher xVprimarily owing to surface oxidation. The analysis of Gibbs free energy for H adsorption revealed that ternary alloying strongly activates the basal plane for the HER. VSe2contains numerous sites favorable for H adsorption, facilitating the composition-dependent HER. These results provide a pioneering strategy for designing multicomponent TMD catalysts that maximize the advantages of each component.

Published
2023
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27. Investment of field emission and photoemission properties of high-purity single-walled carbon nanotubes synthesized by hydrogen arc discharge

Author

Ha, Byeongchul, Park, Jeunghee, Shin Young Kim, and Cheol Jin Lee

Subjects
Carbon -- Chemical properties, Carbon -- Atomic properties, Field emission cathodes -- Research, Photoemission -- Research, Chemicals, plastics and rubber industries
Abstract

The relationship between the field emission and the density of states (DOS) of single-walled carbon nanotubes (SWCNTs) synthesized by hydrogen arc-discharge method is investigated. The results have shown that the field emission of SWCNTs can be closely related to the DOS of SWCNTs near the Fermi level.

Published
2006

38. Temperature-dependent growth of vertically aligned carbon nanotubes in the range 800-1100 degrees celsius

Author

Yun Tack Lee, Park, Jeunghee, Young Sang Choi, Hyun Ryu, and Hwack Joo Lee

Subjects
Electron microscopy -- Usage, Nanotubes -- Research, Nanotubes -- Structure, Chemistry
Abstract

The effect of temperature on the growth rate and structure of carbon nanotubes is investigated with the help of electron microscopy, transmission electron microscopy and Raman spectroscopy. The carbon nanotubes were grown vertically aligned on iron nanoparticle deposited silicon substrate by thermal chemical vapor deposition of acetylene in the temperature range 800-1100 degree celsius.

Published
2002

39. Energy-dependent quantum-state-resolved relaxation of highly vibrationally excited pyridine (E (sub)vib = 36 990-40 200 cm (super)1-) through collisions with CO (sub)2

Author

Park, Jeunghee, Li, Ziman, Lemoff, Andrew S., Rossi, Craig, Elioff, Michael S., and Mullin, Amy S.

Subjects
Chemistry, Physical and theoretical -- Research, Pyridine -- Physiological aspects, Quantum chemistry -- Research, Carbon dioxide -- Physiological aspects, Excited state chemistry -- Research, Chemicals, plastics and rubber industries
Published
2002

45. Controllable p–n junctions in three-dimensional Dirac semimetal Cd3As2 nanowires

Author

Bayogan, Janice Ruth, primary, Park, Kidong, additional, Siu, Zhuo Bin, additional, An, Sung Jin, additional, Tang, Chiu-Chun, additional, Zhang, Xiao-Xiao, additional, Song, Man Suk, additional, Park, Jeunghee, additional, Jalil, Mansoor B A, additional, Nagaosa, Naoto, additional, Hirakawa, Kazuhiko, additional, Schönenberger, Christian, additional, Seo, Jungpil, additional, and Jung, Minkyung, additional

Published
2020
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48. Substituent effect of N,N-dialkylamides on the intermolecular hydrogen bonding with thioacetamide

Author

Kim, Nak-Kyoon, Lee, Ho-Jin, Choi, Kee-Hyun, Yu, Jeong-A, Yoon, Chang-Ju, Park, Jeunghee, and Choi, Young-Sang

Subjects
Hydrogen bonding -- Research, Chemicals, plastics and rubber industries
Abstract

Research into the alkyl substituent effect on the intermolecular hydrogen-bonding formation between thioacetamide (TA) as a proton donor and tertiary amide as a proton acceptor in a nonpolar solvent is presented. It is suggested that there is more possibility of hydrogen-bonding formation via syn-H of TA for formamides than acetamides.

Published
2000

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