Two-Dimensional C4N Global Minima: Unique Structural Topologies and Nanoelectronic Properties

Atomically thin 2D materials have drawn great attention due to their many potential applications. We herein report two novel structures of 2D C4N identified by first principles calculations in combination with a swarm structure search. These two structures (with symmetry of PM and P2/m) are almost degenerate in energy (with only 4 meV/atom difference) and exhibit quite similar structural topologies, both consisting of alternative arrays of C-N hexagon and arrays of C-N pentagon-octagon-pentagon. The Pm structure is semiconducting with a direct band gap of 90 meV at HSE. In contrast, the P2/m structure is a zero-band-gap semimeIal and possesses the distorted Dirac cone, showing the direction-dependent Fermi velocity land electronic properties. Thus the predicted C4N monolayers are promising for applications in nanoelectronics.