Single-walled carbon nanotubes (SWNTs) have one dimensional structure with a nanoscale and thus provide a good opportunity for not only theoretical exploration but also practical applications such as nanoelectronics. However, despite the great deal of studies during the past decade, control of the conductivity of SWNTs is still difficult because the character is changed by chirality or diameter. Thus, chirality or diameter control of SWNTs is recognized as a critical and urgent issue to overcome. The most common approach to date is control of the catalyst size using electron beam (EB) lithography or solution-based catalytic nanoparticles.
Here, we present controlled synthesis of SWNTs on various structured substrates to facilitate direct characterization of as-grown tubes. For high controllability of the growth process, we used thermal chemical vapor deposition with methane and hydrogen gases. EB-patterned thin film catalyst and ferritin-derived nanoparticles were used and compared as catalysts. Sizes of catalysts and grown SWNTs were estimated from atomic force microscopy results. In addition to the plane substrates, multi-dimensional patterned substrates were fabricated for suspended SWNTs growth, which give intrinsic mechanical, electrical, and optical properties. We obtained significantly enhanced optical properties from the individual suspended SWNT, which may help to develop diameter- and chirality-control. We also grew SWNTs on silicon nitride membranes to investigate the size relationship between catalyst and resultant nanotube by direct observation with transmission electron microscopy. Our results will be developed towards SWNTs' diameter control by optimizing the combination of controlled growth and characterization.
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