Search

Your search keyword '"Han, Jeong Woo"' showing total 1,036 results
Start Over Author "Han, Jeong Woo"
1,036 results on '"Han, Jeong Woo"'

1. Influence on extracted complex refractive index from phase inaccuracy of reflection-type THz-time-domain spectroscopy

Author

Han, Jeong Woo

Subjects
Physics - Optics
Abstract

Reflection-type terahertz (THz) time-domain spectroscopy (THz-TDS) enables the measurement of optical properties of opaque samples in the THz frequency range, e.g., carrier density and mobility. In this study, we examine the influence of phase inaccuracy on the extracted complex refractive index from reflection-type THz-TDS. Phase inaccuracy often arises from the placement mismatch between the perfect reflector, serving as the reference, and the target samples in reflection-type THz-TDS. By considering two representative systems, where free and bound carriers dominate optical properties, and introducing arbitrarily shifted placement mismatch, we confirm that significant errors in the extracted complex refractive index occur when the mismatch position exceeds 3 {\mu}m., Comment: 7 pages and 4 figures

Published
2024

2. Accuracy of extracted optical conductivity by Kramer-Kronig analysis from reflectivity spectrum

Author

Han, Jeong Woo

Subjects
Physics - Optics
Abstract

Kramers-Kronig (KK) analysis has been widely used to extract the optical conductivity spectrum from a broad range of reflectance spectrum obtained from far-infrared to ultraviolet frequency ranges. In this study, we present how measurement uncertainty in the reflectivity spectrum affects the extracted optical conductivity spectrum obtained through KK analysis. We consider realistic uncertainties that can easily occur in reflectance measurement environments: (1) a rigid shift of the absolute reflectance in the whole measurement frequency window, and (2) a linear decrement of reflectance with increasing frequency. Our investigation reveals that the reliability of the extracted optical conductivity spectrum, especially in the lower-frequency range, should be carefully addressed, particularly when the reflectance is above approximately 95 %., Comment: 7 pages with 3 figures

Published
2024

4. Atomic scale understanding of initial Cu-Ni oxidation from machine-learning accelerated first-principles simulations and in situ TEM experiments

Author

Wisesa, Pandu, Li, Meng, Curnan, Matthew T., Han, Jeong Woo, Yang, Judith C., and Saidi, Wissam A.

Subjects
Condensed Matter - Materials Science
Abstract

The development of accurate methods for determining how alloy surfaces spontaneously restructure under reactive and corrosive environments is a key, long-standing, grand challenge in materials science. Current oxidation models, such as Cabrera-Mott, are based on macroscopic empirical knowledge that lacks fundamental insight at the atomic level. Using machine learning-accelerated density functional theory with in situ environmental transmission electron microscopy (ETEM), we examine the interplay between surface reconstructions and preferential segregation tendencies of CuNi(100) surfaces under oxidation conditions. Our modeling approach based on molecular dynamics and grand canonical Monte Carlo simulations shows that oxygen-induced Ni segregation in CuNi alloy favors Cu(100)-O c(2x2) reconstruction and destabilizes the Cu(100)-O missing row reconstruction. The underpinnings of these stabilization tendencies are rationalized based on the similar atomic coordination and bond lengths in NiO rock salt and Cu(100)-O c(2x2) structures. In situ ETEM experiments show Ni segregation followed by NiO nucleation and growth in regions without MRR, with secondary nucleation and growth of Cu2O in MRR regions. This further corroborates the simulated surface oxidation and segregation modelling outcomes. Our findings are general and are expected to extend to other alloy systems.

Published
2023

5. Strong transient magnetic fields induced by THz-driven plasmons in graphene disks

Author

Han, Jeong Woo, Sai, Pavlo, But, Dmytro, Uykur, Ece, Winnerl, Stephan, Kumar, Gagan, Chin, Matthew L., Myers-Ward, Rachael L., Dejarld, Matthew T., Daniels, Kevin M., Murphy, Thomas E., Knap, Wojciech, and Mittendorff, Martin

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Optics
Abstract

Strong circularly polarized excitation opens up the possibility to generate and control effective magnetic fields in solid state systems, e.g., via the optical inverse Faraday effect or the phonon inverse Faraday effect. While these effects rely on material properties that can be tailored only to a limited degree, plasmonic resonances can be fully controlled by choosing proper dimensions and carrier concentrations. Plasmon resonances provide new degrees of freedom that can be used to tune or enhance the light-induced magnetic field in engineered metamaterials. Here we employ graphene disks to demonstrate light-induced transient magnetic fields from a plasmonic circular current with extremely high efficiency. The effective magnetic field at the plasmon resonance frequency of the graphene disks (3.5 THz) is evidenced by a strong (~1{\deg}) ultrafast Faraday rotation (~ 20 ps). In accordance with reference measurements and simulations, we estimated the strength of the induced magnetic field to be on the order of 0.7 T under a moderate pump fluence of about 440 nJ cm-2.

Published
2023
Full Text
View/download PDF

21. AWS: GNNs that Aggregate with Self-node Representation for Dehydrogenation Enthalpy Prediction

Author

Choi, Geonyeong, Yook, Hyunwoo, Han, Jeong Woo, Hong, Charmgil, Filipe, Joaquim, Editorial Board Member, Ghosh, Ashish, Editorial Board Member, Prates, Raquel Oliveira, Editorial Board Member, Zhou, Lizhu, Editorial Board Member, Nguyen, Ngoc Thanh, editor, Boonsang, Siridech, editor, Fujita, Hamido, editor, Hnatkowska, Bogumiła, editor, Hong, Tzung-Pei, editor, Pasupa, Kitsuchart, editor, and Selamat, Ali, editor

Published
2023
Full Text
View/download PDF

43. Charge Separation Induced by Asymmetric Surface Charge Effects in Quasi‐Solid State Electrolyte for Sustainable Anion Storage.

Author

Kim, Sungho, Kim, Dongjoo, Kim, Youngbi, Yang, Heejae, Lee, Hojung, Kang, Jieun, Han, Jihoon, Kim, Youn Soo, Ryu, Jaegeon, Han, Jeong Woo, and Park, Soojin

Subjects
POLYELECTROLYTES, POLYMER colloids, POWER density, STORAGE batteries, MONTMORILLONITE, KAOLINITE, SURFACE charges, HALLOYSITE
Abstract

Compared with conventional lithium‐ion battery systems, anion‐intercalation in graphite cathodes opens avenues for the development of batteries with groundbreaking power density. This study explores the enhancement of dual‐ion batteries (DIBs) by gel polymer electrolyte (GPE) enhanced with surface‐charged nanoclays, focusing on overcoming traditional challenges such as electrolyte decomposition, anion‐solvent co‐intercalation, and interfacial instability at the graphite cathode. Three nanoclays including montmorillonite, kaolinite, and halloysite are compared by incorporating them into GPE and evaluating their effect on the electrochemical properties, ion conduction, and mechanical integrity of DIBs. Particular attention is paid to the halloysite because of its differential internal and external surface charges, which generate charge separation, facilitate optimal lithium‐ion transport, and mitigate undesirable anion‐solvent interactions. These results indicate that halloysite‐incorporated GPE (HS‐G) significantly improves DIB performance, as demonstrated by extended cycle life, robust capacity retention at fast charge/discharge rates of 20 C, and operational stability over a wide temperature range (0–60 °C). These improvements are attributed to the unique structural advantages of HS‐G, including effective charge separation, enhanced anion diffusion, and reduced solvent co‐intercalation, which provide an environmentally friendly and cost‐effective approach to advanced DIB applications. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results