Abstract
In this paper, the high quality single-walled carbon nanotubes (SWNTs) were synthesized by multilayered metal catalysts on silicon or silicon oxide substrate in thermal chemical vapor deposition of methane. The roles of multilayered metal catalyst were investigated by systematically varying the combination of multilayered structure. The scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and micro-Raman spectroscopy were used for characterization. It was found that aluminum supporting layer was very crucial in synthesizing high-purity SWNTs. A thin molybdenum layer in collaboration with an ultra-thin iron catalyst was found very effective in extending the operation window of SWNTs synthesis. The investigation of radial breathing mode (RBM) and the G-band/D-band intensities by micro-Raman measurements would further reveal the strong dependence of the diameter distribution of SWNTs on the different combinations of multilayered structure. An optimized combination was found Mo(0.2 nm)/Fe(1 nm)/ Al(10 nm) on silicon substrate, in which the peak of RBM was sharp and IG/ID ratio was at least 20 from micro-Raman analysis. Furthermore, the Auger electron spectrometer (AES) analysis was utilized to examine the evolution of the depth profile of multilayered structure due to the pre-treatment, which would lead to the examination of the role of each layer. The result of these investigations would be presented and discussed.