Strain-Field-Induced Bandgap Opening in Bilayer Graphene.

Opening a bandgap in bilayer graphene typically requires either structural modification or continuous external electric fields, while twisted bilayer graphene configurations remain largely gapless without additional perturbation. Here, we demonstrate bandgap opening of up to 50 meV in structurally intact bilayer graphene by in-plane strain fields imposed by an interfaced porous organic 2D crystal. These sandwich graphene/organic 2D crystal/graphene (G-O2DC-G) heterostructures, with O2DCs of honeycomb lattice structure and with pore sizes ranging from 9.6 to 31.0 Å, template corrugation that brings graphene layers into localized Bernal-stacked contact within the pores. We identify a critical pore size threshold of ∼18 Å, above which the graphene layers establish direct contact with interlayer spacing of ∼3.34 Å as in Bernal-stacked bilayer. The bandgap exhibits a non-monotonic dependence on pore size, reaching its maximum at ∼19 Å (G-TTI-G) before declining with further pore expansion. We propose this strain-based approach as a design principle for bandgap engineering in graphene, leveraging the chemical diversity of O2DCs for potential applications in graphene-based semiconductor devices.