Browsing by Author "Wu, Wen-Wei"

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A Strategy to Synthesize Ultrahigh-N-Doped Hierarchical Carbons via Induced beta-Sheet from Silk Fibroin by In Situ Electrogelation/Electropolymerization
(2020-04-27)
Liu, Ta-Chung
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Li, Tsung-Yu
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Hung, Pei-Sung
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Liang, Chun-Wei
;
Wu, Szu-Chen
Silk fibroin (SF) is recognized for its rich nitrogen content and has been explored for its promising potential in energy storage because of its hexagonal pseudographitic structure from the direct transformation of the unique secondary protein beta-sheet peptides of carbonized SF. In this work, we proposed a novel strategy that combined with in situ electrophoresis and electrogelation of SF as well as the electropolymerization of 3,4-ethylenedioxythiophene (EDOT) for producing high-level nitrogen-doped (N-doped) carbons. A high beta-sheet content of SF can be synthesized in a three-dimensional (3D) inverse opaline skeleton via double-network microstructure (physical beta-sheet cross-linking and chemical PEDOT cross-linking) induced by the hydrophobic EDOTs. This synergistic effect regulating SF distribution and balancing the intra/intermoleeular hydrogen bonding among SF results in boosting beta-sheet contents. Herein, this 3D SF/PEDOT composite inverse opal (SPIO) exhibits a much ultrahigh-coneentrated beta-sheets (46.4%) compared to pure electrogelated SFIO with 16.4% of beta-sheets. After subsequent pyrolysis, a high-level (14.7%) N-doped pseudographitic carbon inverse opal is realized. For evaluation as a pseudocapacitor, this high-level N-doped pseudographitic carbon inverse opal shows a capacitance of 342 F g(-1) at 0.5 A g(-1) and a commendable energy density of 31.7 Wh kg(-1) at an ultrahigh power density of 25009 W kg(-1) (at 50 A g(-1)). After galvanostatic charging/discharging at 15 A g(-1) for 10000 cycles, the sample maintains an impressive capacitance retention of 89.8%.
A Triode Device with a Gate Controllable Schottky Barrier: Germanium Nanowire Transistors and Their Applications
(1970-01-01)
Lin, Che-Yi
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Chen, Chao-Fu
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Chang, Yuan-Ming
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Yang, Shih-Hsien
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Lee, Ko-Chun
Electrical contacts often dominate charge transport properties at the nanoscale because of considerable differences in nanoelectronic device interfaces arising from unique geometric and electrostatic features. Transistors with a tunable Schottky barrier between the metal and semiconductor interface might simplify circuit design. Here, germanium nanowire (Ge NW) transistors with Cu3Ge as source/drain contacts formed by both buffered oxide etching treatments and rapid thermal annealing are reported. The transistors based on this Cu3Ge/Ge/Cu3Ge heterostructure show ambipolar transistor behavior with a large on/off current ratio of more than 10(5) and 10(3) for the hole and electron regimes at room temperature, respectively. Investigations of temperature-dependent transport properties and low-frequency current fluctuations reveal that the tunable effective Schottky barriers of the Ge NW transistors accounted for the ambipolar behaviors. It is further shown that this ambipolarity can be used to realize binary-signal and data-storage functions, which greatly simplify circuit design compared with conventional technologies.
Applications of p-n homojunction ZnO nanowires to one-diode one-memristor RRAM arrays
(2020-10-01)
Chen, Jui-Yuan
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Wu, Min-Ci
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Ting, Yi-Hsin
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Lee, Wei-Che
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Yeh, Ping-Hung
Nanowire (NW) structure is superior at defining the direction of device due to its one-dimension feature. In this work, the p-n ZnO NWs were successfully synthesized, and were able to vertically grow on Ta2O5 substrate. Thus, the well-performed Au/p-n ZnO NWs/Ta2O5/Au one-diode one-memoristor device was fabricated. The p-n ZnO NWs not only exhibited excellent rectifying behavior, but also played the role of oxygen storing during filaments formation. Therefore, the low-leakage device aimed to build high-density crossbar arrays which was required for accelerating the combination of 5 G with AI in near future applications. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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.
Bioinspired Engineering of a Bacterium-Like Metal-Organic Framework for Cancer Immunotherapy
(1970-01-01)
Chen, Po-Ming
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Pan, Wen-Yu
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Miao, Yang-Bao
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Liu, Yu-Miao
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Luo, Po-Kai
Bacteria-mediated tumor therapy (BMTT) has been known for decades; however, its clinical use is inhibited by its association with infections. To address this issue, a spiky, bacterium-like metal-organic framework (MOF), which can replicate the functional responses of BMTT without its adverse side-effects, is proposed. MOFs are synthesized in a solvothermal reaction of aluminum sulfate, ruthenium chloride hydrate, and 2-aminoterephthalic acid; they have a spherical morphology or many nanospikes on their surfaces, depending on the reaction temperature. Both spherical and spiky MOFs can function as photothermal agents, converting absorbed optical energy into local heat. Owing to their higher surface area of interaction, spiky MOFs are more easily phagocytosed by macrophages than are spherical MOFs, strengthening their immune responses. Moreover, when injected intratumorally, spiky MOFs reside significantly longer than spherical ones, enabling their use in repeated photothermal treatments. The combination of in situ vaccination with intratumorally injected bacterium-like MOFs under exposure to an near-infrared laser and the immune checkpoint blockade of systemically administered alpha PD-1 is evaluated in tumor-bearing mice. The results indicate that the checkpoint blockade acts synergistically with in situ vaccination to provide diverse antitumor functions of BMTT, destroying a primary tumor and suppressing tumor recurrence and metastasis.
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.
Cobalt silicide nanocables grown on Co films: synthesis and physical properties
(2010-12-03)
Hsin, Cheng-Lun
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Yu, Shih-Ying
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Wu, Wen-Wei
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材料科學與工程學系
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Department of Materials Science and Engineering
Single-crystalline cobalt silicide/SiO(x) nanocables have been grown on Co thin films on an SiO(2) layer by a self-catalysis process via vapor-liquid-solid mechanism. The nanocables consist of a core of CoSi nanowires and a silicon oxide shell with a length of several tens of micrometers. In the confined space in the oxide shell, the CoSi phase is stable and free from agglomeration in samples annealed in air ambient at 900 degrees C for 1 h. The nanocable structure came to a clear conclusion that the thermal stability of the silicide nanowires can be resolved by the shell encapsulation. Cobalt silicide nanowires were obtained from the nanocable structure. The electrical properties of the CoSi nanowires have been found to be compatible with their thin film counterpart and a high maximum current density of the nanowires has been measured. One way to obtain silicate nanowires has been demonstrated. The silicate compound, which is composed of cobalt, silicon and oxygen, was achieved. The Co silicide/oxide nanocables are potentially useful as a key component of silicate nanowires, interconnects and magnetic units in nanoelectronics.
Cobalt Silicide Nanostructures: Synthesis, Electron Transport, and Field Emission Properties
(2009-10-01)
Tsai, Chun-I
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Yeh, Ping-Hung
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Wang, Chiu-Yen
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Wu, Han-Wei
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Chen, Uei-Shin
Cobalt silicide nanostructures have been synthesized by a spontaneous chemical vapor transport and reaction method. The temperature and the vapor flow rate were shown to critically influence the growth of nanostructures. The effects of two main parameters on the growth of nanostructures were discussed. The phases formed were determined by the Gibbs free energy changes in the reactions. Various phases (CoSi, Co(2)Si) and morphologies, such as single-stern nanowires, three-dimensional (3D) nanowire networks, and aloelike nanostructures, have been synthesized. Very low turn-on field (1.42 V/mu m) and good conductance obtained from field-emission and electrical property measurements, respectively, indicate that CoSi nanowires are potentially useful for electronic devices.
Controlled growth of the silicide nanostructures on Si bicrystal nanotemplate at a precision of a few nanometres
(2011)
Hsin, Cheng-Lun
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Wu, Wen-Wei
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Chu, Li-Wei
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Hsu, Hung-Chang
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Chen, Lih-Juann
A nanotemplate of Si bicrystal was fabricated by wafer bonding. The surface electronic energy arrangement on the surface of the Si bicrystal has been measured by scanning tunneling microscopy. The stress effect on the stepped growth of titanium silicide nanorods on Si bicrystal was observed in an ultrahigh vacuum transmission electron microscope in real time. The growth behavior of the nanorods was found to be affected by the underlying dislocation arrays significantly. For a dislocation interspacing of 3.1 nm, the dislocation arrays confined the shape of the nanoclusters and nanorods. Compared to the time of the nanorod remaining at the same length, the elongating time is more than two orders of magnitude shorter. The stepped growth behavior is attributed to the stress contour of the surface strain induced by the underlying dislocation network. This study is constructive to the basic understanding of the stress effect on the initial stage of the reaction of metals on Si and the observation may be applied to nanostructure growth for future applications and design.
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.
Core-Shell Pd9Ru@Pt on Functionalized Graphene for Methanol Electrooxidation
(2018-01-01)
Kuo, Chih-Chia
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Chou, Shih-Cheng
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Chang, Yu-Chen
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Hsieh, Yi-Chieh
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Wu, Pu-Wei
A simple but effective electrochemical route to functionalize graphene is demonstrated. Cyclic voltammetric sweeps (CV) are performed in a 0.5 M H2SO4 aqueous solution on electrodes consisting of carbon cloth, graphene, and Nafion ionomer. Upon exposure to ambient oxygen, the formation of hydroxyl radicals from the oxygen reduction reaction during the CV cycles initiates the decomposition of the Nafion ionomer, which produces oxygenated functional groups on the graphene surface. Using contact angle measurements and X-ray photoelectron spectroscopy, various amounts of Nafion ionomer are explored to determine the optimum conditions for graphene functionalization. Afterwards, Pd9Ru nanoparticles with an average size of 3-4 nm are synthesized and impregnated on functionalized graphene (FGN). To prepare core-shell electrocatalysts, Pd9Ru/FGN is subjected to Cu underpotential deposition followed by a galvanic displacement reaction to deposit a Pt monolayer on the Pd9Ru surface (Pd9Ru@Pt). The assynthesized sample (Pd9Ru@Pt/FGN) exhibits enhanced performance in methanol electrooxidation, which includes abetter activity and lower susceptibility to poisoning by intermediates. The electrochemically active surface area (ECSA) of Pd9Ru@Pt/FGN shows a value that is 1.5-fold larger than that of Pd9Ru@Pt on untreated graphene (Pd9Ru@Pt/GN). In the durability tests, Pd9Ru@Pt/FGN and Pd9Ru@Pt/GN demonstrate losses in the ECSA of 14.9% and 30.3%, respectively. (C) 2018 The Electrochemical Society.
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
;
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.