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Coulomb Interaction Induced Gap in an Al/SiO<sub>2</sub>/Si:P tunnelling Device
Jo, Yongcheol,Kim, Jongmin,Cho, Sangeun,Kim, Hyungsang,Im, Hyunsik The Korean Vacuum Society 2017 Applied Science and Convergence Technology Vol.26 No.3
Strongly correlated electron systems which induce strong electron-electron interaction at ultra-low temperatures have always been an intriguing topic in mesoscopic condensed matter physics. Below 130 mK, a peculiar gap can be found in Al/$SiO_2$/Si:P structured tunnelling devices. The gap survives at the base temperature of more than 1800 gauss (30 mK), contrary to the superconductivity of the top Al electrode, which is completely suppressed above 100 gauss. This outcome implies that the observed gap is induced by Coulomb interaction in the heavily doped Si.
Tailoring resistive switching characteristics in WOx films using different metal electrodes
Jo, Yongcheol,Kim, Jongmin,Woo, Hyeonseok,Kim, Duwhan,Lee, James W.,Inamdar, Akbar I.,Im, Hyunsik,Kim, Hyungsang Elsevier 2014 CURRENT APPLIED PHYSICS Vol.14 No.1
We have investigated the role of the metal/oxide junction interface on the resistive switching (RS) characteristics in WO3+x films. The WOx films are fabricated on Pt substrates by magnetron sputtering at room temperature. Top metal contact (Au or Al) is fabricated by using thermal evaporator. The thicknesses of WOx films and top electrodes are 1 mu m and 200 nm, respectively. It has been found that the bi-polar RS direction is dependent on the choice of top metal electrode, Au or Al. The sample with a Au top electrode shows clockwise (CW) RS mode whilst the sample with a Al top electrode shows counter-clockwise (CCW) RS mode. The on/off ratio is 10 times for Au/WOx/Pt and 100 times for Al/WOx/Pt. The bi-polar RS modes are modeled in terms of the difference in the electronegativity of the top and bottom electrodes. (C) 2013 Elsevier B.V. All rights reserved.
국내 재배 베리류의 화학 조성 및 기능성 성분과 항산화 활성
이용철(Yongcheol Lee),이집호(Jib-Ho Lee),김성단(Sung-Dan Kim),장민수(Min-Su Chang),조인순(In-Soon Jo),김시정(Si-Jeong Kim),황금택(Keum Taek Hwang),조한빈(Han-Bin Jo),김정헌(Jung-Hun Kim) 한국식품영양과학회 2015 한국식품영양과학회지 Vol.44 No.9
국내에서 주로 재배되는 대표적인 베리류에 대한 화학 조성 및 기능성을 알아보고자 일정 시기에 수확한 오디, 블랙라즈베리, 라즈베리, 블루베리의 pH, 산도, 유리당, γ-aminobutyric acid(GABA), 무기질 함량, phenolic compound, 항산화 활성을 조사하여 비교하였다. 베리류 4종의 pH는 3.3~5.2로 블루베리가 가장 낮았고 오디가 가장 높은 반면, 산도는 0.26~1.10%(w/w)로 오디가 가장 낮았고 블랙라즈베리가 가장 높았다. 베리류에서 검출된 유리당인 fructose와 glucose는 같은 비율로 존재하였고, 그 총량은 4.80~12.93%(w/w)로 오디가 가장 높았으며 블랙라즈베리가 가장 낮았다. GABA는 오디에 69.3 mg/100 g이 함유되어 있었는데, 이는 다른 베리류에 비해 3배 이상 많은 양이다. 베리류에 함유된 주요 무기질은 칼륨, 칼슘, 마그네슘이었고, 총 무기질 함량은 92.9~256.0 mg/100 g으로 블랙라즈베리에 유의적으로 높게 함유되어 있었으며(P<0.05) 블루베리가 가장 낮았다. Total polyphenol과 total flavonoid 함량은 각각 198.2~547.2 mg/100 g과 5.0~94.6 mg/100g의 범위로 블랙라즈베리가 가장 높았고, 라즈베리는 유의적으로 가장 낮았다(P<0.05). Total anthocyanin은 19.8~385.6 mg/100 g의 범위로 블랙라즈베리가 가장 높았고, 라즈베리가 유의적으로 낮았다(P<0.05). Total PA(phenolic acids)는 블랙라즈베리와 라즈베리에 각각 14.0 mg/kg과 5.9 mg/kg이 함유되어 있었는데 이는 오디에 함유된 50.4 mg/kg보다 낮았으며, 391.4 mg/kg으로 가장 높게 함유된 블루베리에는 PA의 대부분이 chlorogenic acid였다. 베리류 4종의 항산화 활성을 DPPH 및 ABTS free radical scavenging activity를 분석하여 Trolox equivalent 값으로 나타낸 결과 Trolox equivalent antioxidant capacity와 total polyphenol, total anthocyanin, total flavonoid 함량과는 유의적인 양(+)의 상관관계(Pearson 상관계수 r≥0.85; P<0.01)를 나타내었고, 블랙라즈베리가 DPPH 및 ABTS 항산화 활성이 가장 우수하였다. Berry fruits are rich in phytochemicals, including polyphenols, anthocyanins, phenolic acids, and organic acids, which are known to have beneficial effects on health. The aim of this study was to investigate chemical composition, functional constituents, and antioxidant activities of mulberry, black raspberry, raspberry, and blueberry cultivated in Korea. Acidity of the four berries ranged from 0.26% to 1.10%, and pH ranged from 3.3 to 5.2. Total mineral contents of the four berries ranged from 92.9 to 256.0 mg/100 g. Among the berries, mulberry contained the most abundant total free sugars, and glucose and fructose were the major sugars in the berries. Mulberry contained more than three times as much γ-aminobutyric acid as the content of the other berries. Blueberry contained more free phenolic acid than the other berries. Especially, chlorogenic acids were the major free phenolic acids in blueberry. Black raspberry had the highest amount of polyphenols, anthocyanins, and flavonoids among the berries and showed the highest antioxidant activity.
Enhanced Photosensitivity in Monolayer MoS<sub>2</sub> with PbS Quantum Dots
Cho, Sangeun,Jo, Yongcheol,Woo, Hyeonseok,Kim, Jongmin,Kwak, Jungwon,Kim, Hyungsang,Im, Hyunsik The Korean Vacuum Society 2017 Applied Science and Convergence Technology Vol.26 No.3
Photocurrent enhancement has been investigated in monolayer (1L) $MoS_2$ with PbS quantum dots (QDs). A metal-semiconductor-metal (Au-1L $MoS_2$-Au) junction device is fabricated using a standard photolithography method. Considerably improved photo-electrical properties are obtained by coating PbS QDs on the Au-1L $MoS_2$-Au device. Time dependent photoconductivity and current-voltage characteristics are investigated. For the QDs-coated $MoS_2$ device, it is observed that the photocurrent is considerably enhanced and the decay life time becomes longer. We propose that carriers in QDs are excited and transferred to the $MoS_2$ channel under light illumination, improving the photocurrent of the 1L $MoS_2$ channel. Our experimental findings suggest that two-dimensional layered semiconductor materials combined with QDs could be used as building blocks for highly-sensitive optoelectronic detectors including radiation sensors.
Effect of heating on electrical transport in AlGaN/GaN Schottky barrier diodes on Si substrate
Woo, Hyeonseok,Jo, Yongcheol,Kim, Jongmin,Roh, Cheonghyun,Lee, Junho,Kim, H.,Im, H.,Hahn, Cheol-koo,Park, Jungho Elsevier 2014 CURRENT APPLIED PHYSICS Vol.14 No.1
Thermal properties of the AlGaN/GaN Schottky barrier diodes were investigated, using a pulsed-IV measurement technique. The thermally degraded mobility in the DC-bias configuration was restored, when the pulse-bias voltages were applied. It was observed that heat generation was minimized, using a pulse width of 500 ns and pulse period of 10 ms. For the SBDs consisting of 5 mu m of anode-cathode distance, on-resistance measured by the pulse-IV and DC-IV were 1.6 and 6.2 Omega-mm, respectively. We also demonstrated the device-width dependence of the thermal properties of the SBDs. We found that the performance of the power devices can be greatly influenced by the heat generation. (C) 2013 Elsevier B.V. All rights reserved.