Abstract Submitted to the    NANOTUBE'04 Conference:

It has been widely reported that the single-walled nanotubes(SWNTs) tend to grow in bundles. Similar bundle-like growth of double-walled nanotubes(DWNTs) were also observed and characterized. However, the growth of bundles of the nanotubes with the thicker and well-identified layers is often regarded difficult due to their defects. In this work, we will show the experimental evidence of the existence of triple-walled nanotubes(TWNTs). Acetylene was decomposed on Fe/MgO catalysts at 950℃ with argon and hydrogen existence. The carbon deposition was characterized by HRTEM, SEM and Raman spectroscopy. Thickset TWNT bundles, with hundreds of nanometer in length and an aspect ratio of about three, were observed in the sample. The nanotubes in bundles have the almost same structural parameters, e.g. the inner and outer diameter of 0.4nm and 2.1nm respectively, the number of layers. The bundles have the plane base or tips, suggesting that the nanotubes grow from a certain facet as substrate. Basing on our experimental evidences, a mechanism of growth of nanotube bundles on Fe/MgO catalysts is proposed.