ABSTRACT
CNTs were rst characterized by Iijima (1991) more than two decades ago. Initially, they were described as cylindrical molecules of pure carbon ranging from 1.4 nm in diameter for a single-walled nanotube (SWNT) to 30-50 nm for concentrically arranged, multiwalled nanotubes (MWNT) and possessed widely variable lengths on the order of several microns. Advances in the synthesis and processing of nanotubes have now made it possible to produce nanotubes with both well-dened wall numbers and narrow length distributions ranging from tens of nanometers (ultrashort nanotubes) to several microns. Methods to synthesize CNTs include arc discharge (Ebbesen and Ajayan 1992), laser vaporization of graphite (Puretzky et al. 2000), magnetic eld synthesis (Doherty et al. 2006), chemical vapor deposition using gaseous metal catalysts such as cobalt, nickel,
molybdenum, or iron (Cassell et al. 1999; Nobuhito et al. 2007), or water-assisted chemical vapor deposition (Hata et al. 2004).
