Chapter 4 - Structure of Multi-Walled and Single-Walled Carbon Nanotubes. EELS Study

Abstract

This chapter reviews several structural characterizations of carbon nanotubes (CNTs) with the cylindrical graphite from the viewpoint of transmission electron microscopy (TEM). Especially, electron energy loss spectroscopy (EELS) by using an energy-filtered TEM is applied to reveal the dependence of fine structure of EELS on the diameter and the anisotropic features of CNTs. Although CNTs showed similar EELS pattern in plasmon-loss and core-loss regions to graphite, SWCNT and fine MWCNT with a diameter less than 5 nm had different features. Furthermore, it has been found out that the angular dependent EELS along the direction normal to the longitudinal axis of CNT shows stronger contribution from π electrons than a electrons. It has been confirmed that the anisotropy of CNT exists in the structure and electronic property. Although it is scarcely able to obtain a lattice image of the graphitic structure from a single-walled CNT (SWCNT), whole the CNT should be aligned normal to the incident electrons without any inclination and bending. Therefore, it is difficult to detect the helicity in a CNT from the images. Some investigations have been devoted to the structures at the end and around the bends of CNTs. There could be the presence of pentagons or heptagons, but it is also not easy to distinguish the individual polygons by TEM.