Browsing by Author "Teng, IJ"

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Growth mechanism and properties of the well-aligned-carbon-coated Si nanocones by MPCVD
(2005-11-01)
Chuang, PK
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Teng, IJ
;
Wang, WH
;
Kuo, CT
;
材料科學與工程學系
in order to clarify the possibility to form Si nanocones under the same gas sources (CH4 and H,) and deposition system (microwave plasma chemical vapor deposition (MPCVD)), a process were successfully developed to synthesize the well-aligned amorphous carbon-coated Si nanocones (a:C-SNCs), and their growth mechanism is proposed. This process includes depositing 10 nm Co-catalyst on Si wafer by physical vapor deposition (PVD) and then followed by H-plasma pretreatment to form Co nanoparticles. The pretreated specimens were then used to synthesize various nanostructures under a higher negative Substrate bias. The deposited nanostructures and their compositions were characterized by SEM, HRTEM, ED, EDS and Raman spectroscopy. The results indicate that the most important parameters for forming a:C-SNCs include a lower CH4/H-2 ratio, a higher negative substrate bias and assistance of the carbon-soluble nano-sized catalysts, such as Co. Under a higher enough negative substrate bias (>= 240 V), the etching rates of the catalyst particles and the substrate by the positive species are greater than the carbon deposition rate; a:C-SNCs can be formed. We propose that the cone shape of the nanostructures is essentially resulted from a progressive reduction in catalyst particle sizes under the conditions of higher etching rate than deposition rate on the catalyst surfaces, which may be partially due to a reduction in the Co melting temperature by the presence of carbon in the Co matrix. This mechanism is supported by the facts that a:C-SNCs find no catalysts or very small catalysts on the tips; the catalyst sizes show no significant reduction in sizes after the same a:C-SNCs deposition conditions except no presence of carbon; the diameter of the cone base has no significant differences in size as the original catalyst size after H-plasma pretreatment. Our mechanism gives the guideline to form the nanocone structures by MPCVD with same gas sources (CH4 and H-2). (c) 2005 Published by Elsevier B.V.
Nanofabrication and the structure-property analyses of phase-change alloy-ended CNTs
(2006-02-24)
Wang, WH
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Chao, KM
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Teng, IJ
;
Kuo, CT
;
材料科學與工程學系
In order to cap the tip cavities of the open-ended carbon nanotubes (CNTs) with the phase-change alloy for potential applications as the nano-resolution storage media, the Co-assisted CNTs were first synthesized by electron cyclotron resonance chemical vapor deposition (ECR-CVD) with H-2 and CH4 as the gas sources. Then, the as-grown CNTs were post-treated in H-plasma atmosphere to remove the carbon layers covered on catalysts, and subsequently immersed in HNO3 solution to remove the catalysts from the tips. The open-ended CNTs with a bowl-like-shape tips were followed by coating with a phase-change alloy layer of GeSbTeSn via sputtering process, and then heat treated in vacuum for 30 min to trim the alloy off from the sidewalls of CNTs to obtain the alloy-ended CNTs. The structures and properties in each processing step were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and Auger electron spectroscopy (AES). The experimental results show that the well-oriented phase-change alloy-ended CNTs over a large area are fabricated successfully. Furthermore, the Auger analyses show the compositions of the phase-change alloys may be changed from Te-rich to Ge-rich after being capped on the tips of CNTs. (c) 2005 Elsevier B.V. All rights reserved.