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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>
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>
Size와 Taper가 ProFile과 Hyflex CM Ni-Ti 파일의 기계적 물성 변화에 미치는 효과
이형우(Hyungwoo Lee),이창하(Chang-ha Lee),이인복(In-bog Lee) 대한치과재료학회 2022 대한치과재료학회지 Vol.49 No.1
The purpose of this study was to investigate the effect of size and taper on the mechanical properties of two Ni-Ti files. A controlled memory Ni-Ti file, Hyflex CM (Coltène-Whaledent, Altstätten, Switzerland) and a conventional Ni-Ti file, ProFile (Dentsply Maillefer, Ballaigues, Switzerland) were used. The size and taper (sizer/taper values) were 20/.04, 25/.04, 25/.06 and 30/.04. The U-Mechanics Analyser (IB Systems, Seoul, Korea) was used to measure the bending, torsional, and fatigue fracture resistance of the files (n=5). ProFile showed elastic deformation, but Hyflex CM showed higher hysteresis with plastic deformation in bending resistance test. The bending and torsional resistance of ProFile increased with increasing size and taper, though the #25 and #30 files of Hyflex CM did not resulted in any change. Hyflex CM showed greater fatigue fracture resistance than ProFile in all sizes and tapers. Without considering root canal excavation efficiency, it is considered that Hyflex CM has better root canal trackability and fewer fatigue fractures than ProFile.
Wide Contact Structures for Low-Noise Nanochannel Devices Based on a Carbon Nanotube Network
Lee, Hyungwoo,Lee, Minbaek,Namgung, Seon,Hong, Seunghun American Chemical Society 2010 ACS NANO Vol.4 No.12
<P/><P>We have developed a wide contact structure for low-noise nanochannel devices based on a carbon nanotube (CNT) network. This low-noise CNT network-based device has a dumbbell-shaped channel, which has wide CNT/electrode contact regions and, in effect, reduces the contact noise. We also performed a systematic analysis of structured CNT networks and established an empirical formula that can explain the noise behavior of arbitrary-shaped CNT network-based devices including the effect of contact regions and CNT alignment. Interestingly, our analysis revealed that the noise amplitude of <I>aligned</I> CNT networks behaves quite differently compared with that of <I>randomly oriented</I> CNT networks. Our results should be an important guideline in designing low-noise nanoscale devices based on a CNT network for various applications such as a highly sensitive low-noise sensor.</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>
Nanoscale Direct Mapping of Noise Source Activities on Graphene Domains
Lee, Hyungwoo,Cho, Duckhyung,Shekhar, Shashank,Kim, Jeongsu,Park, Jaesung,Hong, Byung Hee,Hong, Seunghun American Chemical Society 2016 ACS NANO Vol.10 No.11
<P>An electrical noise is one of the key parameters determining the performance of modern electronic devices. However, it has been extremely difficult, if not impossible, to image localized noise sources or their activities in such devices. We report a 'noise spectral imaging' strategy to map the activities of localized noise sources in graphene domains. Using this method, we could quantitatively estimate sheet resistances and noise source densities inside graphene domains, on domain boundaries and on the edge of graphene. The results show high activities of noise sources and large sheet resistance values at the domain boundary and edge of graphene. Additionally, we showed that the top layer in double layer graphene had lower noises than single-layer graphene. This work provides valuable insights about the electrical noises of graphene. Furthermore, the capability to directly map noise sources in electronic channels can be a major breakthrough in electrical noise research in general.</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>