By now the carbon nanotube (CNT) has firmly established its place as a nanoscience icon and the foundation of many scientific and (increasingly nowadays) technological breakthroughs.¹  Despite having a very simple chemical composition—it is just another allotropic form of carbon—nanotubes have an astonishing variety of unique properties. A carbon nanotube is simply a nanometre-sized rolled-up graphene sheet that forms a perfect seamless cylinder (Figure 3.1) capped at the ends by fullerene caps. The structure of a simple one-shell carbon nanotube is fully defined by its roll-up vector (n,m), called chirality or helicity, which defines the position of the matched carbon rings during the roll-up of the graphene sheet.²  Significantly, this roll-up vector fully defines the nanotube morphology, diameter, and most importantly, its electronic properties. For example, an (n,m) carbon nanotube has an inner diameter, d_in, of:²