Unexpected buckled structures and tunable electronic properties in arsenic nanosheets: insights from first-principles calculations.

Using dispersion-corrected density functional theory calculations, we investigate the structural and electronic properties of arsenic (As) nanosheet, which is a cousin of phosphorene. We find that the black-phosphorus like structure is dynamically unstable for As, which has an out-of-plane soft mode from its flat As zigzag lines. Hence different from phosphorene, the stable As monolayer possesses a unique buckling along the zigzag direction, which leads to a surface corrugation of 0.20 Å and a robust dynamic stability. The zigzag buckling alters the band feature of As nanosheet, transforming it from an indirect band gap semiconductor to a direct one for the buckled structure. Strain engineering can further tune the surface corrugation and band structure of As nanosheet, for which the direct or indirect gap feature can be switched by the zigzag-directional strains, while the strains along armchair direction could modulate the band gap and induce a metallic behaviour. Prominent anisotropic Dirac-like electronic structures and orientation-dependent elastic behaviours with a remarkable negative Poisson ratio are both found in the As nanosheets, enabling the system promising applications for nano-electrics and devices.