First-principles study on the electronic and transport properties of periodically nitrogen-doped graphene and carbon nanotube superlattices

Abstract

Prompted by recent reports on $\sqrt{3} \times \sqrt{3}$ 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 $\sqrt{3} \times \sqrt{3}$ superlattices of graphene and carbon nanotubes. Multiple nanostructures of $\sqrt{3} \times \sqrt{3}$ graphene ribbons and carbon nanotubes are explored, and all configurations show nonmagnetic and metallic behaviors. The transport properties of $\sqrt{3} \times \sqrt{3}$ 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 $\sqrt{3} \times \sqrt{3}$ armchair carbon nanotube heterostructure shows quantized behavior under certain circumstances.

Figures (7)

• Figure 1: Top views of the geometric structures of (a) 2-dimensional nitrogen-doped graphene superlattice, (b) 12-zigzag ribbon (ZGR1), (c) 12-zigzag ribbon (ZGR2), (d) 12-zigzag ribbon (ZGR3), (e) 18-armchair ribbon (AGR1), and (f) 18-armchair ribbon (AGR2). The nanoribbons are extended periodically along the $y$ direction, as indicated by the blue arrows. The white, gray, and blue balls represent the hydrogen, carbon, and nitrogen atoms, respectively.
• Figure 2: Two-probe configurations of (a) 12-zigzag nitrogen-doped graphene ribbon, and (b) (6,6)-armchair nitrogen-doped CNT sandwiched between pristine zigzag graphene ribbons and armchair CNTs, respectively. The white, gray, and blue balls denote the hydrogen, carbon, and nitrogen atoms, respectively. The orange regions represent the lead regions.
• Figure 3: Electronic band structures of $\sqrt{3} \times \sqrt{3}$ nitrogen-doped graphene ribbons: (a) 12-ZGR1, (b) 12-ZGR2, (c) 18-ZGR2, and (d) 12-ZGR3. The corresponding geometries are shown in Fig. \ref{['fig1']}.
• Figure 4: Electronic band structures of $\sqrt{3} \times \sqrt{3}$ nitrogen-doped armchair graphene ribbons, (a) 18-AGR1, and (b) 18-AGR2. The spatial configurations of AGR1 and AGR2 are visualized in Fig. \ref{['fig1']}(e) and Fig. \ref{['fig1']}(f), respectively.
• Figure 5: (a) Evolution of band gap $\Delta$ of the nitrogen-doped zigzag graphene ribbons as a function of ribbon width N$_\textrm{z}$. (b) Band gap $\Delta$ of $\sqrt{3} \times \sqrt{3}$ armchair ribbons versus ribbon width N$_\textrm{a}$.