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88 results on '"Cho, Jung-Woo"'

51. Conditional radiation tolerance of ferroelectric Hf0.5Zr0.5O2 thin film under 60Co gamma-ray irradiation.

Author

Namkung, Jin, Song, Myeong Seop, Lee, Kyu Cheol, Lee, Kyoungjun, Cho, Jung Woo, and Chae, Seung Chul

Subjects
RADIATION tolerance, FERROELECTRIC thin films, THIN films, IRRADIATION, ELECTRIC fields
Abstract

We report the effect of 60Co gamma-ray irradiation on the ferroelectric properties of metal–ferroelectric Hf0.5Zr0.5O2–metal thin film structures. The pristine Hf0.5Zr0.5O2 films showed strong radiation tolerance against gamma-rays with stable remanant polarization values. When Hf0.5Zr0.5O2 films were exposed to electric field cycling, or "wake-up" process, prior to irradiation, however, their ferroelectricity demonstrated a clear degradation of remanant polarization and coercive voltage shift of the hysteresis curves. The analysis of ferroelectric switching dynamics revealed faster polarization switching with broadening of Lorentzian distribution of characteristic switching time for higher radiation doses, which is contrary to the wake-up behavior. The relationship between the wake-up process and gamma-ray irradiation on the stability of ferroelectric Hf0.5Zr0.5O2 films was discussed in light of domain alignment and defect mechanisms, considering both the redistribution and trapping of defect charges. [ABSTRACT FROM AUTHOR]

Published
2022
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60. Atomic-Scale Scanning of Domain Network in the Ferroelectric HfO2Thin Film

Author

Park, Kunwoo, Kim, Dongmin, Lee, Kyoungjun, Lee, Hyun-Jae, Kim, Jihoon, Kang, Sungsu, Lin, Alex, Pattison, Alexander J., Theis, Wolfgang, Kim, Chang Hoon, Choi, Hyesung, Cho, Jung Woo, Ercius, Peter, Lee, Jun Hee, Chae, Seung Chul, and Park, Jungwon

Abstract

Ferroelectric HfO2-based thin films have attracted much interest in the utilization of ferroelectricity at the nanoscale for next-generation electronic devices. However, the structural origin and stabilization mechanism of the ferroelectric phase are not understood because the film is typically nanocrystalline with active yet stochastic ferroelectric domains. Here, electron microscopy is used to map the in-plane domain network structures of epitaxially grown ferroelectric Y:HfO2films in atomic resolution. The ferroelectricity is confirmed in free-standing Y:HfO2films, allowing for investigating the structural origin for their ferroelectricity by 4D-STEM, high-resolution STEM, and iDPC-STEM. At the grain boundaries of <111>-oriented Pca21orthorhombic grains, a high-symmetry mixed-(R3m, Pnm21) phase is induced, exhibiting enhanced polarization due to in-plane compressive strain. Nanoscale Pca21orthorhombic grains and their grain boundaries with mixed-(R3m, Pnm21) phases of higher symmetry cooperatively determine the ferroelectricity of the Y:HfO2film. It is also found that such ferroelectric domain networks emerge when the film thickness is beyond a finite value. Furthermore, in-plane mapping of oxygen positions overlaid on ferroelectric domains discloses that polarization is suppressed at vertical domain walls, while it is active when domains are aligned horizontally with subangstrom domain walls. In addition, randomly distributed 180° charged domain walls are confined by spacer layers.

Published
2024
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63. Optimal button arrangement of a percussion drill bit and its operating condition for improving drilling efficiency.

Author

Kang, Hoon, Park, Jin-Young, Cho, Jung-Woo, Jang, Jin-Seok, Kim, Kun-Woo, and Lee, Jae-Wook

Abstract

This paper proposes an optimal button arrangement of a percussion drill bit and its operating condition to improve drilling efficiency. A new evaluation method is introduced for the button arrangement that utilizes the superimposed impact area, blank area, and drilling deviation moment as the quantitative indices to evaluate the impact of buttons on the rock surface. To determine the optimal button arrangement and its operating conditions, a progressive metamodel-based design optimization was conducted using the new evaluation indices as the analysis response, and then the optimal solution was determined through iteration. Consequently, all the button evaluation indices were reduced significantly and the impact areas were distributed uniformly under a specific operating condition. Additionally, the drilling performances of the optimal button arrangement were investigated according to the operating conditions to obtain the maximum drilling performance in terms of the drilling machine operation. [ABSTRACT FROM AUTHOR]

Published
2018
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75. Computational fluid dynamics simulations to optimize the filling of an underground mine cavity with fly ash

Author

Song, Changheon, Kim, Daeji, Kang, Hoon, Cho, Min-Gi, Park, Jin-Young, Cho, Jung-Woo, and Lee, Sang-Eun

Abstract

AbstractSubsidence caused by the underground spaces of abandoned mines is a potential danger to life and property. This study focuses on optimizing the filling of these cavities at a site in Korea to prevent subsidence and to reuse abandoned mine. Fly ash produced from thermoelectric power plants might be profitably used to fill the abandoned workings. Computational fluid dynamics (CFD) is used here to simulate fly ash injection into mine cavities by a volume-of-fluid method. The numerical experiments are run after the establishment of three input parameters, which are used to optimize two output parameters. This series of CFD simulations investigates the effects of filling with respect to the operation factors of the filling method. The filling operation is then optimized with regard to efficiency and equipment cost. A low injection point with drilling connection of vertical shafts gives the most efficient filling of underground mine cavities.

Published
2017
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80. Fabrication of an all‐layer‐printed TFT‐LCD device via large‐area UV imprinting lithography

Author

Lee, Seung Jun, primary, Park, Dae‐Jin, additional, Bae, Joo Han, additional, Lee, Sung Hee, additional, Kim, Jangkyum, additional, Kim, Kyuyoung, additional, Bae, Jungmok, additional, Kim, Bo Sung, additional, Lim, Soonkwon, additional, Lee, Sukwon, additional, Kwon, Sin, additional, Seo, Jungwoo, additional, Kim, Kihyun, additional, Cho, Jung‐woo, additional, and Chang, Jaehyuk, additional

Published
2010
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84. EXTENDED ABSTRACTS: 7. ROCK PROPERTIES – 7.2. In-Situ and Laboratory Tests

Author

CHEON, D. S., primary, PARK, C., additional, JUNG, Y. B., additional, JEON, S., additional, CHO, JUNG-WOO, additional, KIM, HO-YOUNG, additional, JEON, SEOKWON, additional, DUBEY, R. K., additional, ITAKURA, KEN-ICHI, additional, TOMITA, SHINJI, additional, IGUCHI, SHOZO, additional, ICHIHARA, YOSHIHISA, additional, MASTALIR, PETER, additional, BERGNER, TOM, additional, COYTE, CHRIS, additional, KANG, S. S., additional, KOKAJI, S., additional, HIRATA, A., additional, KO, T. Y., additional, KEMENY, J., additional, KUMAR, AJIT, additional, SAMADHIYA, N. K., additional, SINGH, MAHENDRA, additional, LI, HUI, additional, CHEN, GANG, additional, LIANG, W., additional, YANG, C., additional, ZHAO, Y., additional, DUSSEAULT, M. B., additional, GHAROUNI-NIK, M., additional, HASHEMI, S., additional, ONISHI, K., additional, ISHIKAWA, Y., additional, OKAMOTO, K., additional, XUE, Z., additional, YAMADA, Y., additional, MATSUOKA, T., additional, PETROŠ, V., additional, ŠANCER, J., additional, MICHALČÍK, P., additional, XIE, QIANG, additional, YU, XIANBIN, additional, DA GAMA, CARLOS DINIS, additional, NA, YUKANG, additional, ZHANG, YONGXING, additional, XING, H. F., additional, LI, Q. B., additional, LIU, Z. H., additional, YE, G. B., additional, XU, C., additional, YAN, Z. G., additional, ZHU, H. H., additional, YANG, L. D., additional, YAN, X. B., additional, LI, Y., additional, ZHANG, X. X., additional, and YAZDANI, M., additional

Published
2006
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86. Optimum spacing of TBM disc cutters: a numerical simulation using the three-dimensional dynamic fracturing method.

Author

Cho Jung-Woo, Chang Soo-Ho., Jeon Seokwon, Yu Sang-Hwa, Cho Jung-Woo, Chang Soo-Ho., Jeon Seokwon, and Yu Sang-Hwa

Abstract

Numerical modelling was carried out to simulate rock fragmentation by tunnel-boring-machine disc cutters. The AUTODYN-3D code was used to simulate the three-dimensional dynamic failure observed in linear cutting machine (LCM) tests. The mean rolling force and the mass of rock debris determined from the numerical results were used to calculate the specific energy, defined as the energy required to cut through a unit volume of rock. The effects of cutter speed and model size on the variation in specific energy were studied before carrying out the main simulations to determine optimum cutter spacing. LCM tests were performed numerically on models representing eight different types of Korean rock. For isotropic and homogeneous rocks the optimum cutter spacing obtained from the numerical simulations was in good agreement with those determined using the LCM tests. The simulations provided a realistic description of the rock fragmentation mechanism and also yielded quantitatively reliable values for the specific energy. The results show that numerical simulations using AUTODYN-3D may possibly be substituted for LCM tests for assessing the performance of a TBM., Numerical modelling was carried out to simulate rock fragmentation by tunnel-boring-machine disc cutters. The AUTODYN-3D code was used to simulate the three-dimensional dynamic failure observed in linear cutting machine (LCM) tests. The mean rolling force and the mass of rock debris determined from the numerical results were used to calculate the specific energy, defined as the energy required to cut through a unit volume of rock. The effects of cutter speed and model size on the variation in specific energy were studied before carrying out the main simulations to determine optimum cutter spacing. LCM tests were performed numerically on models representing eight different types of Korean rock. For isotropic and homogeneous rocks the optimum cutter spacing obtained from the numerical simulations was in good agreement with those determined using the LCM tests. The simulations provided a realistic description of the rock fragmentation mechanism and also yielded quantitatively reliable values for the specific energy. The results show that numerical simulations using AUTODYN-3D may possibly be substituted for LCM tests for assessing the performance of a TBM.

87. Atomic-Scale Scanning of Domain Network in the Ferroelectric HfO 2 Thin Film.

Author

Park K, Kim D, Lee K, Lee HJ, Kim J, Kang S, Lin A, Pattison AJ, Theis W, Kim CH, Choi H, Cho JW, Ercius P, Lee JH, Chae SC, and Park J

Abstract

Ferroelectric HfO 2 -based thin films have attracted much interest in the utilization of ferroelectricity at the nanoscale for next-generation electronic devices. However, the structural origin and stabilization mechanism of the ferroelectric phase are not understood because the film is typically nanocrystalline with active yet stochastic ferroelectric domains. Here, electron microscopy is used to map the in-plane domain network structures of epitaxially grown ferroelectric Y:HfO 2 films in atomic resolution. The ferroelectricity is confirmed in free-standing Y:HfO 2 films, allowing for investigating the structural origin for their ferroelectricity by 4D-STEM, high-resolution STEM, and iDPC-STEM. At the grain boundaries of <111>-oriented Pca2 1 orthorhombic grains, a high-symmetry mixed-( R 3 m , Pnm2 1 ) phase is induced, exhibiting enhanced polarization due to in-plane compressive strain. Nanoscale Pca2 1 orthorhombic grains and their grain boundaries with mixed-( R 3 m , Pnm2 1 ) phases of higher symmetry cooperatively determine the ferroelectricity of the Y:HfO 2 film. It is also found that such ferroelectric domain networks emerge when the film thickness is beyond a finite value. Furthermore, in-plane mapping of oxygen positions overlaid on ferroelectric domains discloses that polarization is suppressed at vertical domain walls, while it is active when domains are aligned horizontally with subangstrom domain walls. In addition, randomly distributed 180° charged domain walls are confined by spacer layers.

Published
2024
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88. Deterministic Orientation Control of Ferroelectric HfO 2 Thin Film Growth by a Topotactic Phase Transition of an Oxide Electrode.

Author

Lee K, Park K, Choi IH, Cho JW, Song MS, Kim CH, Lee JH, Lee JS, Park J, and Chae SC

Abstract

The scale-free ferroelectricity with superior Si compatibility of HfO 2 has reawakened the feasibility of scaled-down nonvolatile devices and beyond the complementary metal-oxide-semiconductor (CMOS) architecture based on ferroelectric materials. However, despite the rapid development, fundamental understanding, and control of the metastable ferroelectric phase in terms of oxygen ion movement of HfO 2 remain ambiguous. In this study, we have deterministically controlled the orientation of a single-crystalline ferroelectric phase HfO 2 thin film via oxygen ion movement. We induced a topotactic phase transition of the metal electrode accompanied by the stabilization of the differently oriented ferroelectric phase HfO 2 through the migration of oxygen ions between the oxygen-reactive metal electrode and the HfO 2 layer. By stabilizing different polarization directions of HfO 2 through oxygen ion migration, we can gain a profound understanding of the oxygen ion-relevant unclear phenomena of ferroelectric HfO 2 .

Published
2024
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