Browsing by Author "Huang, Chun-Wei"

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Atomic Imaging of Molybdenum Oxide Nanowires with Unique and Complex Periodicity by Advanced Electron Microscopy
(2020-03-11)
Ting, Yi-Hsin
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Huang, Chun-Wei
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Yasuhara, Akira
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Chen, Sheng-Yuan
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Chen, Jui-Yuan
Crystalline Mo5O14 exhibits distinctive structural features such as tunnel structure and pseudolamellar arrangement according to the ideal model. However, the spatial resolution of the conventional technique of transmission electron microscopy (TEM) is insufficient to distinguish the actual positions of atoms. In this work, we aimed to systematically analyze and identify the Mo5O14 nanowires fabricated by the chemical vapor deposition (CVD) process. Utilizing high-angle annular dark-field (HAADF), annular bright-field (ABF), and enhanced annular bright-field (E-ABF) within the scanning transmission electron microscope (STEM) mode reveals the structural features at the atomic scale. In addition, the ultrahigh resolution images have confirmed the crystallographic insights in [001] growth direction for the Mo5O14 nanowires with a tunnel structure throughout the nanowire. The cross-sectional images show the unique close-packed plane and atomic arrangement with a network of MoO6 octahedra and MoO7 pentagonal bipyramids. These results are consistent with the theoretical atomic arrangement, supporting the realization of Mo5O14-type catalysts used in the selective oxidation process and battery applications.
Atomic Visualization of the Phase Transition in Highly Strained BiFeO3 Thin Films with Excellent Pyroelectric Response
(2015-10-01)
Chiu, Chung-Hua
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Liang, Wen-I
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Huang, Chun-Wei
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Chen, Jul-Yuan
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Liu, Yun-Ya
Great attention is paid to that stimulus response of materials, which is a prerequisite for energy harvesting applications. Driven by advances in nanotechnology, the atomic motions, involved in phase transitions and associated with stimulus responses, require detailed investigation on the nanoscale. Recently, strain engineering of BiFeO3 (BFO) has become the subject of broad research interest due to its promising potential in energy conversion applications, such as piezoelectric, pyroelectric and shape memory effect (SME) devices. In this study, an excellent pyroelectric response is associated with reversible phase transitions in mixed-phase BFO films using thermal stimuli. Using an in situ high-resolution transmission electron microscope (HRTEM), we observed that phase transition between rhombohedral-like (R-like) and tetragonal-like (1-like) BFO involved the migration of the phase boundary, which is a prerequisite for the growth of the T-like phase and requires an intermediate phase. Moreover, the origin of the phase transition is attributed to competition between thermodynamic stability and substrate-induced strain, as suggested by phase-field simulations. The results provide a fundamental understanding of the atomic processes that underlie the stimulus response of the strained BFO films and demonstrate the potential of this extraordinary material for novel energy harvesting applications. (C) 2015 Elsevier Ltd. All rights reserved.
Atomic-Scale Fabrication of In-Plane Heterojunctions of Few-Layer MoS2 via In Situ Scanning Transmission Electron Microscopy
(1970-01-01)
Tai, Kuo-Lun
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Huang, Chun-Wei
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Cai, Ren-Fong
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Huang, Guan-Min
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Tseng, Yi-Tang
Layered MoS2 is a prospective candidate for use in energy harvesting, valleytronics, and nanoelectronics. Its properties strongly related to its stacking configuration and the number of layers. Due to its atomically thin nature, understanding the atomic-level and structural modifications of 2D transition metal dichalcogenides is still underdeveloped, particularly the spatial control and selective precision. Therefore, the development of nanofabrication techniques is essential. Here, an atomic-scale approach used to sculpt 2D few-layer MoS2 into lateral heterojunctions via in situ scanning/transmission electron microscopy (STEM/TEM) is developed. The dynamic evolution is tracked using ultrafast and high-resolution filming equipment. The assembly behaviors inherent to few-layer 2D-materials are observed during the process and included the following: scrolling, folding, etching, and restructuring. Atomic resolution STEM is employed to identify the layer variation and stacking sequence for this new 2D-architecture. Subsequent energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy analyses are performed to corroborate the elemental distribution. This sculpting technique that is established allows for the formation of sub-10 nm features, produces diverse nanostructures, and preserves the crystallinity of the material. The lateral heterointerfaces created in this study also pave the way for the design of quantum-relevant geometries, flexible optoelectronics, and energy storage devices.
Atomic-Scale Localized Thinning and Reconstruction of Two-Dimensional WS2 Layers through In Situ Transmission Electron Microscopy/Scanning Transmission Electron Microscopy
(2020-07-09)
Tseng, Yi-Tang
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Tai, Kuo-Lun
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Huang, Chun-Wei
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Huang, Chih-Yang
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Wu, Wen-Wei
Subnanometer nanofabrication has been investigated, and electron beam processing has been found to be a suitable strategy to control nanoparticle organization over large areas. Organized nanostructures have demonstrated their potential for technological applications. Here, we focus on the processing of tungsten disulfide (WS2) due to its novelty and promising electronic properties for further development of functional devices. First, we summarize the theory of electron beam irradiation by surveying the dynamic behaviors observed during in situ experiments. In particular, the diverse structures with various numbers of layers derived from localized thinning produce considerable lateral heterointerfaces. The generation of the intriguing tungsten-rich cluster is also consistent with the mechanism of our atomic engineering experiments. These findings suggest a method for the electron beam processing of 2D materials and demonstrate the viability of atomic engineering using electron irradiation.
Carbon Nanotube/Nitrogen-Doped Reduced Graphene Oxide Nanocomposites and Their Application in Supercapacitors
(2017-08-01)
Yang, Chih-Chieh
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Tsai, Meng-Han
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Huang, Chun-Wei
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Yen, Po-Jen
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Pan, Chien-Chung
Electrodes of carbon-based nanocomposites with high specific surface areas and suitable pore sizes have high potential for improving power and energy densities of supercapacitors. In this study, nitrogen-doped reduced graphene oxide (NrGO) nanosheets were synthesized to increase the specific surface area of reduced graphene oxide (rGO). The specific surface area of NrGO was increased to 633 m(2)g(-1) compared to that of rGO, 450 m(2)g(-1). A series of NrGO/carbon nanotubes (CNTs) nanocomposites were prepared. By using NrGO/CNTs/polyvinylidene difluoride (PVDF)/carbon black/N-methyl-pyrrolidone (NMP) nanocomposites as both of anode and cathode into two electrodes, such symmetric supercapacitor in the 1 M KOH aqueous electrolyte exhibited high specific capacitance (227 F g(-1) at 20 mV s(-1)), fast rate capability (83% capacitance of current density 1 mA cm(-2) at current density 5 mA cm(-2)), low resistance (0.98 Omega), and excellent cycling stability (87% capacitance retention after 10,000 charge/discharge cycles). Moreover, the symmetric supercapacitor in the ionic liquid (BMIMTFSI) electrolyte possessed a wide operating voltage (3 V) and high energy density (89 Wh kg(-1) at 1 mA cm(-2)). The carbon-based hybrid electrode has high potential for use in energy storage and conversion devices.
Copper silicide/silicon nanowire heterostructures: in situ TEM observation of growth behaviors and electron transport properties
(2013)
Chiu, Chung-Hua
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Huang, Chun-Wei
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Chen, Jui-Yuan
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Huang, Yu-Ting
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Hu, Jung-Chih
Copper silicide has been studied in the applications of electronic devices and catalysts. In this study, Cu3Si/Si nanowire heterostructures were fabricated through solid state reaction in an in situ transmission electron microscope (TEM). The dynamic diffusion of the copper atoms in the growth process and the formation mechanism are characterized. We found that two dimensional stacking faults (SF) may retard the growth of Cu3Si. Due to the evidence of the block of edge-nucleation (heterogeneous) by the surface oxide, center-nucleation (homogeneous) is suggested to dominate the silicidation. Furthermore, the electrical transport properties of various silicon channel length with Cu3Si/Si heterostructure interfaces and metallic Cu3Si NWs have been investigated. The observations not only provided an alternative pathway to explore the formation mechanisms and interface properties of Cu3Si/Si, but also suggested the potential application of Cu3Si at nanoscale for future processing in nanotechnology.
Design of AC-Coupled Circuit for High-speed Interconnects
(2012)
Huang, Chun-Wei
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Liu, Kai-Jen
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Huang, Yu-Jung
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Chen, Ming-Kun
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Lin, Yi-Lung
The scaling of semiconductor technology together with 3D IC stacking integration make it possible for many portable electronics to process large amount of multimedia data. AC-coupling enables chip placed face-to-face for signal transmission using close-field capacitive coupling. A high performance system design using AC coupled interconnect (ACCI) technology not only achieves shorter and faster interconnection between dies but also increases packaging density. This paper describes a chip-to-chip circuit design suitable for high-speed 3DIC interconnected applications. The AC-Coupled face-to-face (F2F) chip was simulated using HSPICE with TSMC 0.18-mu m 1P6M CMOS technology process file under a 1.8 V supply voltage. The simulation results indicated the proposed circuit with the self-test characteristics can achieve differential signal transmission up to 2.5 Gbps.
Developing a Conjunctive Use Optimization Model for Allocating Surface and Subsurface Water in an Off-Stream Artificial Lake System
(2016-08-01)
Pan, Chen-Che
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Chen, Yu-Wen
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Chang, Liang-Cheng
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Huang, Chun-Wei
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土木工程學系
This work develops a rule curve-based conjunctive use management model for optimizing the operating rules for a lake-groundwater system with off-stream storage lakes. The proposed procedure is a simulation-optimization approach that embeds an Artificial Neural Network ( ANN) instead of a groundwater numerical model into a genetic algorithm ( GA). The direct physical exchange between lake water with groundwater is simulated using the ANN model, which is a reduced version of a full numerical model, MODFLOW with an LAK3 module. By applying the ANN model, the proposed procedure can reduce the computational burden that is induced by the nonlinear exchange. An operating rule-based optimal conjunctive use management model for the Gaopin Artificial lakes system in Taiwan was thus developed using the proposed framework. A set of optimal solutions involves rule curves and a discount ratio. Simulation results demonstrate that the embedded ANN model can accurately simulate the nonlinear exchange of a lake with groundwater. The embedded ANN model is less computationally complex than the numerical model. This work demonstrates a methodology for reducing the computational burden of the optimal conjunctive use management model that is associated with an internal nonlinear system by using the ANN reduced model. Specifically, the concept of, and results obtained using the developed operating rule-based model incorporating five artificial lakes and considering the nonlinear exchange of those lakes with the groundwater system provides a valuable practical reference for solving related conjunctive use problems.
Dielectric Engineering of a Boron Nitride/Hafnium Oxide Heterostructure for High-Performance 2D Field Effect Transistors
(2016-03-09)
Zou, Xuming
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Huang, Chun-Wei
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Wang, Lifeng
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Yin, Long-Jing
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Li, Wenqing
A unique design of a hexagonal boron nitride (h-BN)/HfO2 dielectric heterostructure stack is demonstrated, with few-layer h-BN to alleviate the surface optical phonon scattering, followed by high-kappa HfO2 deposition to suppress Coulombic impurity scattering so that high-performance top-gated two-dimensional semiconductor transistors are achieved. Furthermore, this dielectric stack can also be extended to GaN-based transistors to enhance their performance.
Direct Observation of Dual-Filament Switching Behaviors in Ta2O5-Based Memristors
(2017-04-18)
Chang, Chia-Fu
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Chen, Jui-Yuan
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Huang, Chun-Wei
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Chiu, Chung-Hua
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Lin, Ting-Yi
Direct observation of melting behaviors at the nanoscale under electron beam and heat to form hollow nanostructures
(2012)
Huang, Chun-Wei
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Hsin, Cheng-Lun
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Wang, Chun-Wen
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Chu, Fu-Hsuan
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Kao, Chen-Yen
"We report the melting behaviours of ZnO nanowire by heating ZnO-Al2O3 core-shell heterostructures to form Al2O3 nanotubes in an in situ ultrahigh vacuum transmission electron microscope (UHV-TEM). When the ZnO-Al2O3 core-shell nanowire heterostructures were annealed at 600 degrees C under electron irradiation, the amorphous Al2O3 shell became single crystalline and then the ZnO core melted. The average vanishing rate of the ZnO core was measured to be 4.2 nm s(-1). The thickness of the Al2O3 nanotubes can be precisely controlled by the deposition process. Additionally, the inner geometry of nanotubes can be defined by the initial ZnO core. The result shows a promising method to obtain the biocompatible Al2O3 nanotubes, which may be applied in drug delivery, biochemistry and resistive switching random access memory (ReRAM)."
Direct Observation of Sublimation Behaviors in One-Dimensional In2Se3/In2O3 Nanoheterostructures
(2015-06-02)
Hsin, Cheng-Lun
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Huang, Chun-Wei
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Chen, Jui-Yuan
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Liao, Kuo-Cheng
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Liu, Po-Liang
Recently, in situ transmission electron microscopy (TEM) has provided a route to analyze structural characterization and chemical evolution with its powerful and unique applications. In this paper, we disclose the detailed phenomenon of sublimation on the atomic scale. In2Se3/In2O3 nanowires were synthesized via the vapor-liquid-solid mechanism and studied in an ultra-high-vacuum (UHV) TEM at high temperature in real time. During in situ observation of the sublimation process of the nanowires, the evolution and reconstruction of the exposed In2Se3 surface progressed in different manners with time. The surface structure was decomposed by mass-desorption and stepwise-migration processes, which are also energetically favored processes in the ab initio calculation. This study developed a new concept and will be essential in the development of atomic kinetics.
Dynamic Evolution of Conducting Nanofilament in Resistive Switching Memories
(2013-08-01)
Chen, Jui-Yuan
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Hsin, Cheng-Lun
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Huang, Chun-Wei
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Chiu, Chung-Hua
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Huang, Yu-Ting
Resistive random access memory (ReRAM) has been considered the most promising next-generation nonvolatile memory. In recent years, the switching behavior has been widely reported, and understanding the switching mechanism can improve the stability and scalability of devices. We designed an innovative sample structure for in situ transmission electron microscopy (TEM) to observe the formation of conductive filaments in the Pt/ZnO/Pt structure in real time. The corresponding current-voltage measurements help us to understand the switching mechanism of ZnO film. In addition, high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) have been used to identify the atomic structure and components of the filament/disrupted region, determining that the conducting paths are caused by the conglomeration of zinc atoms. The behavior of resistive switching is due to the migration of oxygen ions, leading to transformation between Zn-dominated ZnO1-x and ZnO.
Dynamic Observation of Phase Transformation Behaviors in Indium(III) Selenide Nanowire Based Phase Change Memory
(2014-09-01)
Huang, Yu-Ling
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Huang, Chun-Wei
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Chen, Jui-Yuan
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Ting, Yi-Hsin
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Lu, Kuo-Chang
Phase change random access memory (PCRAM) has been extensively investigated for its potential applications in next-generation nonvolatile memory. In this study, indium(III) selenide (In2Se3) was selected due to its high resistivity ratio and lower programming current. Au/In2Se3-nanowire/Au phase change memory devices were fabricated and measured systematically in an in situ transmission electron microscope to perform a RESET/SET process under pulsed and dc voltage swept mode, respectively. During the switching, we observed the dynamic evolution of the phase transformation process. The switching behavior resulted from crystalline/amorphous change and revealed that a long pulse width would induce the amorphous or polycrystalline state by different pulse amplitudes, supporting the improvement of the writing speed, retention, and endurance of PCRAM.
Dynamic observation of reversible lithium storage phenomena in hybrid supercapacitor devices
(2017-11-01)
Huang, Guan-Min
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Tsai, Tsung-Chun
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Huang, Chun-Wei
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Kumar, Nagesh
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Tseng, Tseung-Yuen
Carbonaceous composites have attracted much attention as electrode materials for hybrid supercapacitors. Additionally, transition metal oxides, such as Co3O4, have high specific capacitance in the charging/discharging process. Here, we investigated the lithium storage mechanism of Co3O4/CNTs material via in situ transmission electron microscopy (TEM). Additionally, we analyzed the structure and composition of the anode material by high-resolution TEM, electron diffraction, energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS). Using our unique in situ experimental setup that employs colloidal electrolyte, we elucidate two different mechanisms during operation, including the electrochemical reaction (battery-type) and ions intercalation (supercapacitor-type) of the electrode material. The cube-like Co3O4 nanoparticles were converted to Co nanograins dispersed in the Li2O matrix after the first charging cycle. Subsequent cycles presented a reversible reaction between Co/Li2O and CoO/Li2O. Furthermore, the porous structure of the CNTs and conservation of the Li2O matrix allow for the excellent ability to accommodate tremendous volume expansion, which enhances the life of hybrid supercapacitors. Our observations not only provide direct evidence of the electrochemical behavior but also improve the structure to promote enhanced performance for the application of hybrid supercapacitors.
Dynamic observation on the functional metal oxide conversion behaviors in Fe3O4/ZnO heterostructures
(2020-03-01)
Huang, Chih-Yang
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Tai, Kuo-Lun
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Huang, Chun-Wei
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Tseng, Yi-Tang
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Lo, Hung-Yang
We directly observed the atomic diffusion process of bilayered Fe/ZnO transforming into a Fe3O4/ZnO heterostructure. Significantly, we suggested a unique two-step route in which Fe diffused along [0001](znO) via boundaries of ZnO and then reacted along [(1) over bar2 (1) over bar0](ZnO). The specific orientation relationship of [0001(]ZnO)//[11 (1) over bar ]Fe3O4 could be precisely controlled. In addition, the formation of a ZnO/Fe3O4 heterostructure can be tuned in terms of reaction depth by controlling the annealing time. This study provided a novel nanofabricated method to produce oriented metal oxide heterostructures while visualizing the atomic mechanism of metal oxide formation, which allows for further investigation of promising devices. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Dynamic observation on the growth behaviors in manganese silicide/silicon nanowire heterostructures
(2015-01-01)
Hsieh, Yu-Hsun
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Chiu, Chung-Hua
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Huang, Chun-Wei
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Chen, Jui-Yuan
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Lin, Wan-Jhen
Metal silicide nanowires (NWs) are very interesting materials with diverse physical properties. Among the silicides, manganese silicide nanostructures have attracted wide attention due to their several potential applications, including in microelectronics, optoelectronics, spintronics and thermoelectric devices. In this work, we exhibited the formation of pure manganese silicide and manganese silicide/silicon nanowire heterostructures through solid state reaction with line contacts between manganese pads and silicon NWs. Dynamical process and phase characterization were investigated by in situ transmission electron microscopy (in situ TEM) and spherical aberration corrected scanning transmission electron microscopy (Cs-corrected STEM), respectively. The growth dynamics of the manganese silicide phase under thermal effects were systematically studied. Additionally, Al2O3, serving as the surface oxide, altered the growth behavior of the MnSi nanowire, enhancing the silicide/Si epitaxial growth and effecting the diffusion process in the silicon nanowire as well. In addition to fundamental science, this significant study has great potential in advancing future processing techniques in nanotechnology and related applications.
Electron Beam Irradiation-Induced Deoxidation and Atomic Flattening on the Copper Surface
(2019-10-30)
Lin, Ting-Yi
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Lee, Shih-Kuang
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Huang, Guan-Min
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Huang, Chun-Wei
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Tai, Kuo-Lun
Electron beam (e-beam) has been developed for nanomaterial observation and moreover to induce structural evolutions in atomic scale. In this work, we demonstrate the deoxidation of cuprous oxide (Cu2O) and the formation of an atomically flat surface on a Cu nanowire by e-beam irradiation. To develop e-beam irradiation applications, the relation between e-beam radiation and the atomic surface is significant. Through the density functional theory simulation of atomic sputtering, an obvious disparity in the sputtering threshold has been found under different structural conditions, which leads to different structural evolutions. Both surface deoxidation and atomic surface flattening reactions have been identified as self-limiting and irreversible processes via in situ transmission electron microscope observation. Under e-beam irradiation, the dynamic mechanism of atomic surface flattening is driven by the convergence of total surface energy and confirmed by climbing-image nudged elastic band (ci-NEB) calculations. With precise control, e-beam irradiation reveals enormous potentials in atomic surface engineering.
Excellent piezoelectric and electrical properties of lithium-doped ZnO nanowires for nanogenerator applications
(2014-09-01)
Chang, Yu-Tsui
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Chen, Jul-Yuan
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Yang, Tzu-Ping
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Huang, Chun-Wei
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Chiu, Chung-Hua
The well-aligned Li-doped zinc oxide nanowires (ZnO NWs) were successfully grown on Si substrates with seed layer by the hydrothermal method. The presence of Li in ZnO NWs is confirmed through EELS spectrum analysis. The acceptor energy level of the Li dopant is estimated to be 93.6 meV from the temperature-dependent PL spectra. From the SQUID measurements, the coercivity and saturation magnetization of the Li-doped ZnO NWs at room temperature are found to be 166 Oe and 9.64 memu/g, respectively. Additionally, the Li-doped ZnO NWFET confirms that the NWs were p-type with a high carrier mobility of 14.59 cm(2/)V s and an effective hole carrier concentration of 1.13 x 10(17) CM-3. The piezoelectric response of the Li-doped ZnO NWs produces much higher piezoelectric output current, voltage, and power than pure ZnO NWs. These results indicated that p-type ZnO NWs are a promising candidate for nanogenerator devices. (C) 2014 Elsevier Ltd. All rights reserved.
Flexible ferroelectric element based on van der Waals heteroepitaxy
(2017-06-01)
Jiang, Jie
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Bitla, Yugandhar
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Huang, Chun-Wei
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Thi Hien Do
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Liu, Heng-Jui
We present a promising technology for nonvolatile flexible electronic devices: A direct fabrication of epitaxial lead zirconium titanate (PZT) on flexible mica substrate via van der Waals epitaxy. These single-crystalline flexible ferroelectric PZT films not only retain their performance, reliability, and thermal stability comparable to those on rigid counterparts in tests of nonvolatile memory elements but also exhibit remarkable mechanical properties with robust operation in bent states (bending radii down to 2.5 mm) and cycling tests (1000 times). This study marks the technological advancement toward realizing much-awaited flexible yet single-crystalline nonvolatile electronic devices for the design and development of flexible, lightweight, and next-generation smart devices with potential applications in electronics, robotics, automotive, health care, industrial, and military systems.