Search

Your search keyword '"Lee, June Ho"' showing total 171 results
Start Over Author "Lee, June Ho"
171 results on '"Lee, June Ho"'

3. Electron-Hole Separation in Ferroelectric Oxides for Efficient Photovoltaic Responses

Author

Kim, Donghoon, Han, Hyeon, Lee, June Ho, Grossman, Jeffrey C., Kim, Donghun, and Jang, Hyun Myung

Subjects
Condensed Matter - Materials Science
Abstract

Despite their potential to exceed the theoretical Shockley-Queisser limit, ferroelectric photovoltaics (FPVs) have performed inefficiently due to their extremely low photocurrents. Incorporating Bi2FeCrO6 (BFCO) as the light absorber in FPVs has recently led to impressively high and record photocurrents [Nechache et al. Nature Photon. 2015, 9, 61], reviving the FPV field. However, our understanding of this remarkable phenomenon is far from satisfactory. Here, we use first-principles calculations to determine that such excellent performance mainly lies in the efficient separation of electron-hole (e-h) pairs. We show that photoexcited electrons and holes in BFCO are spatially separated on the Fe and Cr sites, respectively. This separation is much more pronounced in disordered BFCO phases, which show exceptional PV responses. We further set out to design a strategy for next-generation FPVs, not limited to BFCO, by exploring 44 additional Bi-based double-perovskite oxides. We suggest 9 novel active-layer materials that can offer strong e-h separations and a desired band gap energy for application in FPVs. Our work indicates that charge separation is the most important issue to be addressed for FPVs to compete with conventional devices., Comment: 33 pages, 5 main figures, 5 supporting figures

Published
2017
Full Text
View/download PDF

4. Two Distinct Modes of Hydrogen-Bonding Interaction in the Prototypic Hybrid Halide Perovskite, Tetragonal CH3NH3PbI3

Author

Lee, June Ho, Lee, Jung-Hoon, Kong, Eui-Hyun, and Jang, Hyun M.

Subjects
Condensed Matter - Materials Science
Abstract

In spite of the key role of hydrogen bonding in the structural stabilization of the prototypic hybrid halide perovskite, CH3NH3PbI3 (MAPbI3), little progress has been made in our in-depth understanding of the hydrogen-bonding interaction between the MA+-ion and the iodide ions in the PbI6-octahedron network. Herein, we show that there exist two distinct types of the hydrogen-bonding interaction, naming a- and b-modes, in the tetragonal MAPbI3 on the basis of symmetry argument and density-functional theory calculations. The computed Kohn-Sham (K-S) energy difference between these two interaction modes is 45.14 meV per MA-site with the a-interaction mode being responsible for the stable hydrogen-bonding network. We have further estimated the individual bonding strength for the ten relevant hydrogen bonds having a bond critical point. The net difference in the total hydrogen-bonding energies between these two interaction modes is 43.87 meV per MA-site, which nearly coincides with the K-S energy difference of 45.14 meV., Comment: 39 pages

Published
2015

12. Feasibility of Space Charge Measurements on HVDC Cable Joints: Study Group—IEEE DEIS Technical Committee “HVDC Cable and Systems:”

Author

Tzimas, Antonios, primary, Diban, Bassel, additional, Boyer, Ludovic, additional, Chen, George, additional, Castellon, Jerome, additional, Chitiris, Nathanail, additional, Fothergill, John, additional, Hozumi, Naohiro, additional, Kim, Yoonhyoung, additional, Lee, June-Ho, additional, Mauseth, Frank, additional, Mazzanti, Giovanni, additional, Morshuis, Peter, additional, Troia, Ivan, additional, Tanaka, Yasuhiro, additional, and Wu, Kai, additional

Published
2022
Full Text
View/download PDF

19. First-Principles Investigations on the Semiconductor-to-Metal Phase Transition of 2D Si2Te3for Reversible Resistive Switching

Author

Kim, Jaeseon, Lee, June Ho, Kim, Seong Hun, Park, Youngjun, Jeong, Unyong, and Lee, Donghwa

Abstract

Si2Te3is attracting attention due to its compatibility with Si technology while still showing advantages as a two-dimensional layered material. Although recent experimental studies have observed the resistive switching process in Si2Te3-based memristors, the mechanism has not been clearly identified. In this study, first-principles density functional theory calculations are employed to understand the relationship between the phase transition of Si2Te3and the reversible resistive switching of the Si2Te3-based memristor. Our calculation results show that although semiconducting Si2Te3is energetically more stable than two metallic Si2Te3phases (α and β), two metallic Si2Te3can be energetically stabilized by excess holes. The enhanced energetic preference of two metallic Si2Te3by excess holes is explained by the reduced occupation of antibonding states between Si and Te. Our study finds that the energy barrier for the phase transition between semiconducting Si2Te3and α-metallic Si2Te3varies significantly by excess charge carriers so the phase transition can be directly connected to the reversible resistive switching of the Si2Te3-based memristor under external bias. Our finding will serve as a cornerstone for optimizing the resistive switching process of the Si2Te3-based memristor.

Published
2023
Full Text
View/download PDF

24. Accuracy improvement in peak positioning of spectrally distorted fiber Bragg grating sensors by Gaussian curve fitting

Author

Lee, Hyun-Wook, Park, Hyoung-Jun, Lee, June-Ho, and Song, Minho

Subjects
Diffraction gratings -- Analysis, Diffraction gratings -- Spectra, Gaussian processes -- Analysis, Fiber optics -- Analysis, Fiber optics, Astronomy, Physics
Abstract

To improve measurement accuracy of spectrally distorted fiber Bragg grating temperature sensors, reflection profiles were curve fitted to Gaussian shapes, of which center positions were transformed into temperature information. By applying the Gaussian curve-fitting algorithm in a tunable bandpass filter demodulation scheme, ~0.3 [degrees]C temperature resolution was obtained with a severely distorted grating sensor, which was much better than that obtained using the highest peak search algorithm. A binary search was also used to retrieve the optimal fitting curves with the least amount of processing time. OCIS codes: 120.0120, 120.2230, 060.2300.

Published
2007

29. Electron−hole separation in ferroelectric oxides for efficient photovoltaic responses

Author

Massachusetts Institute of Technology. Department of Materials Science and Engineering, Grossman, Jeffrey C., Kim, Donghoon, Han, Hyeon, Lee, June Ho, Choi, Jin Woo, Jang, Hyun Myung, Kim, Donghun, Massachusetts Institute of Technology. Department of Materials Science and Engineering, Grossman, Jeffrey C., Kim, Donghoon, Han, Hyeon, Lee, June Ho, Choi, Jin Woo, Jang, Hyun Myung, and Kim, Donghun

Abstract

Despite their potential to exceed the theoretical Shockley−Queisser limit, ferroelectric photovoltaics (FPVs) have performed inefficiently due to their extremely low photocurrents. Incorporating Bi₂FeCrO₆(BFCO) as the light absorber in FPVs has recently led to impressively high and record photocurrents [Nechache R, et al. (2015) Nat Photonics 9:61–67], which has revived the FPV field. However, our understanding of this remarkable phenomenon is far from satisfactory. Here, we use first-principles calculations to determine that such excellent performance mainly lies in the efficient separation of electron− hole (e-h) pairs. We show that photoexcited electrons and holes in BFCO are spatially separated on the Fe and Cr sites, respectively. This separation is much more pronounced in disordered BFCO phases, which adequately explains the observed exceptional PV responses. We further establish a design strategy to discover next-generation FPV materials. By exploring 44 additional Bi-based double-perovskite oxides, we suggest five active-layer materials that offer a combination of strong e-h separations and visible-light absorptions for FPV applications. Our work indicates that charge separation is the most important issue to be addressed for FPVs to compete with conventional devices. Keywords: ferroelectrics; double perovskites; photovoltaics; e-h separation; density functional theory

Published
2019

31. Effect of oxygen vacancies on electrical conductivity of La0.5Sr0.5FeO3−δ from first-principles calculations.

Author

Shin, Yonghun, Doh, Kyung-Yeon, Kim, Seong Hun, Lee, June Ho, Bae, Hohan, Song, Sun-Ju, and Lee, Donghwa

Abstract

We use first-principles density functional theory calculations to understand how oxygen vacancies degrade the electrical conductivity of mixed ionic-electronic conductor (MIEC) at low oxygen partial pressure (PO2). Analysis focused on La0.5Sr0.5FeO3−δ, which shows the highest mixed conductivity among cobalt-free iron-based perovskite oxides. Calculation results show that hole compensation by electrons released from oxygen vacancies lowers the electrical conductivity and eventually leads to metal-to-semiconductor transition at low PO2. Analyses of effective mass change and charge-density show that holes are the major charge carrier of electrical conductivity, but the contribution of electrons to conductivity increases as temperature increases. We suggest several possible ways to reduce the degradation of electrical conductivity at low PO2. Our results provide guidelines to design highly effective oxygen-selective membranes. [ABSTRACT FROM AUTHOR]

Published
2020
Full Text
View/download PDF

50. Combined Anomaly of Intramedullary Arteriovenous Malformation and Lipomyelomeningocele

Author

Lee, June Ho, Chung, Chun Kee, Choe, Gheeyoung, Chi, Je G., Chang, Kee-Hyun, and Kim, Hyun Jib

Subjects
Adult, Arteriovenous Malformations, Male, Meningomyelocele, Spinal Cord, Sacrococcygeal Region, Angiography, Humans, Lipoma, Spinal Cord Neoplasms, Magnetic Resonance Imaging, Spine
Abstract

Summary: We report a rare situation in which a lipomyelomeningocele and an intramedullary arteriovenous malformation (AVM) occurred together at the T11–L1 level in a 44-year-old man. MR images showed a hypervascular lesion intradurally and a fatty component extradurally. Spinal angiography revealed this lesion to be an intramedullary AVM with multiple feeding arteries from the right T12 and left T10 intercostal artery and the left L1 lumbar artery, drained by tortuous, dilated, perimedullary veins.

Published
2000

Catalog

Books, media, physical & digital resources
See catalog results