Intrinsic charge separation and tunable electronic band gap of armchair graphene nanoribbons encapsulated in a double-walled carbon nanotube

Recent synthesis of nanocomposite structures of graphene nanoribbons (GNRs) encapsulated in a carbon nanotube (CNT) has opened a new avenue for exploring new functionalities for applications in nanotechnology. This new class of carbon nanocomposites is expected to possess electronic properties beyond those offered by the constituent parts of nanotubes and nanoribbons; unveiling such new properties and understanding the underlying physics are among the most pressing issues in the study of these promising materials. Here, we report on first-principles calculations of the electronic properties of armchair GNRs encapsulated in a zigzag double-walled CNT. This unique structural configuration produces an intrinsic charge separation with electrons and holes localized in the outer tube and the ribbon, respectively, while the inner tube remains charge-neutral, forming an n-type/intrinsic/p-type semiconducting heterojunction due to the staggered lineup of the band structures of the constituent parts. The electronic band gap of the nanocomposite can be tuned sensitively by the changing width of encapsulated GNRs. Such intrinsic charge separation and widely tunable electronic properties without doping or an external field make this class of new carbon nanocomposites promising candidates for photovoltaic and electronics applications.