▎ 摘　　要

Prompted by recent reports on root 3 x root 3 graphene superlattices with intrinsic inter-valley interactions, we perform first-principles calculations to investigate the electronic properties of periodically nitrogen-doped graphene and carbon nanotube nanostructures. In these structures, nitrogen atoms substitute one-sixth of the carbon atoms in the pristine hexagonal lattices with exact periodicity to form perfect root 3 x root 3 superlattices of graphene and carbon nanotubes. Multiple nanostructures of root 3 x root 3 graphene ribbons and carbon nanotubes are explored, and all configurations show nonmagnetic and metallic behaviors. The transport properties of root 3 x root 3 graphene and carbon nanotube superlattices are calculated utilizing the non-equilibrium Green's function formalism combined with density functional theory. The transmission spectrum through the pristine and root 3 x root 3 armchair carbon nanotube heterostructure shows quantized behavior under certain circumstances.