| Research Abstract |
Single-walled carbon nanotubes (SWNTs), due to their unique charilty-dependent electrical properties, extremely high thermal conductivity and high mechanical strength, are proposed for various applications ranging from optical, thermal, electrical devices to tips of scanning probe microscopes, high strength materials and conductive composite materials. For early realization of the applications, it would be beneficial to synthesize high-purity SWNTs on substrates. In the current project, by extending the alcohol catalytic CVD method previously developed in the group, we have developed a method to synthesize SWNTs on quartz and silicon substrates.
Until several years ago, carbon hydrates or carbon monoxide had been commonly used as carbon sources for SWNT syntheses. By using alcohol as the carbon source, we previously showed that it is possible to grow high purity SWNT at relatively low temperature. As it is beneficial to synthesize SWNTs directly on silicon or quartz substrates for therm
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al and optical device applications, in this project, we have established a dip-coating method, where Cobalt/Molybdenum acetate is coated on the substrate then thermally oxidized to form uniform-size catalytic nano-particles. With this dip-coating technique, we have succeeded in synthesizing a film of SWNTs aligned vertically with respect to the substrates.
Furthermore, by measuring the laser absorption during the CVD growth process, real time identification of the thickness of vertically aligned SWNT (VA-SWNT) films was realized. By quantifying the initial activity and lifetime of catalysts from the time histories of the film thickness at various experimental conditions, it was found that the growth process is governed by a first order chemical reaction. In addition, we have discussed the growth mechanisms by studying the experimental results together with the molecular dynamics simulations of the growth process. With the knowledge learnt in the above studies, experimental conditions of the alcohol catalytic CVD process were optimized and, as a result, stable and repeatable syntheses of over 20 micrometer thick VA-SWNT films have been realized.
Finally, Raman spectra and UV/1R optical absorption spectra of VA-SWNT films were measured. A method to check the alignment of the SWNT film was established by identifying a radial breathing mode that is unique to VA-SWNT film with polarized Raman spectroscopy. Unique polarized optical absorption characteristics of SWNTs were also clarified. Less
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