Generation and STM studies of carbon nanotubes and nanocones

Abstract

Novel forms of carbon have attracted intense interest since the discovery of C60, a molecule with a spherical cage, and its solid form. In this dissertation, our research work on the generation and scanning tunneling microscopy (STM) studies of two novel carbon structures, tubules and cones are summarized. We have produced nanotubes of carbon on a highly-oriented pyrolytic graphite substrate by vapor-phase growth. Using a scanning tunneling microscope, we found tubules with extremely small diameters from 1 nm to 8 nm. Their lengths are up to several hundred nanometers. They are closed by hemispherical caps. Some of them are isolated while some are parallel aligned and closely packed, forming bundles. Atomic resolution images of carbon tubules were obtained for the first time, showing that the tube surfaces are perfect graphitic networks. Besides tubular structures, we also produced nanocones of carbon by the same generation method as that of tubules. This is the first observation of carbon conical structures. The observed cones are up to 24 nm in length and 8 nm in base diameter. Amazingly they all have a unique cone angle of ~19°. We show that this is the smallest one among five possible opening angles for perfect graphitic cones. Based on our STM observation, we propose that the growth of carbon nanotubes, nanocones, and fullerenes may all be initiated by fullerene-type nucleation seeds. The number and the distribution of pentagons may play an important rule in their growth process.