Browsing by Author "Liu, Chueh-Yang"

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Fabrication and carbon monoxide sensing characteristics of mesostructured carbon gas sensors
(2009-12-04)
Liu, Chueh-Yang
;
Chen, Chia-Fu
;
Leu, Jih-Perng
;
Lu, Chih-Cheng
;
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
;
Chen, Chia-Fu
;
Leu, Jih-Perng
;
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
;
Chen, Chia-Fu
;
Leu, Jih-Perng
;
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
;
Ho, Jeng-Rong
;
Liao, Hung-Yu
;
Chen, Chia-Fu
;
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 soft reflective microoptical elements using a replication process
(2008-01-01)
Shih, Teng-Kai
;
Ho, Jeng-Rong
;
Wang, Jui-Hao
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Chen, Chia-Fu
;
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.
Iron oxide nanoparticles within the pore system of mesoporous SBA-15 in different acidity: the synthesis and characterization
(2007-07-01)
Liu, Chueh-Yang
;
Chen, Chia-Fu
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Leu, Jih-Peng
;
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.
MESOPOROUS CARBON POWDER GAS SENSORS FOR DETECTION OF CARBON MONOXIDE
(2009-12-01)
Lu, Chih-Cheng
;
Liao, Kuan-Hsun
;
Tsai, Jeff Tsung-Hui
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Liu, Chueh-Yang
;
Leu, Jih-Perng
This article reports a new class of silicon-based microgas sensors utilizing hexagonally-ordered mesoporous carbon powders (MCPs) as the sensitive film. The mesoporous carbon powders featuring high-specific surface area are replicated by the SBA-15 silica template and immobilized between Cr electrodes on a 9 x 9 cm silicon chip by using a. c. dielectrophoresis (DEP) process at room temperature. The silicon sensor platform comprises Cr microheaters embedded in a dielectric thin membrane manufactured by microelectromechanical systems back-etching techniques. It is shown that MCPs can be satisfactorily aligned along electric fields and accumulated to the electrode area. Investigations into CO detection are carried out to verify gas-sensitive characteristics of the MCP nanofilm. Our experimental results disclose the mesoporous carbon powders are successfully chemoresistive to CO, and demonstrate distinct resistance change with respect to ppm-level variation. In addition, response time, recovery time, and reproducible sensing behavior are experimentally obtained.
Study of leading factors in formation of surface wavy structures on a rubber material
(2006-12-15)
Shih, Teng-Kai
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Chen, Chia-Fu
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Ho, Jeng-Rong
;
Liu, Chueh-Yang
;
Chuang, Fang-Tzu
Wavy structures are often observed on the surface of a rubber material (polydimethylsiloxane, PDMS) covered with a thin metallic film. In this study we demonstrate that the orientation, periodicity, location of formation, and range of periodicity of the wavy structures can be regulated by three leading factors including the surface pattern, substrate hardness and the thickness of the metallic film. Results show the orientation of the wavy structures can be adjusted by the location, shape and size of the surface patterns. Enhancement of the substrate hardness can prevent forming random wavy structures. The thickness of surface metallic film significantly influenced the periodicity of the structures. Experimental results revealed an increase of the thickness of surface Au film by 50 nm, the periodicity was increased roughly by 1 mu m. A compound structure, combining longitudinally preset patterns and transversely induced wavy structures, and a parallel wavy structure fabricated, respectively, by suitable arrangement of pattern configurations and adjustment of substrate hardness were demonstrated. The relatively simple approaches proposed here show the potential application in fabrication of designated complicate structures. (c) 2006 Elsevier B.V. All rights reserved.
Tunable interconnectivity of mesostructured cobalt oxide materials for sensing applications
(2009-04-02)
Liu, Chueh-Yang
;
Chen, Chia-Fu
;
Leu, Jih-Perng
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A mesostructured cobalt oxide microsensor was fabricated using a template replication method under different hydrothermal treatments, and attempts were made to enhance the response of this gas sensor. To evaluate the sensing performance, the sensing materials were deposited via the dielectrophoresis (DEP) process, on micro-hot-plate platforms with interdigitated electrodes. The resistance changed when the carbon monoxide target gas was injected at the optimum temperature. The mesostructured cobalt oxide material with high hydrothermal treatment revealed the well-ordered domains, whereas with low hydrothermal treatment it did not contain ordered domains. Moreover, the cobalt oxide high hydrothermal material had 1.5 times the response to 70 ppm carbon monoxide as the low hydrothermal treatment sample. The unobstructed interconnectivity promotes gas diffusion and increases the active surface areas. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.