Chapter 1: Literature Review on Carbon Nanotubes

Carbon Nanotubes (CNTs) are believed to be the ultimate nanomaterial, due to their exceptional thermal conductivity, electronic properties, and mechanical strength. Discovered by Iijima Sukumo, an electron microscopist from the NEC laboratory in Japan in 1991, they have been capturing the imagination of physicists as well as chemists for the last thirteen years. They are the fifth existing form of solid-state carbon; the four other forms have been: diamond, graphite, non-crystalline structures like charcoal, and fullerene. The discovery of CNTs is a direct consequence of the discovery of cage-like molecules named fullerenes (C60) that are solely composed of sixty carbon atoms arranged in pentagonal and hexagonal rings. Fullerenes were discovered in 1985 by Kroto et al. who synthesized very small amounts of C60 by laser vaporization of graphite in a helium atmosphere. Their discovery was closely followed by the work of Krätschmer et al. who synthesized larger amounts of C60 by carbon arc-discharge. Iijima subsequently discovered CNTs by studying with High-Resolution Transmission Electron Microscopy (HRTEM) the cylindrical deposit that was formed on the graphite cathode after arc-evaporation. CNTs can be viewed as wrapped sheets of graphene, closed at each end with half fullerene caps. They are a few nanometers wide, several micrometers long, and one atom in wall thickness. The CNTs’ formation comes from the energy lowering of the graphene sheets’ dangling bonds, leading to the rolling-up of the sheets. The bonding of carbon atoms in a CNT and a graphene sheet are very similar, and the sp hybridization structure of graphene is the major constituent of CNTs. Two types of CNTs possess a high structural perfection. Single-Walled CNTs (SWNTs) consist of a single graphene sheet wrapped in a cylindrical fashion (Figure 1.1). Multi-Walled CNTs (MWNTs) are composed of multiple graphene sheets concentrically rolled-up. SWNTs present loops and curves while MWNTs are most of the time straight. MWNTs were the first type of CNTs that were discovered in 1991. Less than two years