Electronic properties of nanotube-ribbon hybrid systems

In this work we use the tight-binding model to study the electronic properties of nanotube-ribbon hybrid systems. The nanotube-ribbon interactions will modify state energies, alter energy gaps, destroy state degeneracy, and create additional band-edge states. The bandstructures are asymmetric and symmetric about the Fermi energy when the interactions are turned on and off, respectively. The energy gap is found to vary sensitively with the nanotube location. Moreover, semiconductor-metal transition is predicted for nanotube-ribbon hybrid systems (I) and (III). For a zigzag ribbon, the partial flat bands at E_F are almost unaffected by the nanotube-ribbon coupling although the bandstructures have been noticeably modified by such coupling; the energy gap of system (IV) is always zero. The effects of nanotube diameter and ribbon width on the energy gap and the density of states are also investigated. The semiconductor-metal transition can be accomplished by varying the nanotube location, the nanotube diameter or the ribbon width. The main features of the bandstructure are directly reflected in the density of states. The numbers, heights, and energies of the density of states peaks are strongly dependent on the nanotube-ribbon hoppings.