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순수한 물 용매에서 Langmuir-Blodgett 법으로 제조한 이황화몰리브덴 박막의 전기적 특성 관찰
조대현(Dae-Hyun Cho),이승기(Seoung-Ki Lee),이창구(Changgu Lee) 대한전기학회 2019 전기학회논문지 Vol.68 No.2
In this study, nanometer-thick molybdenum disulfide (MoS₂) films were fabricated by Langmuir-Blodgett method and morphological characteristics and electrical properties were observed. The thickness of the thin films measured by AFM was about 10 nm, and the sheets constituting the thin films had a width of 100-400 nm in the plane direction. This means that micrometer-level molybdenum disulfide powder is dispersed in pure water through ultrasonic waves and self-assembled in the form of a thin film from nano-sheets by the Langmuir-Blodgett method. Raman spectra of the thin films showed that the nanometer-thick molybdenum disulfide films were obtained without the chemical change of the molybdenum disulfide. We conclude that the MoS₂ films fabricated by Langmuir-Blodgett method have semiconducting property from the measurement of 2.5 times amplified current than dark state (at 0.5 V). Furthermore, we analyze the electrical properties of MoS₂ film by measuring channel current depend on gate voltage. From the conventional I-V characteristic, we confirm that the MoS₂ film has n-type semiconducting characteristic.
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>
Self-Assembly of Silver Nanowire Ring Structures Driven by the Compressive Force of a Liquid Droplet
Seong, Baekhoon,Park, Hyun Sung,Chae, Ilkyeong,Lee, Hyungdong,Wang, Xiaofeng,Jang, Hyung-Seok,Jung, Jaehyuck,Lee, Changgu,Lin, Liwei,Byun, Doyoung American Chemical Society 2017 Langmuir Vol.33 No.14
<P>In a nanowire dispersed in liquid droplets, the interplay between the surface tension of the liquid and the elasticity of the nanowire determines the final morphology of the bent or buckled nanowire. Here, we investigate the fabrication of a silver nanowire ring generated as the nanowire encapsulated inside of fine droplets. We used a hybrid aerodynamic and electrostatic atomization method to ensure the generation of droplets with scalable size in the necessary regime for ring formation. We analytically calculate the compressive force of the droplet driven by surface tension as the key mechanism for the self-assembly of ring structures. Thus, for potential large-scale manufacturing, the droplet size provides a convenient parameter to control the realization of ring structures from nanowires.</P>
Sridhar, Vadahanambi,Kim, Hyun-Jun,Jung, Jung-Hwan,Lee, Changgu,Park, Sungjin,Oh, Il-Kwon American Chemical Society 2012 ACS NANO Vol.6 No.12
<P>The development of three-dimensional carbon-based nanostructures is the next step forward for boosting industrial applications of carbon nanomaterials such as graphenes and carbon nanotubes. Some defects, which have been considered as detrimental factors for maintaining exceptional materials properties of two-dimensional graphene, can be actively used to synthesize three-dimensional graphene-based carbon nanostructures. Here we describe a fast and heretofore unreported defect-engineered method to synthesize three-dimensional carbon nanohybrid structures with strong bonding between graphene nanoplatelets and carbon nanotubes using simple microwave irradiation and an ionic liquid. Our one-pot method utilizes defect-engineered sequential processes: microwave-based defect generation on graphene nanoplatelets, anchoring of palladium nanoparticles on these defects, and subsequent growth of carbon nanotubes by use of an ionic liquid. The unique three-dimensional nanostructures showed an ultrahigh redox capacitance due to high porosity, a high surface-to-volume ratio from the spacer role of vertically standing one-dimensional carbon nanotubes on graphene sheets, and capacitance-like redox response of the palladium nanoparticles. The proposed defect-engineered method could lead to novel routes to synthesizing three-dimensional graphene-based nanostructures with exceptionally high performance in energy storage systems.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2012/ancac3.2012.6.issue-12/nn3046133/production/images/medium/nn-2012-046133_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn3046133'>ACS Electronic Supporting Info</A></P>
Designed Three-Dimensional Freestanding Single-Crystal Carbon Architectures
Park, Ji-Hoon,Cho, Dae-Hyun,Moon, Youngkwon,Shin, Ha-Chul,Ahn, Sung-Joon,Kwak, Sang Kyu,Shin, Hyeon-Jin,Lee, Changgu,Ahn, Joung Real American Chemical Society 2014 ACS NANO Vol.8 No.11
<P>Single-crystal carbon nanomaterials have led to great advances in nanotechnology. The first single-crystal carbon nanomaterial, fullerene, was fabricated in a zero-dimensional form. One-dimensional carbon nanotubes and two-dimensional graphene have since followed and continue to provide further impetus to this field. In this study, we fabricated designed three-dimensional (3D) single-crystal carbon architectures by using silicon carbide templates. For this method, a designed 3D SiC structure was transformed into a 3D freestanding single-crystal carbon structure that retained the original SiC structure by performing a simple single-step thermal process. The SiC structure inside the 3D carbon structure is self-etched, which results in a 3D freestanding carbon structure. The 3D carbon structure is a single crystal with the same hexagonal close-packed structure as graphene. The size of the carbon structures can be controlled from the nanoscale to the microscale, and arrays of these structures can be scaled up to the wafer scale. The 3D freestanding carbon structures were found to be mechanically stable even after repeated loading. The relationship between the reversible mechanical deformation of a carbon structure and its electrical conductance was also investigated. Our method of fabricating designed 3D freestanding single-crystal graphene architectures opens up prospects in the field of single-crystal carbon nanomaterials and paves the way for the development of 3D single-crystal carbon devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-11/nn504956h/production/images/medium/nn-2014-04956h_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn504956h'>ACS Electronic Supporting Info</A></P>
김광섭(Kwang-Seop Kim),이희정(Hee-Jung Lee),이창구(Changgu Lee),이승기(Seoung-Ki Lee),장호욱(Ho-Uk Jang),안종현(Jong-Hyun Ahn),김재현(Jae-Hyun Kim),이학주(Hak-Joo Lee) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.4
본 연구에서는 CVD 방법으로 성장된 그래핀의 마찰 특성을 알아보기 위해 마이크로트라이보미터를 이용하여 마찰력을 측정하였으며, SiO₂ 표면에서 측정된 마찰력과 비교하였다. 실험 결과, SiO₂ 기판 위에 코팅된 그래핀은 마찰 저감 효과가 매우 뛰어난 것으로 확인되었다. CVD 방법으로 성장된 그래핀을 MEMS와 NEMS에 적용하여 윤활막으로 사용할 경우 접촉면 사이의 마찰력을 효과적으로 감소시킬 수 있을 거라 예상된다. Surface forces, such as adhesion and friction forces, are crucial in the fabrication and operation of microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) as well as in the nanofabrication processes such as nanoimprint lithography and transfer assembly process. Various lubricant materials, patterns, and surface treatment processes have been developed for control of the interfacial forces and lubrication between contacting surfaces. Graphite is a traditional good solid lubricant because of its lamella structure with low shearing resistance. Graphene may be one of good candidates for lubrication on the micro/nanoscale because graphene is atomically thin and strong, and is stacked in lamella structure similar to graphite. In this study, frictional properties of graphene synthesized by chemical vapor deposition (CVD) were investigated. The results show that the graphene is so effective to reduce friction.
Lee, Youngbin,Kim, Hyunmin,Lee, Jinhwan,Yu, Seong Hun,Hwang, Euyheon,Lee, Changgu,Ahn, Jong-Hyun,Cho, Jeong Ho American Chemical Society 2016 Chemistry of materials Vol.28 No.1
<P>We studied the surface-enhanced Raman scattering of an organic fluoropore (Rhodamine 6G, R6G) monolayer adsorbed onto graphene and two-dimensional (2D) molybedenium disulfides (MoS2) phototransistors and compared the results with the Raman scattering of R6G on 2D tungsten diselenides system (WSe2). The Raman enhancement factor of the R6G film adsorbed onto WSe2 was comparable to the corresponding value on graphene at 1365 cm(-1) and was approximately twice this value at 615 cm(-1). The amplitude of the charge transfer was estimated in situ by measuring the photocurrent produced in a hybrid system consisting of physisorbed R6G layer and the 2D materials. We found that the enhanced Raman scattering of R6G adsorbed onto the 2D materials was closely correlated with the charge transfer between the adsorbed molecules and the 2D materials. We also revealed that the intensity of Raman scattering generally decreased as the layer number of the 2D materials increased. For the R6G on the MoS2 nanosheet, a single layer system provided a maximum Raman enhancement factor, and this value decreased pseudolinearly with the number of layers. By contrast, the Raman enhancement factor of the R6G on WSe2 was greatest for both the mono- and bilayers, and it decreased dramatically as the number of layers increased. We provide qualitative theoretical explanations for these trends based on the electric field enhancement for the multile Fresnel phases and energy band diagrams of both systems.</P>