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Nonvolatile Memory Devices Prepared from Sol–Gel Derived Niobium Pentoxide Films
Baek, Hyunhee,Lee, Chanwoo,Choi, Jungkyu,Cho, Jinhan American Chemical Society 2013 Langmuir Vol.29 No.1
<P>We report on the resistive switching nonvolatile memory (RSNM) properties of niobium pentoxide (Nb<SUB>2</SUB>O<SUB>5</SUB>) films prepared using sol–gel chemistry. A sol–gel derived solution of niobium ethoxide, a precursor to Nb<SUB>2</SUB>O<SUB>5</SUB>, was spin-coated on to a platinum (Pt)-coated silicon substrate, and was then annealed at approximately 620 and 450 °C to form a Nb<SUB>2</SUB>O<SUB>5</SUB> film of polycrystalline and amorphous structure, respectively. A top electrode consisting of Ag, W, Au, or Pt was then coated onto the Nb<SUB>2</SUB>O<SUB>5</SUB> films to complete the fabrication. After a forming process of limited current compliance up to 10 mA, known as “electroforming”, a resistive switching phenomenon, independent of voltage polarity (unipolar switching), was observed at low operating voltages (0.59 ± 0.05 V<SUB>RESET</SUB> and 1.03 ± 0.06 V<SUB>SET</SUB>) with a high ON/OFF current ratio above 10<SUP>8</SUP>. The reported approach offers opportunities for preparing Nb<SUB>2</SUB>O<SUB>5</SUB>-based resistive switching memory devices from solution process.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2013/langd5.2013.29.issue-1/la303857b/production/images/medium/la-2012-03857b_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la303857b'>ACS Electronic Supporting Info</A></P>
Baek, Hyunhee,Lee, Chanwoo,Park, Jeongju,Kim, Younghoon,Koo, Bonkee,Shin, Hyunjung,Wang, Dayang,Cho, Jinhan The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.11
<P>Electrochemical properties of enzymes are of fundamental and practical importance in bio-electrochemical applications. These redox properties, which can cause the reversible changes in the current according to their redox reactions in solution, often depend on the chemical activity of transition metal ions as cofactors within the active sites of enzymes. Here, we demonstrate that the reversible resistance changes in enzyme-based multilayer films can be caused by the externally applied voltage as a result of charge trap/release of haem Fe<SUP>III</SUP>/Fe<SUP>II</SUP> redox couples in dry form. It is also demonstrated that the electrically bistable switching properties of redox enzymes can be applied to nonvolatile memory devices requiring low power consumption. For this study, cationic poly(allylamine hydrochloride) (PAH) was alternately layer-by-layer assembled with anionic catalase enzyme onto Pt-coated substrates until the desired number of layers was deposited. A top electrode was deposited onto (PAH/catalase)<SUB><I>n</I></SUB> multilayer films to complete device fabrication. When an external bias was applied to the devices, a switching phenomenon depending on the voltage polarity (<I>i.e.</I>, bipolar switching) was observed at low operating voltages (RESET at 1.8 V and SET voltage at −1.5 V), fast switching speed at the nanosecond level, and an ON/OFF current ratio of ∼10<SUP>2</SUP>. In the case of inserting insulating layers of about 2 nm thickness between adjacent catalase (CAT) layers, these devices exhibited the higher memory performance (ON/OFF current ratio of ∼10<SUP>6</SUP>) and the lower power consumption than those of (PAH/CAT)<SUB>15</SUB> multilayer devices.</P> <P>Graphic Abstract</P><P>We demonstrate that the redox enzymes can be used as electrically active materials for nonvolatile memory devices and that, furthermore their switching behavior originates from redox sites within enzymes. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm16231h'> </P>
Dong-Hoon Lee,Chanwoo Park,Cheol-Ha Baek,Chaeyeong Lee,Seung-Jae Lee,Hankyeol Song,Yong Hyun Chung Professional Technical Group on Nuclear Science 2017 IEEE transactions on nuclear science Vol.64 No.10
<P>Gamma-ray computed tomography (CT) has widely been used to inspect cracks, obstructions, and fluid flow in pipes. Previous studies have shown that the inspection accuracy is limited when materials in the pipe have a similar density. To overcome this drawback, we investigated a method to discriminate small density differences using a dual-energy gamma-ray CT. In this paper, the performance of a gamma-ray CT system was simulated using Geant4 Application for Tomographic Emission with three types of sources (Am-241, Co-57, and Cs-137). A polyvinyl chloride (PVC) pipe containing oil and sludge was modeled as a phantom. Sparsely acquired data were reconstructed using filtered back-projection and iterative total variation (TV) denoising algorithms. Each material discrimination procedure was performed with a postreconstruction technique. Our results clearly showed that the gamma-ray CT imaging with Am-241 and Co-57 sources and the TV denoising reconstruction algorithm can be used to inspect the internal structures based on discriminated images. The calculated areas of discriminated oil and sludge were within an error margin of 2% (oil: 78.4% and sludge: 21.6%) compared with the simulated phantom (oil: 80% and sludge: 20%). For both gamma sources, the calculated contrast-to-noise ratio (CNR) values with the TV denoising algorithm were the highest values for all structures (Am-241/Co-57: 18.03/28.95 for oil versus sludge, 41.67/31.53 for oil versus PVC pipe, and 23.64/31.53 for sludge versus PVC pipe). The feasibility of our approach and results indicates it usefulness for industrial fields that require structural inspections.</P>
Timing pickoff method for improvement of timing resolution in AGPET
Song Hankyeol,Park Chanwoo,Baek Min Kyu,Lee Seongyeon,Kim Kyu Bom,Chung Yong Hyun 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.2
Small-animal positron emission tomography (PET) systems are widely used for pathological and pharmacological studies. For good image quality, the timing resolution should be kept as low as possible, so we proposed a pulse reconstruction method based on curve ftting using a bi-exponential model for digital timing pickof. To evaluate the proposed method, fve diferent digital timing algorithms, leading edge discrimination (LED), digital constant fraction discrimination (DCFD), maximum rising interpolation (MRI), initial rising interpolation (IRI), and pulse reconstruction (PR) were established and compared. A single gamma pulse obtained from the silicon photomultiplier (SiPM) was simulated and the timing resolution was calculated according to the algorithms. Additionally, these methods were applied to the real PET dataset obtained from the AGPET detector and the timing resolution was derived. The simulation results proved that the PR method showed constant timing resolution independent from pulse rise time and sampling rate. In the experimental results, the PR method showed the best timing resolution of 0.9 ns to compare other digital methods. The results demonstrated that the proposed PR method can improve the performance of the small-animal PET with a relatively slow ADC.
Design and characterization of a hemispherical monitoring system for large-area radiation monitoring
Lee Seongyeon,Chung Yoon Soo,Park Chanwoo,Kang In Soo,Baek Min Kyu,Chung Yong Hyun 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.80 No.2
Radiation monitoring systems are needed in the rapidly growing radiation industrial fields. Many monitoring systems have been developed, but have limited ability to identify and locate radioactive materials over large areas. In this study, we designed and characterized a large-area monitoring system in the form of a hemispherical detector to cover a monitoring area with a 2π field of view with 324 spectrometers. GATE simulations and experimental validation were performed to evaluate and characterize the system’s performance. The 2D image of the source location was reconstructed. The results demonstrate the potential use of the proposed monitoring system in a given large area.
정형준(Hyeongjoon Jeong),곽진홍(Jinhong Gwak),노찬우(Chanwoo Noh),백인규(InGyu Baek),송윤석(YunSeok Song),이성진(Sungjin Lee) 한국통신학회 2022 한국통신학회 학술대회논문집 Vol.2022 No.2
자율주행 자동차는 기존 기계 자동차와는 달리 수많은 전자장치와 이를 구동시키는 소프트웨어들로 구성되기 때문에 다양한 요소기술들의 집약체라고 할 수 있다. 이런 자율주행 기술의 실현을 위해서는 여러 요소기술들을 종합적으로 분석하며 구현해봐야 하지만, 높은 비용구조와 안전성 이슈로 인해 현실적으로 어려움이 있다. 본 연구에서는 이런 어려움으로 스케일카를 통해 자율주행 자동차 구현에 대한 인사이트를 얻고자하였다. 특히 자동차 모터 스피드와 영상 인식 및 경로 판단 지연과의 상관성을 통해 트랙을 얼마나 안전하고 빠르게 완주할 수 있는지 알아보았다. 실험결과 엔비디아 젯슨 나노 기준으로 370 PWM (Pulse Wideth Modulation) 일 때 90° 곡선 경로를 안전하고 가장 빠르게 돌 수 있다는 것을 알 수 있었다. 또한 훈련 영상 파일 역시 해당 속도와 유사한 데이터들이 요구된다는 것을 알 수 있었다. 이런 연구 결과들을 통해 교내 자율주행차 경진대회의 15m*9m 트랙에서 22.7초 기록으로 1등의 결과를 얻을 수 있었다.