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4. Direct evidence of electronic interaction at the atomic-layer-deposited MoS2 monolayer/SiO2 interface

Author

Lee, Minji, Kim, Yejin, Mohamed, Ahmed Yousef, Lee, Han-Koo, Ihm, Kyuwook, Kim, Dae Hyun, Park, Tae Joo, and Cho, Deok-Yong

Subjects
Condensed Matter - Materials Science
Abstract

The electronic structure of an atomic-layer-deposited MoS2 monolayer on SiO2 was investigated using X-ray absorption spectroscopy (XAS) and synchrotron X-ray photoelectron spectroscopy (XPS). The angle-dependent evolution of the XAS spectra and the photon-energy-dependent evolution of the XPS spectra were analyzed in detail using an ab-initio electronic structure simulation. Although similar to the theoretical spectra of an ideal free-standing MoS2 ML, the experimental spectra exhibit features that are distinct from those of an ideal ML, which can be interpreted as a consequence of S-O van der Waals (vdW) interactions. The strong consensus among the experimental and theoretical spectra suggests that the vdW interactions between MoS2 and adjacent SiO2 layers can influence the electronic structure of the system, manifesting a substantial electronic interaction at the MoS2-SiO2 interface.

Published
2021
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7. Direct Probing of Oxygen Loss from the Surface Lattice of Correlated Oxides during Hydrogen Spillover

Author

Yoon, Hyojin, Kim, Yongjin, Crumlin, Ethan J, Lee, Donghwa, Ihm, Kyuwook, and Son, Junwoo

Subjects
Chemical Sciences, Physical Chemistry, Affordable and Clean Energy, Physical Sciences, Chemical sciences, Physical sciences
Abstract

Hydrogen spillover is a catalytic process that occurs by surface reaction and subsequent diffusion to reversibly provide a massive amount of hydrogen dopants in correlated oxides, but the mechanism at the surface of correlated oxides with metal catalyst are not well understood. Here we show that a significant amount of oxygen is released from the surface of correlated VO2 films during hydrogen spillover, contrary to the well-established observation of the formation of hydrogen interstitials in the bulk part of VO2 films. By using ambient-pressure X-ray photoelectron spectroscopy, we prove that the formation of surface oxygen vacancies is a consequence of a favorable reaction for the generation of weakly adsorbed H2O from surface O atoms that have low coordination and weak binding strength. Our results reveal the importance of in situ characterization to prove the dynamic change during redox reaction and present an opportunity to control intrinsic defects at the surface.

Published
2019

8. Electrodeless method for ultra-low mobility with carrier-resolution of nanochannel.

Author

Kim, Yongjin, Nguyen, Thao Phuong, Yang, Mihyun, Yoon, Hyojin, Sharma, Manoj Kumar, Lee, Jungsub, Lee, Hoyeol, Oh, Suar, Ree, Moonhor, Son, Junwoo, Shim, Ji Hoon, Kim, Jeehoon, Lim, Seong Chu, and Ihm, Kyuwook

Subjects
ELECTRON mobility, ELECTRON spectroscopy, NANOSTRUCTURED materials, ELECTRONIC equipment, CHARGE carriers, CHARGE carrier mobility
Abstract

As the channel lengths of electronic devices are scaled down to the nanometer range, the conventional methods to evaluate charge-carrier mobility approach a technical limit that is imposed by interfering effects of the electrode and forcing field. In this study, we demonstrate that electron spectroscopy provides additional (yet hidden) information on unipolar charge transport, which is free from conventional problems. We demonstrate that the estimated effective diffusion current through the target sample allows the measurement that is precise enough (10−4 cm2/V s) to obtain the mobility of electrons μelectron and holes μhole in nanolength organic channels. Using this method, we show how μelectron and μhole are correlated with the local structural order of poly(3-hexylthiophene) at the nanoscale. This method enables in situ charge-resolved observations of μelectron and μhole by eliminating the need for electrode and forcing field and will help to expand our understanding of charge conduction in nanoscale materials. [ABSTRACT FROM AUTHOR]

Published
2023
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13. Restoration of Topological Surface State by Vacuum Annealing in Magnetically Doped Topological Insulator

Author

Kim, Jinsu, Shin, Eun-Ha, Sharma, Manoj K., Ihm, Kyuwook, Dugerjav, Otgonbayar, Hwang, Chanyong, Lee, Hwangho, Ko, Kyung-Tae, Park, Jae-Hoon, Kim, Miyoung, Kim, Hanchul, and Jung, Myung-Hwa

Subjects
Condensed Matter - Materials Science
Abstract

The introduction of magnetic order on the surface of topological insulators in general breaks the two-dimensional character of topological surface state (TSS). Once the TSS disappears, it is improbable to restore the topological surface properties. In this report, we demonstrate that it is possible to restore the inherent TSS by ultra-high vacuum annealing. Starting from an antiferromagnetic Gd-doped Bi2Te3, that has surface state gap without TSS properties, after annealing we observed the gap closing as well as typical TSS features in physical properties. The microscopic mechanism of atomic migration and TSS restoration by annealing process is unraveled by the combination of scanning tunneling microscopy measurements and density functional theory calculations. This approach to control the surface of topological insulators and stabilize the TSS simply by vacuum annealing provides a new platform towards the exploitation of their topological properties., Comment: 21 pages, 4 figures, Supplementary information

Published
2017

14. Multi‐Purpose Improvements in Catalytic Activity for Li‐Ion Deposited TiO2, SnO2, and CeO2 Nanoparticles through Oxygen‐Vacancy Control.

Author

Hoang, Dung Thanh, Lim, Donghoon, Kang, Myung Jong, Yu, Hyejin, Pham, Vy Ngoc, Park, Joon Ho, Ihm, Kyuwook, Kim, Hyun Sung, Ahn, Hyun S., and Lee, Hangil

Subjects
SURFACE chemistry, CATALYTIC activity, SUSTAINABLE design, PHOTOCATALYSTS, SUSTAINABILITY, ELECTROCATALYSTS, HYDROGEN evolution reactions
Abstract

Controlling the number of oxygen vacancies (Vos) in metal‐oxide nanoparticles (MO NPs; TiO2, SnO2, and CeO2) using Li‐ions has been shown to endow MO NPs with improved photocatalytic and electrocatalytic properties. Increasing the number of Vos in nanostructures provides a foundation for efficient multi‐use catalyst designs that facilitate biomass oxidation reactions and improve electrocatalytic activity. Herein, the trends in the properties of MO‐based catalysts are investigated with varying amounts of Vos achieved by Li‐ion deposition. The controlled introduction of Vos into MO NPs tunes the band structures and surface chemistry, leading to enhanced activities of the NPs as photocatalysts for the selective oxidation of 2,5‐hydroxymethylfurfural and as electrocatalysts for acidic hydrogen evolution. It is believed that Li‐ion deposition in the MO matrix provides a novel approach for optimizing oxide‐based catalyst defect engineering, thereby enabling more efficient biomass conversion and water splitting. These findings contribute significantly to the field of multi‐purpose catalysis and are expected to inspire new catalyst designs for a more sustainable future. The results provide a pathway for the facile and efficient engineering of surface defect structures on catalytic metal oxide NPs toward designing high‐performance photocatalysts. [ABSTRACT FROM AUTHOR]

Published
2024
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16. Influence of LaFeO3 Surface Termination on Water Reactivity

Author

Stoerzinger, Kelsey A, Comes, Ryan, Spurgeon, Steven R, Thevuthasan, Suntharampillai, Ihm, Kyuwook, Crumlin, Ethan J, and Chambers, Scott A

Subjects
Chemical Sciences, Physical Chemistry, Physical Sciences, Chemical sciences, Physical sciences
Abstract

The polarity of oxide surfaces can dramatically impact their surface reactivity, in particular, with polar molecules such as water. The surface species that result from this interaction change the oxide electronic structure and chemical reactivity in applications such as photoelectrochemistry but are challenging to probe experimentally. Here, we report a detailed study of the surface chemistry and electronic structure of the perovskite LaFeO3 in humid conditions using ambient-pressure X-ray photoelectron spectroscopy. Comparing the two possible terminations of the polar (001)-oriented surface, we find that the LaO-terminated surface is more reactive toward water, forming hydroxyl species and adsorbing molecular water at lower relative humidity than its FeO2-terminated counterpart. However, the FeO2-terminated surface forms more hydroxyl species during water adsorption at higher humidity, suggesting that adsorbate-adsorbate interactions may impact reactivity. Our results demonstrate how the termination of a complex oxide can dramatically impact its reactivity, providing insight that can aid in the design of catalyst materials.

Published
2017

17. Migration of Mg in Na–O–Mg Configuration for Oxygen Redox of Sodium Cathode

Author

Yu, Jun Ho, primary, Voronina, Natalia, additional, Yaqoob, Najma, additional, Kim, Sungkyu, additional, Paidi, Anil Kumar, additional, Ahn, Docheon, additional, Ihm, Kyuwook, additional, Chae, Keun Hwa, additional, Jeong, Min-Gi, additional, Jung, Hun-Gi, additional, Guillon, Olivier, additional, Kaghazchi, Payam, additional, and Myung, Seung-Taek, additional

Published
2023
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18. Ultralow-dielectric-constant amorphous boron nitride

Author

Hong, Seokmo, Lee, Chang-Seok, Lee, Min-Hyun, Lee, Yeongdong, Ma, Kyung Yeol, Kim, Gwangwoo, Yoon, Seong In, Ihm, Kyuwook, Kim, Ki-Jeong, Shin, Tae Joo, Kim, Sang Won, Jeon, Eun-chae, Jeon, Hansol, Kim, Ju-Young, Lee, Hyung-Ik, Lee, Zonghoon, Antidormi, Aleandro, Roche, Stephan, Chhowalla, Manish, Shin, Hyeon-Jin, and Shin, Hyeon Suk

Published
2020
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19. Rotation Curve of Galaxies by the Force Induced by Mass of Moving Particles

Author

Ihm, Kyuwook and Lee, Kyoung-Jea

Subjects
Physics - General Physics
Abstract

We suggest that there is a novel force which is generated by the mass of relatively moving particles. The new force which we named Mirinae Force is a counterpart of the magnetic force operating between electrically charged moving particles. Instead of using the conventional dark matter, we applied the mirinae force to a particular model system of the spiral galaxy in which most of the galaxy's mass is located within the central region where some portion of the inner mass is in revolving motion at a relativistic speed. The calculation yielded three important results that illustrate the existence of mirinae force and validate the proposed model: First, the mirinae force in this model explains why most of the matters in the galactic disk are in the circular motion which is similar to cycloid. Second, the mirinae force well explains not only the flat rotation curve but also the varied slope of the rotation curve observed in the spiral galaxies. Third, at the flat velocity of 220 Km/s, the inner mass of the Milky Way calculated by using the proposed model is 6.0\times10^11 M\odot, which is very close to 5.5\times10^11 M\odot (r <50 Kpc, including Leo I) estimated by using the latest kinematic information. This means that the mirinae force well takes the place of the dark matter of the Milky Way.

Published
2012
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20. High Open-circuit Voltage of Graphene-Based Photovoltaic Cells Modulated by Layer-by-Layer Transfer

Author

Ihm, Kyuwook, Lee, Kyung-jae, Lim, Jong Tae, Kwon, Jae Wook, Kang, Tai-Hee, Chung, Sukmin, Bae, Sukang, Kim, Jin Ho, Hong, Byung Hee, and Yeom, Geun Young

Subjects
Condensed Matter - Materials Science
Abstract

Graphene has shown great application opportunities in future nanoelectronic devices due to its outstanding electronic properties. Moreover, its impressive optical properties have been attracting the interest of researchers, and, recently, the photovoltaic effects of a heterojunction structure embedded with few layer graphene (FLG) have been demonstrated. Here, we report the photovoltaic response of graphene-semiconductor junctions and the controlled open-circuit voltage (Voc) with varying numbers of graphene layers. After unavoidably adsorbed contaminants were removed from the FLGs, by means of in situ annealing, prepared by layer-by-layer transfer of the chemically grown graphene layer, the work functions of FLGs showed a sequential increase as the graphene layers increase, despite of random interlayer-stacking, resulting in the modulation of photovoltaic behaviors of FLGs/Si interfaces. The surface photovoltaic effects observed here show an electronic realignment in the depth direction in the FLG heterojunction systems, indicating future potential toward solar devices utilizing the excellent transparency and flexibility of FLG.

Published
2010

25. Ultrahigh dielectric permittivity in oxide ceramics by hydrogenation

Author

Duong, Nguyen Xuan, primary, Jang, Ji-Soo, additional, Jung, Min-Hyoung, additional, Bae, Jong-Seong, additional, Ahn, Chang Won, additional, Jin, Jong Sung, additional, Ihm, Kyuwook, additional, Kim, Gyehyeon, additional, Lim, So Yeon, additional, Lee, Jongmin, additional, Dung, Dang Duc, additional, Lee, Soonil, additional, Kim, Young-Min, additional, Lee, Sanghan, additional, Yang, Sang Mo, additional, Sohn, Changhee, additional, Kim, Ill Won, additional, Jeong, Hu Young, additional, Baek, Seung-Hyub, additional, and Kim, Tae Heon, additional

Published
2023
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28. High-energy P2-type Na-layered oxide cathode with sequentially occurred anionic redox and suppressed phase transition

Author

Lee, Sangyeop, primary, Kang, Jungmin, additional, Cho, Min-kyung, additional, Park, Hyunyoung, additional, Ko, Wonseok, additional, Lee, Yongseok, additional, Ahn, Jinho, additional, Lee, Seokjin, additional, Sim, Eunji, additional, Ihm, Kyuwook, additional, Hong, Jihyun, additional, Kim, Hyungsub, additional, and Kim, Jongsoon, additional

Published
2022
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30. One-Step Passivation of Both Sulfur Vacancies and SiO2Interface Traps of MoS2Device

Author

Ahn, Byungwook, Kim, Yoonsok, Kim, Meeree, Yu, Hyang Mi, Ahn, Jaehun, Sim, Eunji, Ji, Hyunjin, Gul, Hamza Zad, Kim, Keun Soo, Ihm, Kyuwook, Lee, Hyoyoung, Kim, Eun Kyu, and Lim, Seong Chu

Abstract

Transition metal dichalcogenides (TMDs) benefit electrical devices with spin–orbit coupling and valley- and topology-related properties. However, TMD-based devices suffer from traps arising from defect sites inside the channel and the gate oxide interface. Deactivating them requires independent treatments, because the origins are dissimilar. This study introduces a single treatment to passivate defects in a multilayer MoS2FET. By applying back-gate bias, protons from an H–TFSI droplet are injected into the MoS2, penetrating deeply enough to reach the SiO2gate oxide. The characterizations employing low-temperature transport and deep-level transient spectroscopy (DLTS) studies reveal that the trap density of S vacancies in MoS2drops to the lowest detection level. The temperature-dependent mobility plot on the SiO2substrate resembles that of the h-BN substrate, implying that dangling bonds in SiO2are passivated. The carrier mobility on the SiO2substrate is enhanced by approximately 2200% after the injection.

Published
2023
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31. Occurrence of anionic redox with absence of full oxidation to Ru5+in high-energy P2-type layered oxide cathode

Author

Ahn, Jinho, Park, Hyunyoung, Ko, Wonseok, Lee, Yongseok, Kang, Jungmin, Lee, Seokjin, Lee, Sangyeop, Sim, Eunji, Ihm, Kyuwook, Hong, Jihyun, Yoo, Jung-Keun, Ku, Kyojin, and Kim, Jongsoon

Abstract

We report that the anionic redox can occur in Ru-based layered-oxide-cathodes before full oxidation of Ru4+/Ru5+. Combining studies using first-principles calculation and experimental techniques reveals that further Na+deintercalation from P2-Na0.33[Mg0.33Ru0.67]O2is based on anionic oxidation after 0.33 mol Na+deintercalation from P2-Na0.67[Mg0.33Ru0.67]O2with cationic oxidation of Ru4+/Ru4.5+.

Published
2023
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33. Robust Room Temperature Ferromagnetism In Cobalt Doped Graphene by Precision Control of Metal Ion Hybridization.

Author

Paidi, Vinod K, Jung, Euiyeon, Lee, Jaewoo, Lee, Alex Taekyung, Shepit, Michael, Ihm, Kyuwook, Lee, Byoung‐Hoon, van Lierop, Johan, Hyeon, Taeghwan, and Lee, Kug‐Seung

Subjects
FERROMAGNETISM, GRAPHENE, ORBITAL hybridization, METAL ions, MAGNETIC materials
Abstract

Graphene‐based magnetic materials exhibit novel properties and promising applications in the development of next‐generation spintronic devices. Modern synthesis techniques have paved the way to design precisely the local environments of metal atoms anchored onto a nitrogen‐doped graphene matrix. Herein, it is demonstrated that grafting cobalt (Co) into the graphene lattice induces robust and stable room‐temperature ferromagnetism. These comprehensive experiments and first‐principles calculations unambiguously identify that the mechanism for this unusual ferromagnetism is π‐d orbital hybridization between Co dxz and graphene pz orbitals. Here, it is found that the magnetic interactions of Co–carbon ions are mediated by the spin‐polarized graphene pz orbitals, and room temperature ferromagnetism can be stabilized by electron doping. It is also found that the electronic structure near the Fermi level, which sets the nature of spin polarization of graphene pz bands, strongly depends on the local environment of the Co moiety. This is the crucial, previously missing, ingredient that enables control of the magnetism. Overall, these observations unambiguously reveal that engineering the atomic structure of metal‐embedded graphene lattices through careful d to p orbital interactions opens a new window of opportunities for developing graphene‐based spintronics devices. [ABSTRACT FROM AUTHOR]

Published
2023
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34. Extreme Enhancement of Carbon Hydrogasification via Mechanochemistry

Author

Han, Gao‐Feng, primary, Zhang, Peng, additional, Scholzen, Pascal, additional, Noh, Hyuk‐Jun, additional, Yang, Mihyun, additional, Kweon, Do Hyung, additional, Jeon, Jong‐Pil, additional, Kim, Young Hyun, additional, Kim, Seong‐Wook, additional, Han, Sun‐Phil, additional, Andreev, Andrey S., additional, Lang, Guillaume, additional, Ihm, Kyuwook, additional, Li, Feng, additional, d'Espinose de Lacaillerie, Jean‐Baptiste, additional, and Baek, Jong‐Beom, additional

Published
2022
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36. Hybrid Materials Research Center, Department of Nanotechnology and Advanced Materials Engineering & Sejong Battery Institute, Sejong University, 98 Gunja-Dong, Gwangjin-Gu, Seoul 05006, South Korea

Author

Jo, Jae Hyeon, primary, KIm, Hee Jae, additional, Yaqoob, Najma, additional, Ihm, Kyuwook, additional, Guillon, Olivier, additional, Sohn, Kee-Sun, additional, Lee, Naesung, additional, Kaghazchi, Payam, additional, and Myung, Seung-Taek, additional

Published
2022
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40. Template Engineering of Metal-to-Insulator Transitions in Epitaxial Bilayer Nickelate Thin Films

Author

Lee, Jongmin, primary, Kim, Gi-Yeop, additional, Jeong, Seyeop, additional, Yang, Mihyun, additional, Kim, Jong-Woo, additional, Cho, Byeong-Gwan, additional, Choi, Yongseong, additional, Kim, Sangmo, additional, Choi, Jin San, additional, Lee, Tae Kwon, additional, Kim, Jiwoong, additional, Lee, Dong Ryeol, additional, Chang, Seo Hyoung, additional, Park, Sungkyun, additional, Jung, Jong Hoon, additional, Bark, Chung Wung, additional, Koo, Tae-Young, additional, Ryan, Philip J., additional, Ihm, Kyuwook, additional, Kim, Sanghoon, additional, Choi, Si-Young, additional, Kim, Tae Heon, additional, and Lee, Sanghan, additional

Published
2021
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41. Bi doping stimulation on the visible-light absorption of In2O3 ceramics

Author

Kim, Jiwoong, primary, Park, Hongjun, additional, Kim, Doukyun, additional, Yang, Seojin, additional, Song, Sehwan, additional, Choi, Yesul, additional, Kim, Hyegyeong, additional, Bae, Jong-Seong, additional, Tam Le, Chinh, additional, Kim, Yong Soo, additional, Yang, Mihyun, additional, Ihm, Kyuwook, additional, Lee, Kug-Seung, additional, Park, Chul-Hong, additional, and Park, Sungkyun, additional

Published
2021
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42. Modulation of optical and electrical properties in hexagonal boron nitride by defects induced via oxygen plasma treatment

Author

Na, Youn Sung, primary, Kim, Jong Hun, additional, Kang, Sojung, additional, Jeong, Jae Hwan, additional, Park, Sunho, additional, Kim, Dae Hyun, additional, Ihm, Kyuwook, additional, Watanabe, Kenji, additional, Taniguchi, Takashi, additional, Kwon, Young-Kyun, additional, Kim, Young Duck, additional, and Lee, Gwan-Hyoung, additional

Published
2021
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45. Electrochemical Generation of Mesopores and Residual Oxygen for the Enhanced Activity of Silver Electrocatalysts

Author

Mohanty, Sangram Keshari, primary, Kim, Sol Jin, additional, Kim, Ji Su, additional, Lim, Yun Ji, additional, Kim, Sanghyeok, additional, Yang, Mihyun, additional, Park, Youchang, additional, Jeong, Jiung, additional, Ihm, Kyuwook, additional, Cho, Sung Ki, additional, Park, Kang Hyun, additional, Shin, Heon Cheol, additional, Lee, Hosik, additional, Nam, Ki Min, additional, and Yoo, Hyun Deog, additional

Published
2021
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