Morphology Control of Zinc Oxide Nanostructure on Single Layer Graphene

Ahn, Seungbae,Vijayarangamuthu, K.,Jeon, Ki-Joon American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.5

<P>Various morphologies of zinc oxide (ZnO) nanostructures on single layer graphene were synthesized by electrodeposition method. The current density was utilized to control the morphology of the ZnO. The Scanning Electron Microscope (SEM) was used to examine the surface morphology of the samples. SEM analysis shows morphology changes to nanorod, flower, and flakes with increase in the current density from 0.1, 0.2, and 0.3 mA/cm(-1) respectively. The XRD, XPS, and Raman spectroscopy were adopted to characterize the ZnO nanostructure and to understand the formation of various morphologies. The Raman result clearly shows extra modes due to for flakes structure caused by c-axis orientation along the substrate direction. Further, XPS data also supports formation of ZnO without any other intermediate compound such as Zn(OH)(2). The formation of various morphologies was correlated to the formation different ratio of Zn2+ and OH- ions and the change in growth direction due to various current densities.</P>

불포화 특성을 고려한 투수성 포장 시스템의 침투성 수치해석

Seungbae Kim,Jaehun Ahn,Bertrand Teodosio,Hyunjun Shin 한국재난정보학회 2015 한국재난정보학회 논문집 Vol.11 No.3

효과적인 도심 홍수 감소 및 물순환 기법 중 하나로 투수성 포장의 적용을 들 수 있다. 도심 물순환 및 방재를 위한 수단으로 투수성 포장의 적용은 국제적으로 점차 확대되고 있는 실정이다. 투수성 포장 내의 침투는 대부분의 경우 불포화 상태에서 시작하나, 현재 투수성 포장재의 흙-수분특성곡선의 산정 및 이를 바탕으로 한 투수성 포장 시스템의 침투성에 대한 연구는 거의 찾아볼 수 없다. 본 연구에서는, 먼저 실내시험을 통해 투수성 포장재의 포화투수계수와 흙-수분특성곡선을 산정하고, 이를 바탕으로 유한요소해석을 통해 강우시 특정 투수성 포장 시스템의 침투특성 및 홍수 저감 효과를 분석하는 것을 그 목적으로 한다. 실험에 사용된 현장 투수성 콘크리트 시료의 흙-수분특성곡선은, 모관흡입력이 증가함에 따라 공기 유입 후 체적함수비가 상대적으로 급격하게 감소하였다. 유한요소해석 결과로부터, 불투수성 포장과 비교하였을 때, 즉 강우가 침투 없이 바로 유출이 되는 경우와 비교하여, 투수성 포장 시스템의 노반으로 침투가 불가능한 경우에도, 투수성 포장 시스템이 강우의 지표유출을 효과적으로 지체 및 감소시키는 것을 확인하였다. Effective urban flood reduction and restoration of natural water cycle at present include the application of permeable pavements. The application of permeable pavement addresses urban water cycle and disaster related events which gained attention internationally. However, few researches have been conducted to investigate unsaturated behavior and evaluate the water characteristics curves of these type of pavement materials most especially in the unsaturated state. In this study, first the saturated permeability and the soil-water characteristics curve of a pervious concrete are evaluated based on laboratory tests, and, based on experimental results, the infiltration of permeable pavement system is numerically modelled. In the soil-water characteristics curve of a pervious concrete, the volumetric water content drops very steeply after the air entry value with increasing matric suction. From the finite element analyses, the performance of the permeable pavement when compared to impermeable pavement, confirmed that the whole system effectively delayed and reduced runoff.

불포화 특성을 고려한 투수성 포장 시스템의 침투성 수치해석

Kim, Seungbae,Ahn, Jaehun,Teodosio, Bertrand,Shin, Hyunjun 한국재난정보학회 2015 한국재난정보학회 논문집 Vol.11 No.3

Effective urban flood reduction and restoration of natural water cycle at present include the application of permeable pavements. The application of permeable pavement addresses urban water cycle and disaster related events which gained attention internationally. However, few researches have been conducted to investigate unsaturated behavior and evaluate the water characteristics curves of these type of pavement materials most especially in the unsaturated state. In this study, first the saturated permeability and the soil-water characteristics curve of a pervious concrete are evaluated based on laboratory tests, and, based on experimental results, the infiltration of permeable pavement system is numerically modelled. In the soil-water characteristics curve of a pervious concrete, the volumetric water content drops very steeply after the air entry value with increasing matric suction. From the finite element analyses, the performance of the permeable pavement when compared to impermeable pavement, confirmed that the whole system effectively delayed and reduced runoff. 효과적인 도심 홍수 감소 및 물순환 기법 중 하나로 투수성 포장의 적용을 들 수 있다. 도심 물순환 및 방재를 위한 수단으로 투수성 포장의 적용은 국제적으로 점차 확대되고 있는 실정이다. 투수성 포장 내의 침투는 대부분의 경우 불포화 상태에서 시작하나, 현재 투수성 포장재의 흙-수분특성 곡선의 산정 및 이를 바탕으로 한 투수성 포장 시스템의 침투성에 대한 연구는 거의 찾아볼 수 없다. 본 연구에서는, 먼저 실내시험을 통해 투수성 포장재의 포화투수계수와 흙-수분특성곡선을 산정하고, 이를 바탕으로 유한요소해석을 통해 강우시 특정 투수성 포장 시스템의 침투특성 및 홍수 저감 효과를 분석하는 것을 그 목적으로 한다. 실험에 사용된 현장 투수성 콘크리트 시료의 흙-수분특성곡선은, 모관흡입력이 증가함에 따라 공기 유입 후 체적함수비가 상대적으로 급격하게 감소하였다. 유한요소해석 결과로부터, 불투수성 포장과 비교하였을 때, 즉 강우가 침투 없이 바로 유출이 되는 경우와 비교하여, 투수성 포장 시스템의 노반으로 침투가 불가능한 경우에도, 투수성 포장 시스템이 강우의 지표유출을 효과적으로 지체 및 감소시키는 것을 확인하였다.

Single Layer Graphene-NiO Composite for Cholesterol Biosensor

Arunkumar RENGARAJ,Yuvaraj HALDORAI,Seungbae AHN,Ki-Joon JEON,Young-Kyu HAN,Yun Suk HUH 한국생물공학회 2014 한국생물공학회 학술대회 Vol.2014 No.10

공동현상을 고려한 펌프 인듀서 설계

정근화(Keun-Hwa Jung),안광운(Kwang-Woon Ahn),이승배(Seungbae Lee),김진화(Jin-Hwa Kim),강신형(Shin-Hyoung Kang) 한국유체기계학회 2001 유체기계 연구개발 발표회 논문집 Vol.- No.-

The cavitation causes suction performance and efficiency of the high-speed pump to be reduced significantly. To diminish these effects, the inducer has been used Most of the inducer is designed at a maximum efficiency point of the pump, therefore suction performance drop due to effects of flow separation and inlet inverse flow is often observed at off-design point. The objective of this study is to find out the cavitation modes at various conditions by applying event detection technique and to design an inducer reducing cavitation. The pressure fluctuations at each cavitating condition were measured at inducer inlet and outlet locations using pressure transducers, which were located 90 degrees apart from each other to identify the cavitation modes. The time-frequency characteristics were analyzed by using Choi-williams distribution. In the second part of this paper, the inducer design method which uses nominal performance characteristic and onset condition of cavitation is introduced and applied to real situation.

Photochemical Hydrogen Doping Induced Embedded Two-Dimensional Metallic Channel Formation in InGaZnO at Room Temperature

Kim, Myeong-Ho,Lee, Young-Ahn,Kim, Jinseo,Park, Jucheol,Ahn, Seungbae,Jeon, Ki-Joon,Kim, Jeong Won,Choi, Duck-Kyun,Seo, Hyungtak American Chemical Society 2015 ACS NANO Vol.9 No.10

<P>The photochemical tunability of the charge-transport mechanism in metal-oxide semiconductors is of great interest since it may offer a facile but effective semiconductor-to-metal transition, which results from photochemically modified electronic structures for various oxide-based device applications. This might provide a feasible hydrogen (H)-radical doping to realize the effectively H-doped metal oxides, which has not been achieved by thermal and ion-implantation technique in a reliable and controllable way. In this study, we report a photochemical conversion of InGaZnO (IGZO) semiconductor to a transparent conductor via hydrogen doping to the local nanocrystallites formed at the IGZO/glass interface at room temperature. In contrast to thermal or ionic hydrogen doping, ultraviolet exposure of the IGZO surface promotes a photochemical reaction with H radical incorporation to surface metal–OH layer formation and bulk H-doping which acts as a tunable and stable highly doped n-type doping channel and turns IGZO to a transparent conductor. This results in the total conversion of carrier conduction property to the level of metallic conduction with sheet resistance of ∼16 Ω/□, room temperature Hall mobility of 11.8 cm<SUP>2</SUP> V<SUP>–1</SUP> sec<SUP>–1</SUP>, the carrier concentration at ∼10<SUP>20</SUP> cm<SUP>–3</SUP> without any loss of optical transparency. We demonstrated successful applications of photochemically highly n-doped metal oxide via optical dose control to transparent conductor with excellent chemical and optical doping stability.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-10/acsnano.5b05342/production/images/medium/nn-2015-053422_0007.eps'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5b05342'>ACS Electronic Supporting Info</A></P>

Electrodeposition of flower-like nickel oxide on CVD-grown graphene to develop an electrochemical non-enzymatic biosensor

Rengaraj, Arunkumar,Haldorai, Yuvaraj,Kwak, Cheol Hwan,Ahn, Seungbae,Jeon, Ki-Joon,Park, Seok Hoon,Han, Young-Kyu,Huh, Yun Suk The Royal Society of Chemistry 2015 Journal of Materials Chemistry B Vol.3 No.30

<P>We demonstrated a non-enzymatic cholesterol sensor based on a nickel oxide (NiO) and high quality graphene composite for the first time. Graphene was grown by a chemical vapor deposition technique (CVD). The nanocomposite was fabricated through the electrodeposition of nickel hydroxide onto the surface of the CVD-grown graphene, which was followed by thermal annealing. The successful formation of the NiO/graphene composite was confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The deposition of flower-like NiO onto the graphene surface was confirmed by scanning electron microscopy. Electrochemical analyses were conducted to investigate the characteristics of the sensor during the detection of cholesterol. The sensor showed a high sensitivity of 40.6 mA μM<SUP>−1</SUP> cm<SUP>−2</SUP>, a rapid response time of 5 s, and a low detection of limit of 0.13 μM. We also investigated the effects of common interfering substances on the ability of the sensor to detect cholesterol. Furthermore, we successfully determined the cholesterol in a milk sample using the developed sensor. The composite electrode exhibited excellent detection of cholesterol with good reproducibility and long-term stability owing to the combined effects of NiO and graphene.</P>

Fabrication of enzyme-free electrochemical cholesterol sensor based on NiO/single-layer graphene composite

Arunkumar RENGARAJ,Yuvaraj HALDORAI,Cheol Hwan KWAK,Seungbae AHN,Ki-joon JEON,Yong-Kyu HAN,Yun Suk HUH 한국생물공학회 2015 한국생물공학회 학술대회 Vol.2015 No.4

Complementary Schottky diode formation with carbon buffer and <i>p-</i>doped single layer graphene on intrinsic SiC <i>via</i> fluorine intercalation

Lee, Sang Yeon,Kim, Jinseo,Ahn, Seungbae,Jeon, Ki-Joon,Seo, Hyungtak Elsevier 2019 Carbon Vol.142 No.-

<P><B>Abstract</B></P> <P>A practical application of graphene is in transistors and diodes fabricated through processes compatible with integrated circuit fabrication processes that are currently used. In this paper, a highly controlled gas phase fluorination treatment (using XeF<SUB>2</SUB>) of an intrinsic Si-terminated SiC (i-SiC) substrate and a (6√3ⅹ6√3)R30° carbon buffer layer is shown to effectively convert the buffer layer to <I>p-</I>doped SLG (<I>p-</I>SLG), which is decoupled from the i-SiC substrate through F intercalation. The electrical properties of two diode structures, (1) metal/SiC with buffer layer and (2) <I>p-</I>SLG/SiC, were investigated considering the bias-dependent carrier injection at each interface. The analysis results suggest that the diode turn-on for each diode is due to carrier injection from the metal or <I>p-</I>SLG to the i-SiC substrate, with an exponential modulation of the thermionic injection driven by the image barrier lowering effect. A complementary SLG-based SiC diode formation scheme is demonstrated, as hole injection from <I>p-</I>SLG is the origin of positive bias diode turn-on in the second diode type, whereas the diode having metal/SiC with buffer structure showed negative bias turn-on.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>