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Fabrication of Stretchable Transparent Electrodes

  • Oh, Jong Sik;Yeom, Geun Young
    • Applied Science and Convergence Technology
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    • v.26 no.6
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    • pp.149-156
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    • 2017
  • Recently, stretchable and transparent electrodes have received great attention owing to their potential for realizing wearable electronics. Unlike the traditional transparent electrodes represented by indium tin oxide (ITO), stretchable and transparent electrodes are able to maintain their electrical and mechanical properties even under stretching stress. Lots of research efforts have been dedicated to the development of stretchable and transparent electrodes since they represent the most important engineering platform for the production of wearable electronics. Various approaches using silver nanowires, nanostructured networks, conductive polymers, and carbon-based electrodes have been explored by many world leading research groups. In this review, present and recent advances in the fabrication methods of stretchable and transparent electrodes are discussed.

Parametric Characterization of Zinc Oxide Nanostructures Forming Three-Dimensional Hybrid Nanoarchitectures on Carbon Nanotube Constructs (산화아연 나노구조의 탄소나노튜브와의 혼성구조 형성 특성 연구)

  • Ok, Jong G.
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.39 no.6
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    • pp.541-548
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    • 2015
  • We study the structural and functional characteristics of zinc oxide (ZnO) nanostructures that are grown on carbon nanotube (CNT) constructs via step-wise chemical vapor deposition (CVD). First, we optimize the CVD process to directly grow ZnO nanostructures on CNTs by controlling the growth temperature below $600^{\circ}C$, where CNTs can be sustained in a ZnO-growing oxidative atmosphere. We then investigate how the morphology and areal density of ZnO nanostructures evolve depending on process parameters, such as pressure, temperature, and gas feeding composition, while focusing on the effect of underlying CNT topology on ZnO nucleation and growth. Because various types of ZnO nanostructures, including nanowires, nanorods, nanoplates, and polycrystalline nanocrystals, can be conformally formed on highly conductive CNT platforms, this electrically addressable three-dimensional hybrid nanoarchitecture may better meet a wide range of nanoelectronic application-specific needs.

NO Gas Sensing Properties of ZnO-SWCNT Composites (산화아연-단일벽탄소나노튜브복합체의 일산화질소 감지 특성)

  • Jang, Dong-Mi;Ahn, Se-Yong;Jung, Hyuck;Kim, Do-Jin
    • Korean Journal of Materials Research
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    • v.20 no.11
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    • pp.623-627
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    • 2010
  • Semiconducting metal oxides have been frequently used as gas sensing materials. While zinc oxide is a popular material for such applications, structures such as nanowires, nanorods and nanotubes, due to their large surface area, are natural candidates for use as gas sensors of higher sensitivity. The compound ZnO has been studied, due to its chemical and thermal stability, for use as an n-type semiconducting gas sensor. ZnO has a large exciton binding energy and a large bandgap energy at room temperature. Also, ZnO is sensitive to toxic and combustible gases. The NO gas properties of zinc oxide-single wall carbon nanotube (ZnO-SWCNT) composites were investigated. Fabrication includes the deposition of porous SWCNTs on thermally oxidized $SiO_2$ substrates followed by sputter deposition of Zn and thermal oxidation at $400^{\circ}C$ in oxygen. The Zn films were controlled to 50 nm thicknesses. The effects of microstructure and gas sensing properties were studied for process optimization through comparison of ZnO-SWCNT composites with ZnO film. The basic sensor response behavior to 10 ppm NO gas were checked at different operation temperatures in the range of $150-300^{\circ}C$. The highest sensor responses were observed at $300^{\circ}C$ in ZnO film and $250^{\circ}C$ in ZnO-SWCNT composites. The ZnO-SWCNT composite sensor showed a sensor response (~1300%) five times higher than that of pure ZnO thin film sensors at an operation temperature of $250^{\circ}C$.

Efficient Electron Transfer in CdSe-py-SWNTs FETs

  • Jeong, So-Hee;Shim, H.C.;Han, Chang-Soo
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.63-63
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    • 2010
  • Ability to transport extracted carriers from NQDs is essential for the development of most NQD based applications. Strategies to facilitate carrier transport while preserving NQDs' optical characteristics include: 1) Fabricating neat films of NQDs with modified surfaces either by adapting series of ligands with certain limitations or by applying physical processes such as heat annealing 2) Coupling of NQDs to one-dimensional nanostructures such as single walled carbon nanotubes (SWNTs) or various types of nanowires. NQD-nanowire hybrid nanostructures are expected to facilitate selective wavelength absorption, charge transfer to 1-D nanostructures, and efficient carrier transport. Even with the vast interests in using NQD-SWNT hybrid materials in optoelectric applications, still, no reports so far have clearly elucidated the optoelectric behavior when they were assembled on the FET mainly because the complexity involving in both components in their preparation and characterization. We have monitored the optical properties of both components (NQDs, SWNTs) from the synthesis, to the assembly, and to the device. More importantly, by using pyridine molecules as a linker to non-covalently attach NQDs to SWNTs, we were able to assemble NQDs on SWNTs with precise density control without harming their electronic structures. Furthermore, by measuring electrical signals from the fabricated aligned SWNTs-FET using dielectrophoresis (DEP), we were able to elucidate the charge transfer mechanism.

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Electrosynthesized poly(1,5-diaminonaphthalene)/polypyrrole nanowires bilayer as an immunosensor platform for breast cancer biomarker CA 15-3

  • Nguyen, Van-Anh;Nguyen, Huy L.;Nguyen, Dzung T.;Do, Quan P.;Tran, Lam D.
    • Current Applied Physics
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    • v.17 no.11
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    • pp.1422-1429
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    • 2017
  • In this paper, an electrosynthesized bilayer film of polypyrrole nanowire and poly(1,5-diaminonaphthalene) on a disposable screen-printing carbon ink electrode is presented. The inner polypyrrole nanowire layer had a large surface-to-volume ratio and high conductivity in the neutral medium, whereas the outer layer of poly(1,5diaminonaphthalene) had functional amino groups on the polymer chains. The combination of polypyrrole nanowire and poly(1,5diaminonaphthalene) showed a promising material for electrochemical biosensing. Here we reported an electrochemical immunosensor based on this approach for the purpose of detecting breast cancer biomarkers. The bilayer could enhance the surface coverage of antibody anti-CA 15-3 and consequently improve the sensitivity and stability of the immunosensors. The magnetic beads were used as carriers of labeled antibody anti-CA15-3 and HRP (horseradish peroxidase) in order to achieve an amplification of the signal. Under optimized conditions, the linear range of the immunoassay was $0.05-20U\;mL^{-1}$ with a detection limit of $0.02U\;mL^{-1}$ CA 15-3 antigen.

Detection of H2S Gas with CuO Nanowire Sensor (산화구리 나노선 센서의 황화수소 감지특성)

  • Lee, Dongsuk;Kim, Dojin;Kim, Hyojin
    • Korean Journal of Materials Research
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    • v.25 no.5
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    • pp.238-246
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    • 2015
  • $H_2S$ is a flammable toxic gas that can be produced in plants, mines, and industries and is especially fatal to human body. In this study, CuO nanowire structure with high porosity was fabricated by deposition of copper on highly porous singlewall carbon nanotube (SWCNT) template followed by oxidation. The SWCNT template was formed on alumina substrates by the arc-discharge method. The oxidation temperatures for Cu nanowires were varied from 400 to $800^{\circ}C$. The morphology and sensing properties of the CuO nanowire sensor were characterized by FESEM, Raman spectroscopy, XPS, XRD, and currentvoltage examination. The $H_2S$ gas sensing properties were carried out at different operating temperatures using dry air as the carrier gas. The CuO nanowire structure oxidized at $800^{\circ}C$ showed the highest response at the lowest operating temperature of $150^{\circ}C$. The optimum operating temperature was shifted to higher temperature to $300^{\circ}C$ as the oxidation temperature was lowered. The results were discussed based on the mechanisms of the reaction with ionosorbed oxygen and the CuS formation reaction on the surface.

Novel Enhanced Flexibility of ZnO Nanowires Based Nanogenerators Using Transparent Flexible Top Electrode

  • Gang, Mul-Gyeol;Ha, In-Ho;Kim, Seong-Hyeon;Jo, Jin-U;Ju, Byeong-Gwon;Lee, Cheol-Seung
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.490.1-490.1
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    • 2014
  • The ZnO nanowire (NW)-based nanogenerators (NGs) can have rectifying current and potential generated by the coupled piezoelectric and semiconducting properties of ZnO by variety of external stimulation such as pushing, bending and stretching. So, ZnO NGs needed to enhance durability for stable properties of NGs. The durability of the metal electrodes used in the typical ZnO nanogenerators(NGs) is unstable for both electrical and mechanical stability. Indium tin oxide (ITO) is used as transparent flexible electrode but because of high cost and limited supply of indium, the fragility and lack of flexibility of ITO layers, alternatives are being sought. It is expected that carbon nanotube and Ag nanowire conductive coatings could be a prospective replacement. In this work, we demonstrated transparent flexible ZnO NGs by using CNT/Ag nanowire hybrid electrode, in which electrical and mechanical stability of top electrode has been improved. We grew vertical type ZnO NW by hydrothermal method and ZnO NW was coated with hybrid silicone coating solution as capping layer to enhance adhesion and durability of ZNW. We coated the CNT/Ag nanowire hybrid electrode by using bar coating system on a capping layer. Power generation of the ZnO NG is measured by using a picoammeter, a oscilloscope and confirmed surface condition with FE-SEM. As a results, the NGs using the CNT/Ag NW hybrid electrode show 75% transparency at wavelength 550 nm and small change of the resistance of the electrode after bending test. It will be discussed the effect of the improved flexibility of top electrode on power generation enhancement of ZnO NGs.

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Technology of Flexible Transparent Conductive Electrode for Flexible Electronic Devices (유연전자소자를 위한 차세대 유연 투명전극의 개발 동향)

  • Kim, Joo-Hyun;Chon, Min-Woo;Choa, Sung-Hoon
    • Journal of the Microelectronics and Packaging Society
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    • v.21 no.2
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    • pp.1-11
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    • 2014
  • Flexible transparent conductive electrodes (TCEs) have recently attracted a great deal of attention owing to rapid advances in flexible electronic devices, such as flexible displays, flexible photovoltanics, and e-papers. As the performance and reliability of flexible electronics are critically affected by the quality of TCE films, it is imperative to develop TCE films with low resistivity and high transparency as well as high flexibility. Indium tin oxide (ITO) has been the most dominant transparent conducting material due to its high optical transparency and electrical conductivity. However, ITO is susceptible to cracking and delamination when it is bent or deformed. Therefore, various types of flexible TCEs, such as carbon nanotube, conducting polymers, graphene, metal mesh, Ag nanowires (NWs), and metal mesh have been extensively investigated. Among several options to replace ITO film, Ag NWs and metal mesh have been suggested as the promising candidate for flexible TCEs. In this paper, we focused on Ag NWs and metal mesh, and summarized the current development status of Ag NWs and metal mesh. The several critical issues such as high contact resistance and haze are discussed, and newly developed technologies to resolve these issues are also presented. In particular, the flexibility and durability of Ag NWs and metal mesh was compared with ITO electrode.

Improving Conductivity of Metal Grids by Controlling Sintering Process (배선 함몰 전극의 배선 소결공정 최적화에 따른 전기적 특성 향상)

  • Ahn, Wonmin;Jung, Sunghoon;Kim, Do-Geun
    • Journal of the Korean institute of surface engineering
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    • v.48 no.4
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    • pp.158-162
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    • 2015
  • To substitute indium tin oxide (ITO), many substituents have been studied such as metal nanowires, carbon based materials, 2D materials, and conducting polymers. These materials are not good enough to apply to an electrode because theses exhibit relatively high resistance. So metal grids are required as an additionalelectrode to improve the conductivities of substituents. The metal grids were printed by electrohydrodynamic printing system using Ag nanoparticle based ink. The Ag grids showed high uniformity and the line width was about $10{\mu}m$. The Ag nanoparticles are surrounded by dispersants such as unimolecular and polymer to prevent aggregation between Ag nanoparticles. The dispersants lead to low conductivity of Ag grids. Thus, the sintering process of Ag nanoparticles is strongly recommended to remove dispersants and connect each nanoparticles. For sintering process, the interface and microstructure of the Ag grid were controlled in 1.0 torr Ar atmosphere at aound $400^{\circ}C$ of temperature. From the sintering process, the uniformity of the Ag grid was improved and the defects on the Ag grids were reduced. As a result, the resistivity of Ag grid was greatly reduced up to $5.03({\pm}0.10){\times}10^{-6}{\Omega}{\cdot}cm$. The metal grids embedded substrates containing low pressure Ar sintered Ag grids showed 90.4% of transmittance in visible range with $0.43{\Omega}/{\square}$ of sheet resistance.

Characterization of SiC nanowire Synthesized by Thermal CVD (열 화학기상증착법을 이용한 탄화규소 나노선의 합성 및 특성연구)

  • Jung, M.W.;Kim, M.K.;Song, W.;Jung, D.S.;Choi, W.C.;Park, C.J.
    • Journal of the Korean Vacuum Society
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    • v.19 no.4
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    • pp.307-313
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    • 2010
  • One-dimensional cubic phase silicon carbide nanowires (${\beta}$-SiC NWs) were efficiently synthesized by thermal chemical vapor deposition (TCVD) with mixtures containing Si powders and nickel chloride hexahydrate $(NiCl_2{\cdot}6H_2O)$ in an alumina boat with a carbon source of methane $(CH_4)$ gas. SEM images are shown that the growth temperature (T) of $1,300^{\circ}C$ is not enough to synthesize the SiC NWs owing to insufficient thermal energy for melting down a Si powder and decomposing the methane gas. However, the SiC NWs could be synthesized at T>$1,300^{\circ}C$ and the most efficient temperature for growth of SiC NWs is T=$1,400^{\circ}C$. The synthesized SiC NWs have the diameter with an average range between 50~150 nm. Raman spectra clearly revealed that the synthesized SiC NWs are forming of a cubic phase (${\beta}$-SiC). Two distinct peaks at 795 and $970 cm^{-1}$ in Raman spectra of the synthesized SiC NWs at T=$1,400^{\circ}C$ represent the TO and LO mode of the bulk ${\beta}$-SiC, respectively. XRD spectra are also supported to the Raman spectra resulting in the strongest (111) peaks at $2{\Theta}=35.7^{\circ}$, which is the (111) plane peak position of 3C-SiC. Moreover, the gas flow rate of 300 sccm for methane is the optimal condition for synthesis of a large amount of ${\beta}$-SiC NW without producing the amorphous carbon structure shown at a high methane flow rate of 800 sccm. TEM images are shown two kinds of the synthesized ${\beta}$-SiC NWs structures. One is shown the defect-free ${\beta}$-SiC NWs with a (111) interplane distance of 0.25 nm, and the other is the stacking-faulted ${\beta}$-SiC NWs. Also, TEM images exhibited that two distinct SiC NWs are uniformly covered with $SiO_2$ layer with a thickness of less 2 nm.