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Formation of carbon cluster on the surface of diamond films for improving electron field emission properties
(2002-10-01)
Chang, YC
;
Tu, JC
;
Kuo, CT
;
Wang, CY
;
Lin, IN
The electron field emission properties of the diamond films were significantly improved via the formation of nanosized carbon clusters on their surface. The microstructures and Raman spectroscopy are markedly altered when the diamond films were coated with a thin layer of Fe/Co films (< 10 nm) and then post-annealed at high enough temperature ( > 800degreesC). The turn-on field was decreased from 14.8 to 7.6 V/mum and the electron field emission current density was increased more than 2 order of magnitude, from 20 to 2400 muA/cm(2), due to post-annealing process. (C) 2002 Elsevier Science B.V. All rights reserved.
Feasibility studies of magnetic particle-embedded carbon nanotubes for perpendicular recording media
(2003-03-01)
Kuo, CT
;
Lin, CH
;
Lo, AY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Nano-sized magnetic particles were successfully used as the catalysts to synthesize magnetic metal-encapsulated carbon nanotubes (CNTs) or nanoparticles on Si wafers in a microwave plasma electron cyclotron resonance chemical vapor deposition (ECR-CVD) system with CH4 and/or H-2 as source gases. The magnetic catalyst materials, including Fe-Pt, Co-Pt, Nd2Fe14B, Fe and Fe-Ni, were first deposited on Si wafers by a physical vapor deposition (PVD) method, with subsequent plasma treatment for nanoparticle transformation. The main process parameters include catalyst materials, hydrogen plasma catalyst pretreatment and deposition temperature. For applications in magnetic media, the process has the following advantages: perpendicularly aligned CNTs or nanoparticles; tip-growth CNTs; well-distributed magnetic particles; detectable magnetic field in each particle; high tube number density (up to 134 Gtubes/inch(2) for Fe-assisted CNTs); favorable catalyst size; higher shape and induced anisotropy; and nanostructures that can be manipulated. The catalyst particle sizes of Fe, Nb2Fe14B and Fe-Pt (35-40 mn in diameter) are uniform and greater than but close to the critical optimum size or single domain size, which favor a higher coercive force. The greatest coercive force can reach 750 Oe for Fe-assisted CNTs at a deposition temperature of 715 degreesC, which is comparable with values reported in the literature. The coercive force difference between the vertical and horizontal directions can reach 300 Oe for Fe-assisted CNTs, and 355 Oe for Nb2Fe14B-assisted CNTs. (C) 2002 Elsevier Science B.V. All rights reserved.
Comparisons on properties and growth mechanisms of carbon nanotubes fabricated by high-pressure and low-pressure plasma-enhanced chemical vapor deposition
(2004-11-01)
Lin, CH
;
Lee, SH
;
Hsu, CM
;
Kuo, CT
;
材料科學與工程學系
Effects of plasma pressure and the presence of nitrogen on growth of carbon nanotubes (CNTs) and their properties were studied by using microwave plasma chemical vapor deposition (MPCVD) (pressure=600-3300 Pa) and electron cyclotron resonance chemical vapor deposition (ECR-CVD) (pressure=0.3-0.6 Pa) systems. CH4/H-2 and CH4/N-2 were used as source gases, and Co as the catalyst. The structures and properties of CNTs were characterized by using field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectra, and field emission I-V measurements. The results show that. CNTs made by higher plasma pressure system have a higher growth rate (typically 1-3 mum/min), smaller tube diameter, better field emission properties, and better tube quality. The growth rate is related to the availability of carbon source. The morphology change from spaghetti-like to well-aligned CNTs is discussed in terms of directed ions. The change in field emission properties is reasoned in terms of geometric enhancement factor and screening effect for different tube morphologies. The presence of nitrogen plasma can have the following effects: increasing tube diameter, increasing straightness of CNTs, forming of bamboo-like CNTs, deterioration of field emission properties, and shifting of Raman peak toward lower-frequency side (or increasing residual tensile stress). (C) 2004 Elsevier B.V. All rigths reserved.
Tube number density control of carbon nanotubes on anodic aluminum oxide template
(2005-03-01)
Chen, PL
;
Chang, JK
;
Pan, FM
;
Kuo, CT
;
材料科學與工程學系
We demonstrate that the tube number density of well-aligned carbon nanotubes (CNTs) grown over the nanoporous anodic aluminum oxide (AAO) template can be directly controlled by adjusting the CH4/H-2 feed ratio during the CNT growth in a microwave plasma electron cyclotron resonance chemical vapor deposition (ECR-CVD) system. During the CNT growth, the nanotube growth and the amorphous carbon deposition on the AAO pore wall take place simultaneously. The amorphous carbon sediment will gradually cover up the AAO nanopores and prevent the nanotubes to grow out of the nanopores. By adjusting the CH4/H(2)feed ratio, one can control the amount of the deposited amorphous carbon and thus the number of CNTs grown over the AAO nanopores. It was found that the CNT density decreases linearly with increasing the CH4 concentration. The CNT density decreased by a factor of about 4.5 when the CH4 concentration increased from 9% to 91%. (c) 2004 Elsevier B.V. All rights reserved.

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