Browsing by Author "Chen, Chia-Fu"

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A novel method for fabrication of self-aligned double microlens arrays
(2007-04-15)
Ho, Jeng-Rong
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Shih, Teng-Kai
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Cheng, J. W. John
;
Sung, Cheng-Kuo
;
Chen, Chia-Fu
Based on the excimer laser microdrilling and the spin coating scheme, a new fabrication method of polymeric, double microlens arrays on a thin plastic pedestal sheet is proposed in this study. On each through hole on the pedestal sheet, a double microlens pair, consisting of two microlenses with different parabolic surfaces, is sited. The two microlenses of each pair are located respectively on both ends of the through hole and arranged surface to surface and automatically share a common lens principal axis. The fabricated microlens arrays are made of PMMA that are formed on a PMMA pedestal sheet with thickness of 100 mu m. The diameter and height for the microlens on one layer are of 150 mu m and 28 mu m, respectively, and they are correspondingly of 130 mu m and 24 mu m on the other layer. Experimental results demonstrate that the double microlens arrays have a better focusing property than the single-layer mircolens array. Simulation results indicate that, simply by changing the thickness of the pedestal sheet, the present fabricated double microlens arrays can serve the purposes for light collimating and diffusing. Due to its inherent simplicity in fabrication, the present method has high flexibility for making double microlens arrays with different lens configurations and various lens refractive indices. The facts that precise alignment and all processing steps are performed in ambient and at low temperature render the proposed approach a potential low-cost method for fabrication of double microlens arrays. (c) 2006 Elsevier B.V. All rights reserved.
Amorphous carbon coated silicon nanotips fabricated by MPCVD using anodic aluminum oxide as the template
(2007)
Chen, Te-Ming
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Pan, Fu-Ming
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Hung, Jui-Yi
;
Chang, L.
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Wu, Shich-Chuan
We have used nanoporous anodic aluminum oxide (AAO) as a template to fabricate amorphous carbon (alpha-C) coated silicon nanotips by microwave plasma chemical vapor deposition (MPCVD). During the preparation of the well-ordered AAO pore channel array, an underlying TiN layer was anodically oxidized as well in the late stage of the AAO anodization, forming titanium oxide nanomasks for Si nanotip fabrication. The titanium oxide nanomasks were then used to transfer the arrangement pattern of the AAO pore channel array to the Si substrate by plasma etch in the MPCVD system and, therefore, a well-ordered Si nanotip array was produced. An alpha-C layer similar to 5 nm thick was in situ deposited on the Si nanotips during the MPCVD process. The alpha-C layer was rich in nanocrystalline graphitic carbons according to Raman and Auger electron spectroscopies. The nanocrystalline graphitic carbons in the coating and the sharp tip shape made the Si nanotip a good field emitter and a field enhancement factor of similar to 659 was obtained. (c) 2007 The Electrochemical Society.
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
;
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.
Cation-mediated effects on zinc oxide films formed by chemical bath deposition
(2007-07-01)
Cheng, Hua-Chi
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Chen, Chia-Fu
;
Tsay, Chien-Yie
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材料科學與工程學系
;
Department of Materials Science and Engineering
Crvstalline ZnO films with a densely packed morphology were grown on a silicon oxide (SiOx) glass substrate by chemical bash deposition (CBD) in an aqueous-solution bath containing magnesium nitrate [Mg(NO3)(2)center dot 2H(2)O] used as a cation-mediation compound. zinc nitrate [Zn(NO3)2 center dot 6H(2)O], and dimethylarnineborane (DMAB) at 65 degrees C. Grains of ZnO films grown in nonmediated solution preferentially grew on the (002) plane. In the cation-mediated-solution bath, the films were compressed into a compact morphology by the increased tendency for films to grow in the (002) prefer orientation. The crystalline ZnO film exhibits good optical transmittance of over 90%. Additionally, the direct band-gap value was 3.22 eV, which is less than 3.38 eV, which was obtained using a nonmediated-solution bath. This was due to the lattice constant variation caused by cation mediation.
Characterization of HF-PECVD a-Si:H thin film solar cells by using OES studies
(2011-01-01)
Lien, Shui-Yang
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Chang, Yin-Yu
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Cho, Yun-Shao
;
Wang, Jui-Hao
;
Weng, Ko-Wei
Hydrogenated amorphous silicon (a-Si:H) films show considerable potential for the fabrication of thin film solar cells. In this study, the a-Si:H thin films have been deposited in a parallel-plate radio frequency (RF) plasma reactor fed with pure SiH(4). The plasma diagnostics were performed simultaneously during the a-Si:H solar cell deposition process using an optical emission spectrometer (OES) in order to study their correlations with growth rate and microstructure of the films. During the deposition, the emitting species (SiH*, Si*, H*) was analyzed. The effect of RF power on the emission intensities of excited SiH, Si and H on the film growth rate has been investigated. The OES analysis revealed a chemisorption-based deposition model of the growth mechanism. Finally, the a-Si:H thin film solar cell with an efficiency of 7.6% has been obtained. (C) 2010 Elsevier B.V. All rights reserved.
Deposition of Carbon Nanowall Flowers on Two-Dimensional Sheet for Electrochemical Capacitor Application
(2009)
Hung, Tsung-Chi
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Chen, Chia-Fu
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Whang, Wha-Tzong
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材料科學與工程學系
;
Department of Materials Science and Engineering
We have used bias-assisted microwave plasma chemical vapor deposition to synthesize (i) two-dimensional carbon nanowalls [(2D CNWs), monolayer] and (ii) three-dimensional carbon nanowalls [(3D CNWs), double-layer] on carbon cloth in a CH(4)/CO(2) system. The specific surface area of the 3D CNW electrode (1580 m(2)/g) was considerably larger than that of the 2D CNW electrode (364 m(2)/g). This higher surface area and more porous structure of the 3D CNW electrode resulted in its capacitance reaching as high as ca. 198 F/g at a scan rate of 10 mV/s. Electrochemical measurements suggested that this 3D electrode is a promising material for application in electrical storage devices.
Electron field emission from well-aligned GaP nanotips
(2010-11-01)
Lo, Hung-Chun
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Tsai, Jeff T. H.
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leu, Jih-Perng
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Chen, Chia-Fu
;
材料科學與工程學系
Field emission of electrons from single crystal gallium phosphide (GaP) nanotips has been investigated. GaP nanotip arrays were fabricated using silane-methane-argon-hydrogen based plasma using the self-masking dry etching technique in an electron-cyclotron-resonance microwave plasma enhanced chemical vapor deposition system. These nanotips have an average of 2 and 80 nm in apex and bottom diameters, respectively. They are 900 nm in height, which makes them the perfect electron emission source for their high aspect ratio topography. A nanosized silicon carbide (SiC) cap on each GaP nanotip in the array has been found. The SiC core has a heterointerface with GaP crystal that was observed using a high resolution transmission electron microscope. Field emission analysis shows low turn-on fields of 8.5-9 V/mu m. Cold electron emissions in Fowler-Nordheim type current-voltage were observed from such GaP nanotip arrays. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3506089]
Fabrication and carbon monoxide sensing characteristics of mesostructured carbon gas sensors
(2009-12-04)
Liu, Chueh-Yang
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Chen, Chia-Fu
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Leu, Jih-Perng
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Lu, Chih-Cheng
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Liao, Kuan-Hsun
We demonstrated a micro-chemoresistive gas sensing device using mesoporous carbon as the sensitive film and immobilized by dielectrophoresis (DEP) process. The mesoporous materials were characterized by X-ray diffraction (XRD) patterns, N(2) adsorption-desorption isotherms, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). N(2) adsorption-desorption isotherms shows the specific surface area of 1200 m(2)/g, total pore volume is 1.2 cm(3)/g of the mesoporous carbon, and the pore size distribution of mesoporous carbon yields an average pore size of 3 nm. SEM images show a rod-like morphology and TEM images show a highly ordered pore channel with linear arrays. CO gas sensor properties were measured and the resulting sensitivities were 5.7, 6.8, 8.8, 11.6, and 37.6% for concentrations of 30, 45, 60, 75, and 90 ppm. respectively. Additionally, this sensor also exhibited high sensitivity and fast response times for CO gas. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
Fabrication and CO Sensing Properties of Mesostructured ZnO Gas Sensors
(2009)
Liu, Chueh-Yang
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Chen, Chia-Fu
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Leu, Jih-Perng
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材料科學與工程學系
;
Department of Materials Science and Engineering
This study presents the synthesis of mesostructured ZnO using a template replication method and the fabrication of a carbon monoxide sensor using the synthesized ZnO using the dielectrophoresis process. The mesoporous carbon, CMK-3, was employed for the template and zinc nitrite was used as the precursor for synthesizing the ordered porous ZnO. The mesostructured ZnO was analyzed using X-ray diffraction (XRD) patterns, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and N(2) adsorption-desorption isotherms. The XRD patterns indicated that the ZnO exhibited a highly ordered structure after the template was removed. The morphology of the ZnO was randomly oriented and the structure was polycrystalline. The surface area, pore volume, and pore size of the porous ZnO were 61.3 m(2) g(-1), 0.31 cm(3) g(-1), and 5.3 nm, respectively. When CO gas was injected, the optimum sensitivities at 250 degrees C were 12.1, 14.6, 18.4, 26.0, and 60% when the CO concentrations were 10, 20, 30, 50, and 70 ppm, respectively.
Fabrication of Mesostructured Cobalt Oxide Sensor and Its Application for CO Detector
(2009)
Liu, Chueh-Yang
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Chen, Chia-Fu
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Leu, Jih-Perng
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材料科學與工程學系
;
Department of Materials Science and Engineering
The paper presents a method for mesostructured cobalt oxide sensor fabrication by the template replication method and immobilization using dielectrophoresis process. The method consists of enriching the mesostructured cobalt oxide particles in a microelectrode gap that drove mesostructured cobalt oxide particles to a high electric field region and then exposed to CO gas. The cobalt oxide sensor has improved sensing performance in carbon monoxide (CO) detection at concentration as low as 10 ppm and a very short recovering time, due to the higher surface area.
Fabrication of optical gratings by shrinkage of a rubber material
(2008-06-30)
Shih, Teng-Kai
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Ho, Jeng-Rong
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Liao, Hung-Yu
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Chen, Chia-Fu
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Liu, Chueh-Yang
Ordered wavy surface structures generated by deposition of a metal thin film on a pre-stretched PDMS plate were fabricated and its potential application for optical gratings was proposed. The orientation of the generated structures was always perpendicular to the pre-stretched direction and the pitch of the structure could be adjusted ranging from 4.5 mu m to 6.8 mu m by controlling the strength of the pre-stretched strain and the thickness of the surface metal film. Based on these periodic structures, various optical gratings were demonstrated. With a slight modification of the fabrication scheme, gratings with different orientations can be fabricated on both sides of the PDMS plate, the double-sided gratings, could be fabricated. It is believed the current method has the potential for the fabrication of a large-scale diffractive grating at lower costs. (C) 2007 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 PDMS (polydimethylsiloxane) microlens and diffuser using replica molding
(2006-11-01)
Shih, Teng-Kai
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Chen, Chia-Fu
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Ho, Jeng-Rong
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Chuang, Fang-Tzu
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材料科學與工程學系
This paper reports the fabrication method of PDMS (polydimethylsiloxane) microlens array based on the replica molding process, casting a liquid PDMS into concave microlens molds. Concave microlens molds were fabricated through spin-coating processes suspended a liquid PMMA film on the micro-drilled hole, leading to the formation of the special curvature. Then, PDMS microlens arrays and diffusers were fabricated by replica molding and discussed in this study. The fabricated microlenses have both good surface roughness and high-quality optical properties. Therefore, diffusers were fabricated by two-step replica molding. A high-intensity He-Ne laser beam was uniformly spread through diffusers. Experimental tests demonstrated that all PDMS elements are successfully fabricated by replica molding process and operated during optical measurement. (c) 2006 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.
High oriented ZnO films by sol-gel and chemical bath deposition combination method
(2009-05-05)
Cheng, Hua-Chi
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Chen, Chia-Fu
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Tsay, Chien-Yie
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Leu, Jih-Perng
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材料科學與工程學系
Poly-crystalline ZnO films with high oriented columnar grains were deposited on ZnO-coated seed layers by chemical bath deposition (CBD) in an aqueous-solution bath containing zinc nitrate [Zn(NO(3))(2)center dot 6H(2)O], and dimethylamineborane (DMAB) at 60 degrees C without pre-activation especially. Sol-gel ZnO films on glass substrates were used as the seed layers which the mean size of the crystals in seed layer increased from several to approximately 80nm at temperature from 150 degrees C to 550 degrees C. The deposited ZnO films on the ZnO-coated seed surfaces are preferentially on the (0 0 2) plane and exhibit increased from several 10 nm to 150 nm with increasing seed layer grain size. (C) 2008 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.
Iron oxide nanoparticles within the pore system of mesoporous SBA-15 in different acidity: the synthesis and characterization
(2007-07-01)
Liu, Chueh-Yang
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Chen, Chia-Fu
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Leu, Jih-Peng
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Lin, Yi-Chun
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材料科學與工程學系
Direct hydrothermal method is employed for incorporating iron into the pore structure of SBA-15. The resultant materials were analyzed by X-ray diffraction (XRD) patterns, N-2 sorption isotherm and X-ray photoelectron spectroscopy (XPS). The characterizations of XRD patterns and XPS revealed that iron nanoparticles were present as highly dispersed nanoclusters in the well-ordered mesoporous channels of SBA-15. The characterizations of t-plot reveal only microporous channels of SBA-15 are confirmed to be filled with iron nanoparticles, leaving the mesopores unaffected. The supported material still maintained its ordered mesoporous structure similar to SBA-15 and possessed high surface area, large pore volume and uniform pore size.
Label free sub-picomole level DNA detection with Ag nanoparticle decorated Au nanotip arrays as surface enhanced Raman spectroscopy platform
(2011-01-15)
Lo, Hung-Chun
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Hsiung, Hsin-I
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Chattopadhyay, Surojit
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Han, Hsieh-Cheng
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Chen, Chia-Fu
Label free optical sensing of adenine and thymine oligonucleotides has been achieved at the sub-picomole level using self assembled silver nanoparticles (AgNPs) decorated gold nanotip (AuNT) arrays. The platform consisting of the AuNTs not only aids in efficient bio-immobilization, but also packs AgNPs in a three dimensional high surface area workspace, assisting in surface enhanced Raman scattering (SERS). The use of sub-10 nm AgNPs with optimum inter-particle distance ensures amplification of the chemically specific Raman signals of the adsorbed adenine, thymine, cytosine and guanine molecules in SERS experiments. High temporal stability of the Raman signals ensured reliable and repeatable DNA detection even after three weeks of ambient desk-top conservation. This facile architecture, being three dimensional and non-lithographic, differs from conventional SERS platforms. (C) 2010 Elsevier B.V. All rights reserved.
Large-Grain Polycrystalline Silicon Solar Cell on Epitaxial Thickening of AIC Seed Layer by Hot Wire CVD
(2010-01-01)
Wang, Jui-Hao
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Lien, Shui-Yang
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Chen, Chia-Fu
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Whang, Wha-Tzong
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材料科學與工程學系
Large-grain polycrystalline silicon (poly-Si) films were prepared on foreign substrates by the epitaxial thickening of seed layers. The seed layers were formed by aluminum-induced crystallization (AIC). Large-grain n-i-p poly-Si solar cells were deposited on epitaxial seeds by hot-wire chemical vapor deposition (HWCVD). Highly (93%) crystalline fractions with a lateral grain size of 5 mu m and an intrinsic layer were grown without incubation. These techniques were employed to prepare large-grain poly-Si thin-film solar cells. An ITO/n-i-p (HWCVD)/p+ (AIC)/Ti/glass-structured poly-Si thin-film solar cell with an initial efficiency of 5.6% was obtained.
Low-temperature CVD growth of carbon nanotubes for field emission application
(2007-03-01)
Chen, Kuang-Chung
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Chen, Chia-Fu
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Lee, Jen-Hao
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Wu, Tai-Lin
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Hwang, Chian-Liang
For field emission application, carbon nanotube emitters were synthesized on catalyst-mixed thick-film electrode lower than 500 degrees C by chemical vapor deposition (CVD) method. Mixtures of Ni/tetraethyl silicate (TEOS) and conducting Ag powders were applied to fabricate the electrode by screen-printing processes. These processes are simple, low cost and easy to scale up for large sized panels. The field emission properties performed uniform emission image and high brightness (no less than 500 nits). The turn-on electric field was about 3.85 V/mu m with an emission current destiny of 10 mu A/cm(2), and the achieved current density was 1 mA/cm(2) driven by 5 V/mu m. (c) 2006 Elsevier B.V. All rights reserved.