Figure 1.

(a) The schematic of “hourglass” graphene arrays structure with period (P), semimajor axis (L), semiminor axis (R). The two layers of substrate structure are Si and SiO₂. The thickness of SiO₂ is ${\mathrm{d}}_1$. (b) The side view of the structure which manipulates the chemical potential (${\mu }_c$) of graphene by applying a voltage ($V_b$).