SEM and Raman spectroscopy of multiwalled carbon nanotubes grown by novel technique of ash supported catalysts

Multiwalled carbon nanotubes (MWCNTs) were grown on a novel ASC catalyst and on catalyst deposited by SCC method on silicon wafer, by thermal CVD of acetylene. Fe and Ni were used as catalyst for ASC. Samples were analyzed by SEM and Raman spectroscopy. SEM analysis shows that CNTs grown on ASC have narrower diameter distribution (64 +/- 6 nm) compared to CNTs grown on SCC (67 +/- 10.5 nm). However, SEM and Raman spectroscopy studies show CNTs grown on SCC are of better quality. The same samples were studied after standard purification procedure of oxidation after annealing at high temperatures. SEM and Raman spectroscopy show that overall quality of ensemble of CNTs has improved. After annealing, diameter decreases for larger diameter similar to 200 nm nanotubes while it increases for CNTs of smaller diameter similar to 70 nm. To explain the increase in diameter of similar to 70 nm CNT's, a phenomenological model has been proposed. The results of Raman spectroscopy and SEM corroborate the proposed model.