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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
;
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.
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
;
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.
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
;
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 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
;
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.
Quantitative limitation of active site and characteristics of chemical oxidized well-aligned carbon nanotubes
(2008-06-30)
Hung, Tsung-Chi
;
Chen, Chia-Fu
;
Chen, Mi
;
Chen, Chien-Chung
;
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.
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
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Wang, Jui-Hao
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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.
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.
One-step fabrication and field emission properties of petal-like carbon nanotubes
(2009-02-01)
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
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Department of Materials Science and Engineering
We have used bias-assisted microwave plasma chemical vapor deposition to synthesize (i) carbon nanotubes (CNTs) possessing a graphitic carbon nanoflake (CNF) morphology, (ii) CNF spheres, and (iii) a pure carbon nanoflake film (CNFF) on stainless-steel substrates. We employed CH(4) and CO(2) as the precursors to these carbon nanomaterials(CNMs); the use of CO(2) aided the destruction of the CNT surfaces and reduced the growth temperature range to 380-450 degrees C at 300 W, as a result of the presence of oxygen-based species in the plasma. Applying an external bias of - 150 V led to the growth of CNTs possessing specifically oriented graphitic CNFs. We used scanning electron microscopy and high-resolution transmission electron microscopy to observe the morphologies and graphitic structures of these CNMs. Field emission measurements of a CNT/CNF-coated electrode revealed that the turn-on field was ca. 2.73 V/mu m. (c) 2008 Elsevier B.V. All rights reserved.
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
;
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.
Fabrication of PDMS (polydimethylsiloxane) microlens and diffuser using replica molding
(2006-11-01)
Shih, Teng-Kai
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Chen, Chia-Fu
;
Ho, Jeng-Rong
;
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.

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