Abstract Submitted to the    NANOTUBE'04 Conference:

For future applications of double-walled carbon nanotubes (DWNTs) in nanoscale electronics, their aligned long ropes with narrow diameter distributions were selectively synthesized by sulfur-assisted floating catalytic decomposition of methane in the presence of Fe catalyst with the addition of hydrogen. Resonant Raman measurements show that the outer and inner tubes are mostly semiconducting and metallic, with the corresponding diameter in the range of 1.7-2.0 nm and 1.0-1.3 nm, respectively. These special DWNTs with a dominant semiconducting and metallic combination can be expected to have promising applications as molecular cables. Comparing the SWNT bundles with similar outer diameters, about 3% Raman upshifts were obtained in their RBM region. Polarization Raman studies were performed on the aligned DWNT bundles and the results indicated that in addition to the RBM, the G-band, D-band and G'-band profiles all can be well deconvolved into two intrinsic independent single- walled carbon nanotube (SWNT) components constituting a DWNT. According to the G-band mode symmetry assignment results, the diameters and transport properties were obtained, which are in good agreement with those from RBM analysis. All these observations indicate that DWNTs possess unique characteristic Raman spectra different from other sp2 carbon materials.