Browsing by Author "Chen, Chien-Chung"

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Catalyst-free, low-temperature growth of high-surface area carbon nanoflakes on carbon cloth
(2009-01-01)
Hung, Tsung-Chi
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Chen, Chia-Fu
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Chen, Chien-Chung
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Whang, Wha-Tzong
;
材料科學與工程學系
We have used a microwave plasma-enhanced chemical vapor deposition system to synthesize two-dimensional (2D) and three-dimensional (3D) structures of carbon nanoflakes (CNFs). This catalyst-free, low-temperature synthesis involved introducing CO(2) and CH(4) as reactants at a specified ratio of 2:3. We obtained uniform 2D arrays of CNFs at lower microwave powers (200 or 300 W) and substrate temperatures (up to 420 degrees C); their thickness was close to 1 mm. At a microwave power of 400 W, we obtained a 3D architecture comprising the smallest nanoflakes reported to date. The specific surface area of the 3D structure was double that of the corresponding 2D arrays. We suspect that such structured carbon materials might have great potential for energy storage applications. (C) 2008 Elsevier B. V. All rights reserved.
Fabrication of optical reflectors by using of elastomer with self-organized undulations
(2008-08-01)
Wang, Jui-Hao
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Shih, Teng-Kai
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Chen, Chia-Fu
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Chen, Kuang-Chung
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Chen, Chien-Chung
Back-surface diffusive reflectors have been widely applied in many optical systems to promote the efficiency used in system. In this work, we propose a novel way to fabricate a soft diffusive reflector by using of silicone (polydimethylsiloxane, PDMS). High-reflectance substrates were first fabricated by mixing nanoscaled TiO2 powders with PDMS polymers, and then microscale wave-like undulations were spontaneously developed after the substrates were dipped into H2SO4/HNO3 solutions. After optical examination, a TiO2/PDMS plate comprising microscale undulations, which can surely serve as a reflector, could reflect and diffuse light effectively. Besides, all fabrication processes can be executed in the ambient environment and at low temperature. This proposed method has a potential for mass production in the future. (c) 2008 Elsevier B.V. All rights reserved.
Fabrication of soft reflective microoptical elements using a replication process
(2008-01-01)
Shih, Teng-Kai
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Ho, Jeng-Rong
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Wang, Jui-Hao
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Chen, Chia-Fu
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Liu, Chueh-Yang
This paper reports the fabricated method and optical performance of soft, reflective elements with nonspherical surface. Based on excimer laser microdrilling and spin coating processes, a PMMA film suspended on microdrilled holes was used as a concave mold. Then, a high-reflectance material, mixed PDMS rubber polymers with TiO2 nanoscale powders, was cast on the PMMA mold. Finally, both of concave and convex elements could be fabricated through soft replica molding processes and these elements could directly reflect light without the deposition of metal coatings. Therefore, we proposed a model regarding a flexible cable with its weight suspended on fixed points to explain the formation mechanism of PMMA molds. With the change of diameters of microholes and thicknesses of PMMA films, the suspended height of films was surely controllable. Therefore, the curvature radiuses and shapes of these aspherical elements also depended on the diameters of microholes and the thicknesses of PMMA films. Experimental results demonstrated that soft reflective elements have good surface qualities and high-quality optical properties. Besides, all fabrication steps can be executed in ambient environment and at low temperature, the proposed method has a potential for mass production. (C) 2007 Elsevier B.V. All rights reserved.
Improved Catalytic Performance of Pt Supported on Multi-Wall Carbon Nanotubes as Cathode for Direct Methanol Fuel Cell Applications Prepared by Dual-stepped Surface Thiolation Processes
(2009-12-01)
Chen, Tsan-Yao
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Lin, Tsang-Lang
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Chen, Chien-Chung
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Chen, Chieng-Ming
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Chen, Chia-Fu
This study develops a simple surface modification process for modifying the MWCNT surface by thiolation reaction after the conventional nitric acid treatment for strong interface attachment of Pt NPs and improved dispersion onto MWCNTs. The thiolated MWCNTs (Pt/MWCNTs) showed significant improvement of methanol electro-oxidation activity compared with that treated only by nitric acid solution. The prepared electrode with thiolated MWCNTs was used as the cathode for assembling MEA for DMFC single-cell applications. Testing results indicate that the thiolated MWCNT cathode can improve the power density of MEA by more than 300% (from 4.6 to 20.6 mW cm(-2)) compared with that treated only by conventional nitric acid reactions. The dual-step modification process for MWCNT surface treatment showed significant improvement over the convention nitric acid treatment and can be successfully used in DMFC applications.
Modification of multi-walled carbon nanotubes by microwave digestion method as electrocatalyst supports for direct methanol fuel cell applications
(2007-01-01)
Chen, Chien-Chung
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Chen, Chia-Fu
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Chen, Chieng-Ming
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Chuang, Fang-Tzu
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材料科學與工程學系
Multi-walled carbon nanotubes (MWCNTs) which were directly synthesized on carbon cloth were modified by a microwave digestion method in 5 M HNO3 for supporting Pt nanoparticles. The characterizations of modified CNTs were carried out by TEM, XPS, FTIR and Raman spectroscopy. The HRTEM image shows the caps of MWCNTs are opened after modifying by microwave digestion method. The open-end and undamaged MWCNTs can provide a larger surface area for supporting more catalysts. Furthermore, the methanol electrocatalytic oxidation of microwave digestion treated Pt/MWCNTs electrode shows higher current density than pristine and nitric acid-treated MWCNTs from cyclic voltammograms. This can be an effective and undamaged method for modifying CNTs. (c) 2006 Elsevier B.V. All rights reserved.
One-Step Fabrication of Carbon Nanotubes Decorated with Graphitic Nanoflakes for Energy Storage Systems
(2010-07-01)
Hung, Tsung-Chi
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Chen, Chia-Fu
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Chen, Chien-Chung
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Whang, Wha-Tzong
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材料科學與工程學系
We have used a bias-assisted microwave plasma chemical vapor deposition system to synthesize carbon nanotubes presenting graphitic nanoflakes, named coral-like carbon nanotubes, and well-aligned carbon nanotubes on carbon cloth substrates. Applying an external bias of -100 V led to the growth of well-aligned carbon nanotubes. In the absence of an external bias, the coral-like nanotubes presenting graphite nanoflakes were formed. The specific surface areas of the well-aligned and coral-like carbon nanotubes electrodes were 90.31 and 143.69 m(2)/g, respectively. In terms of energy storage, we estimated the capacitance of the coral-like carbon nanotube electrode to be ca. 194 F/g in an electrolyte of 1 M H(2)SO(4). This value is almost double that of the well-aligned carbon nanotubes electrode (104 F/g), presumably because the presence of the carbon nanoflakes had a positive influence on the migration and adsorption of ions within the electrode. The fitting results indicated that the coral-like carbon nanotubes electrode behaved as a traditional electrochemical capacitor. Durability tests revealed that the coral-like carbon nanotube electrode was reliable, with a decay of 9% in capacitance over 1000 cycles.
One-step fabrication of surface-relief diffusers by stress-induced undulations on elastomer
(2009-09-01)
Wang, Jui-Hao
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Chen, Chia-Fu
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Ho, Jeng-Rong
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Shih, Teng-Kai
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Chen, Chien-Chung
In this study, we demonstrated that microscale surface undulations induced by acid treatment could serve as the surface relief on diffusers coated with a layer of PDMS polymer. Since the orientation of undulations was found to be always disordered, these undulations would scatter light uniformly. The periodicity of the undulations could be adjusted by the control of duration of the dipping of the elastomer into H(2)SO(4)/HNO(3) solutions and by the volume ratio of H(2)SO(4)/HNO(3) the solution, resulting in the modulation of diffusing ability of diffusers. The optical properties, transmittance, and light diffusivity, were characterised. This proposed approach offers potential for mass production of surface-relief diffusers. In addition, the proposed method allows the creation of undulations on arbitrary substrates. (C) 2008 Elsevier Ltd. All rights reserved.
Optical diffusers based on silicone emulsions
(2009-12-01)
Wang, Jui-Hao
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Lien, Shui-Yang
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Ho, Jeng-Rong
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Shih, Teng-Kai
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Chen, Chia-Fu
The present study provides an experimental approach for fabricating optical diffuser films based on silicone emulsions. The silicone emulsion consisting of silicone polymer (Sylgard 184) and NaCl aq. solution was used as the optical material of diffusers, wherein NaCl aq. solution was severed as surfactant to stabilize the emulsions. After stirring mechanically, microscaled water drop with various sizes distributed randomly in silicone polymer, wherein water drop was used as scattering diffusion particles. To modulate the volume of NaCl aq. solution, the diffusing performance of diffusers could be change by different amount drop particles. Thereafter, an optical examination was carried out to characterize optical properties, transmittance. and light diffusivity of volumetric diffuser films. (C) 2009 Elsevier B.V. All rights reserved.
Quantitative limitation of active site and characteristics of chemical oxidized well-aligned carbon nanotubes
(2008-06-30)
Hung, Tsung-Chi
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Chen, Chia-Fu
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Chen, Mi
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Chen, Chien-Chung
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材料科學與工程學系
For many years, acid treatment processes have been used to modify substances for their applications on energy storage devices, such as electrochemical capacitors, fuel cells, etc. It is obvious that the increase of surface area and functional groups has beneficial influence on the amount of reactant adsorption. However, the quantitative limitation of active site has been poorly discussed until today. In this experiment, nitric acid (2 M and 14 M) was introduced at 90 degrees C over different periods of time to oxidate the well-aligned multi-wall carbon nanotubes (MWNTs), which were synthesized directly using carbon cloth (CC) as the substance. Quinoidal functional groups on active CNTs, such as -COOH and -OH, were found to be the result of chemical reaction. Pt catalyst, which was extracted from H2PtCl6 center dot 6H(2)O, was deposited onto the carbon nanotubes using electroless plating in chloroplatinic acid solution. The extent of Pt adsorption was measured and was substantially larger than the as-prepared CNTs. It was found that the state of quantitative limitation existed in both 2 M and 14 M systems. A model was also developed to illustrate the limitation in the active site due to the chemical oxidation. (C) 2007 Elsevier B.V. All rights reserved.
Relaxation and Executive Control Processes in Listeners: An Exploratory Study of Music-Induced Transient Suppression of Skin Conductance Responses
(2015-07-01)
Tsai, Chen-Gia
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Yang, Chien-Ming
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Chen, Chien-Chung
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Chen, I-Ping
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Liang, Keng-Cheng
As music unfolds over time, fluctuations in listeners\' arousal level can be assessed by physiological measures. Strong emotional feelings induced by music are usually accompanied by heightened physiological arousal as reflected by increased skin conductance responses (SCRs). The aim of this study was to demonstrate that SCRs can be suppressed by musical events; cognitive-emotional processing of music in the central nervous system may lead to decreases in sympathetic activity and transient inhibition of sweat gland innervation. We recruited nonmusicians and recorded their real-time SCRs during the presentation of musical excerpts. Among 48 musical excerpts, seven excerpts were found to transiently reduce SCR amplitude to a level below the resting control value. Music analysis revealed that anticipation of sudden accents, music-evoked feelings of tenderness, and habituation or cancellation of an alarm in listeners may be associated with significant antipeaks on the average curve of SCR amplitude. In light of the neural mechanisms underlying SCR regulation, we suggest that an antipeak of average SCR amplitude represents a physiological signature of transient relaxation or executive control. With regard to music cognition, our findings shed new light on the perception of musical-tension/relaxation contrasts, major-minor ambiguity, and musical repetitions.
The parametric study of carbon nanotips grown by MWPECVD with controllable sharpness using various metallic catalysts
(2006-11-01)
Chen, Chien-Chung
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Chen, Yi-Hui
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Chen, Chia-Fu
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材料科學與工程學系
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Department of Materials Science and Engineering
A parametric study for growing vertically aligned carbon nanotips utilizing microwave plasma enhanced chemical vapor deposition was presented. The effects of process parameters including process time, microwave power and applying bias were discussed. The height of nanotips was affected by the microwave power and process time. The growth of rod-shape or tip-shape structure depends on the microwave power. The high microwave power is favorable for growing rod-shape structure which results from the faster diffusion of carbon atoms in the metallic catalysts under high temperature. The sharpness of carbon nanotips seem possibly to be controlled by varying bias voltage. These carbon nanotips exhibit the characters of high number density and well vertical alignment. Furthermore, we demonstrated that the growth of carbon nanotips by different metallic catalysts, such as Au, Pt, Ag and Si, could be chosen for applying in various regions. (c) 2006 Elsevier B.V. All rights reserved.
Topographic control on silicone surface using chemical oxidization method
(2007-10-15)
Shih, Teng-Kai
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Ho, Jeng-Rong
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Chen, Chia-Fu
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Whang, Wha-Tzong
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Chen, Chien-Chung
The paper describes a wet process for modifying the surface of polydimethylsiloxane (PDMS) using H2SO4/HNO3 solutions. The oxidation on the surface of PDMS was confirmed by the examinations of Fourier transform infrared spectrometry (FTIR), contact angle of water drop and X-ray photoelectron spectroscopy (XPS). The hydrophobic surface of pristine PDMS was not only changed to hydrophilic, but also formed wrinkles on it after chemical modification. Bilayer systems, stiff oxidized PDMS layers were capped on soft PDMS foundations, would generate easily compressive stresses due to the large difference in volumetric contraction rates and led to form wrinkles on the surface. Experimental results demonstrated the periodicity of wrinkles was controllable by controlling the duration of oxidation. Therefore, wrinkles could be arranged orderly by the guidance of external forces before oxidization. The potential technology for generating and ordering wrinkles on the PDMS surface is valuable in the applications of pressure sensors, biology, micro-optics and nano-/micro-fabrication in the future. (C) 2007 Elsevier B.V. All rights reserved.