Tunable band gap of graphyne-based homo- and hetero-structures: effects of stacking sequence, strain and external electric field

Two-dimensional van der Waals (vdW) layered materials have attracted great attention for their possible applications in flexible electronics and optoelectronics. In this work, we report a comprehensive theoretical study of graphyne/graphyne (Gyne/Gyne), graphyne-like BN/graphyne-like BN (BNyne/BNyne) and graphyne/graphyne-like BN (Gyne/BNyne) bilayers by density functional theory. These bilayers exhibit distinct stacking dependent characteristics in the ground state electronic structure and have different responses to external strain and electric field. For Gyne/Gyne and Gyne/BNyne bilayers, a biaxial tensile strain increases the band gap while biaxial compressive strain or uniaxial strain, reduces it. For theBNyne/BNyne bilayer the trend is opposite. Under a vertical electric field, the band gap decreases in homo-bilayers Gyne/Gyne and BNyne/BNyne. For the hetero-bilayer Gyne/BNyne, band gap decreases under a positive electric fieldbut remain almost constant in negative electric field. These properties are understood by analyzing the calculated electronic density and potential.