2D clathrate graphene in minimum egg-tray-shape: An ab initio study
Abstract
The thriving area of synthetic carbon allotropes witnesses theoretic proposals and experimental syntheses of many new two-dimensional ultrathin structures, which are often achieved by careful arrangement of non-hexagon sp2 defects in graphene. Here, we introduce pyramid sp3 hybridization into sp2 network and propose a new carbon polymorph with clathrate pattern and with minimum egg-tray shape (termed as clathrate graphene). Eight symmetrically equivalent sp2 carbon atoms and two symmetrically equivalent sp2 carbon atoms in its tetragonal primitive unit cell form two perpendicularly oriented rectangles and four bridging hexagons. Though deformed bond lengths and bond angles, the planar geometry of both tetrarings and hexagons are retained. High percentage and small deformation of hexagons make this metastable sp2-sp3 allotrope comparable with pure sp2 T-graphene and penta-graphene in energetics. Exhaustive ab initio calculations confirm its dynamical and elastic stabilities, reveal its semiconducting nature with an indirect band gap of 0.90 eV for unstressed sample, and suggest a giant strain tuning effect which endows versatile electronic properties ranging from metallic to semiconducting. Furthermore, we observe multiple von Hove singularities near the Fermi energy.These salient properties may imply potential nanoelectronic applications. These findings help understand structure-property relationship for two-dimensional carbon allotropes, and help search new carbon polymorphs.