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High-Strength Chemical-Vapor–Deposited Graphene and Grain Boundaries
Lee, Gwan-Hyoung,Cooper, Ryan C.,An, Sung Joo,Lee, Sunwoo,van der Zande, Arend,Petrone, Nicholas,Hammerberg, Alexandra G.,Lee, Changgu,Crawford, Bryan,Oliver, Warren,Kysar, Jeffrey W.,Hone, James American Association for the Advancement of Scienc 2013 Science Vol.340 No.6136
<P><B>Graphene Staying Strong</B></P><P>Although exfoliated graphene can be extremely strong, it is produced on too small a scale for materials application. Graphene can be produced on a more practical scale by chemical vapor deposition, but the presence of grain boundaries between crystallites apparently weakens the material. <B>Lee <I>et al.</I></B> (p. 1073) show that postprocessing steps during the removal of the graphene sheets can oxidize the grain boundaries and weaken them. If these steps are avoided, the material is comparable in strength to exfoliated graphene.</P>
Direct observation of grain boundaries in chemical vapor deposited graphene
Lee, Jong-Young,Lee, Ji-Hwan,Kim, Min Jung,Dash, Jatis Kumar,Lee, Chul-Ho,Joshi, Rakesh,Lee, Sunwoo,Hone, James,Soon, Aloysius,Lee, Gwan-Hyoung Elsevier 2017 Carbon Vol.115 No.-
<P>Graphene has received great attention owing to its superior physical properties, making graphene suitable for multiple applications. Numerous graphene growth techniques have been developed in the past decade to provide scalable high quality graphene. Among these techniques, chemical vapor deposition (CVD) on catalytic metal films holds great promises for a large-scale graphene growth. Even though extensive efforts have been devoted to synthesize high quality graphene, formation of defects. In particular, grain boundaries (GBs) have a dominant effect on properties, motivating extensive efforts to tune the CVD growth process to minimize GB. Rapid imaging of GBs will significantly aid in studies of CVD graphene grain structure. Here we report a straightforward technique to optically observe GBs in CVD-grown graphene via optical microscopy, allowing rapid assessment of graphene quality as well as the number of layers. The local oxidation of copper through the damaged GBs induces an optically discernable color change in the underlying copper due to different extend of oxidation between the two copper regions under grains and GBs. Our observation technique for GBs of graphene paves a path for understanding fundamental mechanisms of graphene growth and efficient quality evaluation of large-scale graphene sheet for mass production. (C) 2017 Elsevier Ltd. All rights reserved.</P>
Hyoung-ho Mo,Jinsol Hong,Gwan-Seok Lee,Jung-Joon Park,Doo-Hyung Lee,Kijong Cho 한국응용곤충학회 2015 한국응용곤충학회 학술대회논문집 Vol.2015 No.04
Thc climate change has the potential to significantly modify the actual distribution of insect pest with unknown consequences on agricultural systems and management strategies. In this study, Thrips palmi Karny was selected to predict distribution under climate change. T. palmi was introduced and first recorded in 1993 in Korea, and has become a serious pest of vegetable and ornamental crops. The MaxEnt was applied to T. palmi to predict its potential geographic distribution in Korea and Japan under the RCP 8.5 climate changing scenario. The MaxEnt software package is one of the most popular tools for species distribution and environmental niche modeling. The habitat prediction model of T. palmi in Korea was validated by the distribution of T. palmi in Japan. Based on the MaxEnt modeling, T. palmi would expand their potential distribution to whole Korean peninsula except the alpine region in Gangwon-do and Yanggang-do and Hamgyeongbuk-do in 2070s. Therefore, the monitoring system and management strategy for T. palmi should be reconsidered and re-evaluated.
Lee, Gwan-Hyoung,Yu, Young-Jun,Cui, Xu,Petrone, Nicholas,Lee, Chul-Ho,Choi, Min Sup,Lee, Dae-Yeong,Lee, Changgu,Yoo, Won Jong,Watanabe, Kenji,Taniguchi, Takashi,Nuckolls, Colin,Kim, Philip,Hone, James American Chemical Society 2013 ACS NANO Vol.7 No.9
<P>Atomically thin forms of layered materials, such as conducting graphene, insulating hexagonal boron nitride (hBN), and semiconducting molybdenum disulfide (MoS<SUB>2</SUB>), have generated great interests recently due to the possibility of combining diverse atomic layers by mechanical “stacking” to create novel materials and devices. In this work, we demonstrate field-effect transistors (FETs) with MoS<SUB>2</SUB> channels, hBN dielectric, and graphene gate electrodes. These devices show field-effect mobilities of up to 45 cm<SUP>2</SUP>/Vs and operating gate voltage below 10 V, with greatly reduced hysteresis. Taking advantage of the mechanical strength and flexibility of these materials, we demonstrate integration onto a polymer substrate to create flexible and transparent FETs that show unchanged performance up to 1.5% strain. These heterostructure devices consisting of ultrathin two-dimensional (2D) materials open up a new route toward high-performance flexible and transparent electronics.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-9/nn402954e/production/images/medium/nn-2013-02954e_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn402954e'>ACS Electronic Supporting Info</A></P>
Luminescence of $Eu^{3+}$ and $Sm^{3+}$ Doped Potassium Tungstate Phosphor
Lee, Gwan-Hyoung,Kim, Tae-Hyung,Kang, Shin-Hoo The Korean Infomation Display Society 2005 Journal of information display Vol.6 No.2
The luminescent properties of $Eu^{3+}$ and $Sm^{3+}$ doped potassium tungstate phosphor are investigated. The $K_{4-3x}(WO_4)_2:Eu^{3+}\;_x,Sm^{3+}\;_y$ phosphor is produced by firing the mixed precursors, followed by re-firing with a flux. The re-firing process results in the defect-free surface and uniform growth of the particles. The strong absorption in the region of ultra violet light is observed due to the 4f-4f electron transitions of the $Eu^{3+}$ and $Sm^{3+}$ ions. The doping concentration of europium into potassium tungstate is relatively high, compared to other host materials. It is revealed that the crystal structure is a monoclinic with space group, C2/c. This crystal structure facilitated the $Eu^{3+}$ ions to be located with the Eu-Eu distance larger than 5 ${\AA}$ so that concentration quenching does not occur even at high doping concentration. The excitation spectrum could be adjusted by the introduction of the samarium. A small amount of the $Sm^{3+}$ ions that acts as a sensitizer increases the energy absorption peak around 405 nm.
Mok, Young Geun,Lee, Byoung Doo,Kim, Young Jin,Lee, Chang Eun,Kim, Dong Gwan,Lee, Joohyun,Shim, Jaekyung,Meng, Yuling,Rosen, Barry P.,Choi, Jong Soon,Shin, Hyoung Sun,Kim, Seong-Ki,Lee, June Seung,Hwa Elsevier 2008 FEBS letters Vol.582 No.6
<P><B>Abstract</B></P> <P>We cloned a plant gene, <I>Ntcyc07</I>, conferring arsenite tolerance by expressing a tobacco expression library in WT yeast (Y800). Expression of <I>Ntcyc07</I> increased the tolerance to As(III) and decreased its accumulation, suggesting that the enhanced As(III) tolerance resulted from a reduction of the intracellular arsenic level. Interestingly, expression of <I>Ntcyc07</I> increased the expression of the As(III) export carrier <I>ACR3</I>, but repressed that of As(III) uptake channel <I>FPS1</I>. Ntcyc07p interacted with Acr1p, which is the transcriptional activator of <I>ACR3</I>, but not with the <I>ACR3</I> promoter. Taken together, the data indicated that Ntcyc07p promoted As(III) tolerance by decreasing the intracellular level of As(III) via increasing the expression of <I>ACR3</I> and reducing that of <I>FPS1.</I> </P>
Effect of surface morphology on friction of graphene on various substrates.
Cho, Dae-Hyun,Wang, Lei,Kim, Jin-Seon,Lee, Gwan-Hyoung,Kim, Eok Su,Lee, Sunhee,Lee, Sang Yoon,Hone, James,Lee, Changgu RSC Pub 2013 Nanoscale Vol.5 No.7
<P>The friction of graphene on various substrates, such as SiO2, h-BN, bulk-like graphene, and mica, was investigated to characterize the adhesion level between graphene and the underlying surface. The friction of graphene on SiO2 decreased with increasing thickness and converged around the penta-layers due to incomplete contact between the two surfaces. However, the friction of graphene on an atomically flat substrate, such as h-BN or bulk-like graphene, was low and comparable to that of bulk-like graphene. In contrast, the friction of graphene folded onto bulk-like graphene was indistinguishable from that of mono-layer graphene on SiO2 despite the ultra-smoothness of bulk-like graphene. The characterization of the graphene's roughness before and after folding showed that the corrugation of graphene induced by SiO2 morphology was preserved even after it was folded onto an atomically flat substrate. In addition, graphene deposited on mica, when folded, preserved the same corrugation level as before the folding event. Our friction measurements revealed that graphene, once exfoliated from the bulk crystal, tends to maintain its corrugation level even after it is folded onto an atomically flat substrate and that ultra-flatness in both graphene and the substrate is required to achieve the intimate contact necessary for strong adhesion.</P>
Atomically thin p–n junctions with van der Waals heterointerfaces
Lee, Chul-Ho,Lee, Gwan-Hyoung,van der Zande, Arend M.,Chen, Wenchao,Li, Yilei,Han, Minyong,Cui, Xu,Arefe, Ghidewon,Nuckolls, Colin,Heinz, Tony F.,Guo, Jing,Hone, James,Kim, Philip Nature Publishing Group, a division of Macmillan P 2014 Nature nanotechnology Vol.9 No.9
Semiconductor p–n junctions are essential building blocks for electronic and optoelectronic devices. In conventional p–n junctions, regions depleted of free charge carriers form on either side of the junction, generating built-in potentials associated with uncompensated dopant atoms. Carrier transport across the junction occurs by diffusion and drift processes influenced by the spatial extent of this depletion region. With the advent of atomically thin van der Waals materials and their heterostructures, it is now possible to realize a p–n junction at the ultimate thickness limit. Van der Waals junctions composed of p- and n-type semiconductors—each just one unit cell thick—are predicted to exhibit completely different charge transport characteristics than bulk heterojunctions. Here, we report the characterization of the electronic and optoelectronic properties of atomically thin p–n heterojunctions fabricated using van der Waals assembly of transition-metal dichalcogenides. We observe gate-tunable diode-like current rectification and a photovoltaic response across the p–n interface. We find that the tunnelling-assisted interlayer recombination of the majority carriers is responsible for the tunability of the electronic and optoelectronic processes. Sandwiching an atomic p–n junction between graphene layers enhances the collection of the photoexcited carriers. The atomically scaled van der Waals p–n heterostructures presented here constitute the ultimate functional unit for nanoscale electronic and optoelectronic devices.
문형관 ( Hyoung-gwan-moon ),이덕규 ( Deok-gyu-lee ) 한국정보처리학회 2022 한국정보처리학회 학술대회논문집 Vol.29 No.1
라즈베리파이를 통하여 차량 내부의 모든 정보를 입력받아 영상처리 등을 이용하여 차량 내부를 감시 및 탐색, 위험요소 발생 시 이를 사용자에게 전달하고 직접적으로 차량 내 부저 등으로 소리를 내어서 주변 사람들에게 알려 문제를 해결하고자 한다.