Quantum confinement in carbon-nanotube systems

Carbon nanotubes are graphene cylinders of nanometric diameter which can be either semiconducting or metallic depending on their geometry. Joining different kinds of nanotubes by means of topological defects, one can design all-carbon quantum dots and, in principle, achieve electronic confinement in quasi-zerodimensional systems. In this work we review different ways of quantum electron confinement in carbon nanotubes: by matching a finite metallic nanotube portion to two semi-infinite semiconducting nanotubes, quantum dot states appear in the system due to confinement by energy barriers all-metallic carbon nanotube structures are shown to have completely localised states because of the symmetry gap between the nanotube components quasi-localised states, showing up as sharp resonances, are demonstrated to arise as a result of wavevector mismatch in all-metallic systems made of nanotubes without any common symmetry. The different conductance behaviour of the various structures is also studied.