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Lee, Minbaek,Lee, Joohyung,Kim, Tae Hyun,Lee, Hyungwoo,Lee, Byung Yang,Park, June,Jhon, Young Min,Seong, Maeng-Je,Hong, Seunghun IOP Pub 2010 Nanotechnology Vol.21 No.5
<P>Nanoscale sensors based on single-walled carbon nanotube (SWNT) networks have been considered impractical due to several fundamental limitations such as a poor sensitivity and small signal-to-noise ratio. Herein, we present a strategy to overcome these fundamental problems and build highly-sensitive low-noise nanoscale sensors simply by controlling the structure of the SWNT networks. In this strategy, we prepared nanoscale width channels based on aligned SWNT networks using a directed assembly strategy. Significantly, the aligned network-based sensors with narrower channels exhibited even better signal-to-noise ratio than those with wider channels, which is opposite to conventional random network-based sensors. As a proof of concept, we demonstrated 100 nm scale low-noise sensors to detect mercury ions with the detection limit of ∼1 pM, which is superior to any state-of-the-art portable detection system and is below the allowable limit of mercury ions in drinking water set by most government environmental protection agencies. This is the first demonstration of 100 nm scale low-noise sensors based on SWNT networks. Considering the increased interests in high-density sensor arrays for healthcare and environmental protection, our strategy should have a significant impact on various industrial applications. </P>
Real-time detection of chlorine gas using Ni/Si shell/core nanowires
Lee, Dong-Jin,Heo, Kwang,Lee, Hyungwoo,Jin, Joon-Hyung,Chang, Hochan,Park, Minjun,Lee, Han-Bo-Ram,Kim, Hyungjun,Lee, Byung Yang Springer US 2015 NANOSCALE RESEARCH LETTERS Vol.10 No.1
<P>We demonstrate the selective adsorption of Ni/Si shell/core nanowires (Ni-Si NWs) with a Ni outer shell and a Si inner core on molecularly patterned substrates and their application to sensors for the detection of chlorine gas, a toxic halogen gas. The molecularly patterned substrates consisted of polar SiO<SUB>2</SUB> regions and nonpolar regions of self-assembled monolayers of octadecyltrichlorosilane (OTS). The NWs showed selective adsorption on the polar SiO<SUB>2</SUB> regions, avoiding assembly on the nonpolar OTS regions. Utilizing these assembled Ni-Si NWs, we demonstrate a sensor for the detection of chlorine gas. The utilization of Ni-Si NWs resulted in a much larger sensor response of approximately 23% to 5 ppm of chlorine gas compared to bare Ni NWs, due to the increased surface-to-volume ratio of the Ni-Si shell/core structure. We expect that our sensor will be utilized in the future for the real-time detection of halogen gases including chlorine with high sensitivity and fast response.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s11671-015-0729-2) contains supplementary material, which is available to authorized users.</P>
Graphene–nanowire hybrid structures for high-performance photoconductive devices
Lee, Hyungwoo,Heo, Kwang,Park, Jaesung,Park, Yongju,Noh, Seunguk,Kim, Kwang S.,Lee, Changhee,Hong, Byung Hee,Jian, Jikang,Hong, Seunghun The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.17
<P>Graphene–CdS nanowire (NW) hybrid structures with high-speed photoconductivity were developed. The hybrid structure was comprised of CdS NWs which were selectively grown in specific regions on a single-layer graphene sheet. The photoconductive channels based on graphene–CdS NW hybrid structures exhibited much larger photocurrents than graphene-based channels and much faster recovery speed than CdS NW network-based ones. Our graphene–CdS NW structures can be useful because they were much faster than commercial CdS film-based photodetectors and had photocurrents large enough for practical applications.</P> <P>Graphic Abstract</P><P>We have developed a photoconductive channel based on graphene–CdS nanowire hybrid structures which exhibited large photocurrent and fast recovery speed. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm16565a'> </P>
First-principles study of two dimensional magnetic oxides
Hyungwoo Lee,Minseok Choi 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
Two-dimensional (2D) transition materials have been attracted attention since they are not only ideal platforms to investigate exotic physical phenomena but also are technically promising for applications. According to Mermin-Wagner theorem, long-range magnetic order is unstable in 2D system due to thermal fluctuation. However, magnetic anisotropy can remove this restriction and stabilize the long-range magnetic order in 2D system. In this talk, we present a first principle study of the magnetic ordering in 2D magnetic oxides. Spin-orbit coupling and the Hubbard-U scheme were employed. Several 2D magnetic configurations including 120˚ Néel configuration were considered, and stable crystal and electronic structure of the oxides were found at each magnetic configuration. In addition, strain effect on magnetic anisotropy was examined.
Lee, Hyungwoo,Jang, Hyoik,Choi, Youn A,Kim, Hyung Chan,Chung, Hyewon Association for Research in Vision and Ophthalmolo 2018 Investigative ophthalmology & visual science Vol.59 No.2
<P>CONCLUSIONS. DME patients with diffuse edema exhibit higher sCD14 levels in the AH and more HF in the inner retina than patients with focal edema, indicating severe inflammation. The strong correlation between sCD14 and HF in the inner retina suggests that the HF observed on SD-OCT may be due to activated microglia in DME.</P>
Hyungwoo Kim,Jangwon Lee,Jongsuh Lee,Jaeyub Hyun,Semyung Wang IEEE 2016 IEEE transactions on magnetics Vol.52 No.3
<P>In this paper, a magnetic resonator for wireless energy transfer system is designed using topology optimization based on an electromagnetic wave analysis. To analyze the magnetic resonator, the finite-difference time-domain method in a 2-D transverse magnetic mode is used with a Gaussian pulse source and perfectly matched layers. The topology optimization using solid isotropic material with the penalization method of a magnetic resonator is conducted to maximize magnetic energy. After these approaches, the fast Fourier transform is used to obtain the response of the magnetic resonator system over a wide range of frequencies.</P>