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John G. Fisher,Ha-Young Park,Yeo-Ok Song,Sun-Joong Baek,Hung Vu,Jee-Hoon Kim,Young-Hun Kim,Jong-Sook Lee 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.1
The effect of sintering temperature on the densification, microstructure and structure of 0.4(Bi0.5K0.5)TiO3-0.6BiFeO3 lead-free piezoelectric ceramics is assessed. The 0.4(Bi0.5K0.5)TiO3- 0.6BiFeO3 powders were prepared by using the mixed-oxide method and were sintered at temperatures of 1000, 1050 and 1100 C for 1 to 5 hrs. Unlike earlier work, the sintered samples showed high densities even when sintered at 1000 C. X-ray diffraction revealed that the sintered samples shared the same rhombohedral structure as BiFeO3. With increasing sintering temperature, the rhombohedral distortion of the unit cell decreased. In addition to the relaxor-like broad peak around 400 C, a low-temperature dielectric peak was found at temperatures below 190 C by employing a low-frequency sweep down to 10 mHz. The DC conductivity of the 0.4(Bi0.5K0.5)TiO3-0.6BiFeO3 sample exhibited three temperature regions with activation energy values of 0.56 eV (T > 500 C), 0.72 eV (400 C < T <200 C) and 0.81 eV (T < 190 C). The characteristic transitions in the conductivity could be related to the N´eel temperature (370 C) and the conductivity anomaly observed at ca. 190 C in BiFeO3.
탄소나노튜브-금속산화물 나노와이어의 3차원 혼성 나노구조 형성 및 응용
옥종걸(Jong G. Ok),A. John Hart,L. Jay Guo 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
We present the assembly and application of three-dimensional (3D) hybrid nanoarchitectures comprising carbon nanotubes (CNTs) and metal oxide (MOx) nanowires such as zinc oxide and vanadium oxide. The MOx nanowires are hierarchically assembled onto the surface of aligned or textured CNT constructs via the step-wise chemical vapor deposition (CVD) process at the temperature CNTs are free from oxidative degradation. Since the conformal highdensity MOx nanowires can be directly connected to highly conducting CNT framework over large interfacial area, the electrical response originating from functional MOx upon external stimuli can be rapidly and efficiently collected through the CNT framework, leading to many applications ranging from fast-responsive sensors to energy converters.
산화아연 나노구조의 탄소나노튜브와의 혼성구조 형성 특성 연구
옥종걸(Jong G. Ok) 대한기계학회 2015 大韓機械學會論文集B Vol.39 No.6
본 논문에서는 순차적 화학기상증착법에 기반하여 다양한 구조적 특성을 갖는 산화아연 나노구조체를 탄소나노튜브 상에 3 차원 혼성구조로 형성하는 공정을 개발하고 그 형성 메커니즘을 논한다. 이어서 나노와이어, 나노로드, 나노플레이트, 다결정 나노박막 등 다양한 형상의 산화아연 나노구조를 온도, 압력, 개스유량 등 주요 파라미터들의 조절을 통해 형성할 수 있음을 보이며, 이의 형성 원리에 대해 기본적인 형성 메커니즘과 연계하여 고찰한다. 본 연구 결과를 통해, 압전 및 광전 에너지변환 특성 등 풍부한 기능성을 보유하되 다소 높은 전기저항을 갖는 산화아연 나노구조체를 다양한 포맷으로 양전도성의 탄소나노튜브와 혼성화 함으로써, 각각의 포맷 별로 특화된 보다 폭넓은 응용 분야로의 활용을 구현해 나갈 수 있을 것이다. 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 °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.
Park, Sei Jin,Ok, Jong G.,Park, Hui Joon,Lee, Kyu-Tae,Lee, Jae Hyuk,Kim, Jeong Dae,Cho, Eikhyun,Baac, Hyoung Won,Kang, Shinill,Guo, L. Jay,Hart, A. John Elsevier 2018 Carbon Vol.129 No.-
<P><B>Abstract</B></P> <P>The unique properties of carbon nanotubes (CNTs) allow them to be used in various optical applications, such as ultra-dark surfaces, bolometers, metamaterial cloaks, and anisotropic absorbers. In particular, organization of CNTs with controlled density at the sub-micrometer scale could enable new strategies to engineer optically active surfaces. Here, we present a new strategy to engineer the density-dependent optical properties of CNT forests by patterning of catalyst film via nanoimprint lithography (NIL) followed by atmospheric pressure chemical vapor deposition (CVD) synthesis of CNTs. Via this approach, we demonstrate atmospheric pressure growth of CNT structures with widths of 80–350 nm. These structures form self-supporting arrays with height exceeding 500 μm, representing aspect ratios well over 1000:1. Optical attenuation measurement places the density of NIL patterned forests to be a fraction of the density of unpatterned CNT forests, confirming that the CNT density is effectively controlled by the catalyst coverage. The infrared absorbance measurements corroborate the density control, and Kramers-Kronig analysis shows that the refractive indices of the NIL patterned CNT forests are tunable in the range of 1–1.8.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Nanopatterning on the cylindrical surface using an E-beam pre-mapping algorithm
Lee, Chang Rin,Ok, Jong G,Jeong, Myung Yung IOP 2019 Journal of micromechanics and microengineering Vol.29 No.1
<P>Lithography technology has advanced from flat plates to cylindrical surfaces, aiming to address the emerging needs in flexible and mass-customized applications. Nanoscale ultra-precise patterns have benefited from advanced lithography techniques also involving precision stage technology and material development. While conventional lithography mostly relies on flat wafer-base processing, fabricating nanopatterns on cylindrical surfaces can further expand the applicability and productivity of nanoscale lithography, for example, by integrating with the continuous and scalable plate-to-roll or roll-to-roll nanopatterning techniques. In this regard, we develop a novel nanopatterning methodology that can directly create a nanoscale pattern on the surface of a cylindrical mould by utilizing the E-beam pre-mapping algorithm for uniform E-beam exposure. Here, E-beam pre-mapping was employed to ensure uniform exposure over the cylindrical surface from the planar E-beam source, where the trajectory of the E-beam is modulated along the curved surface of the cylinder based on the pre-calibration of the surface profile. We design and build up a cylindrical exposure system with an E-beam gun that can move at a high degree of freedom. We also perform in-depth analytic modelling and profiling of the target curved surface, which is an essential step for applying E-beam pre-mapping for uniform exposure. By conducting the developed process, we finally achieve a very fine 60 nm scale half-pitch pattern on the cylindrical surface, which may be further extended to enable direct nanopatterning on curved surfaces for many unique applications.</P>