Computational characterization of monolayer C3N: A two-dimensional nitrogen-graphene crystal

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Invited Articles

Contributing Editor: Venkatesan Renugopalakrishnan

I.

INTRODUCTION

The carbon-nitrogen (C-N) compounds have long been attracting interest due to their versatile and unique properties. It is known that diamond is the hardest material in nature with measured Vickers hardness up to 120 GPa.¹Liu and Cohen²creatively predicted that[...]-C₃N₄ with the ultrahigh bulk modulus of ~430 GPa is a superhard material even harder than diamond, which highlights the pivotal role of strongly covalent C-N bonds. Although[...]-C₃N₄ as a hypothetical material has not yet be synthesized, it stimulates intensive studies on the carbon nitrides with manifold stoichiometries, including sp³-hybridized dense phases (CN,^3,4C₃N₂,⁵C₃N,^4,6etc.) and sp²-hybridized graphitic phases (CN,⁴C₃N,^4,6-8etc.), which are typically useful for superhard materials⁹and (photo) catalyst,^10,11respectively.

In two-dimensional (2D) scenario, graphene, a single-layer of carbon atoms arranged in a honeycomb lattice, possesses superior physical and chemical properties and carries great promise for various device applications.¹²In particular, graphene is the strongest 2D material which exhibits ultra-high Young's modulus and unsurpassed tensile strength.¹³Doping graphene with nitrogen atoms is widely considered an effective way to further tailor its electronic structure as well as other physical and chemical properties.^14,15Monolayer C₃N, a kind of 2D nitrogen-graphene crystal, was first reported to be an indirect band-gap semiconductor by Mizuno et al.¹⁶using early-stage electronic structure method. Recently, Hu et al.⁸suggested three possible planar structures of C₃N and the most stable one in energy is the same as that proposed in Ref. 16. By using the cluster-expansion and particle-swarm optimization algorithms, Xiang et al.¹⁷studied in detail the C-N phase separation in nitrogen-doped graphene and two stable, ordered, and semiconducting nitrogen-graphene crystals, C₃N and C₁₂N, are revealed. Up to date, only monolayer C₃N is synthesized in experiment via the direct pyrolysis of hexaaminobenzene trihydrochloride single crystals in the solid state.¹⁸Very recently, Yang et al.¹⁹fabricated large-scale C₃N nanostructures from the polymerization of 2,3-diaminophenazine by...