Computational characterization of monolayer C 3 N: A two-dimensional nitrogen-graphene crystal
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Carbon–nitrogen compounds have attracted enormous attention because of their unusual physical properties and fascinating applications on various devices. Especially in two-dimension, doping of nitrogen atoms in graphene is widely believed to be an effective mechanism to improve the electronic and optoelectronic performances of graphene. In this work, using the first-principles calculations, we systematically investigate the electronic, mechanical, and optical properties of monolayer C3N, a newly synthesized two-dimensional carbon-graphene crystal. The useful results we obtained are: (i) monolayer C3N is an indirect band-gap semiconductor with the gap of 1.042 eV calculated by the accurate hybrid functional; (ii) compared with graphene, it has smaller ideal tensile strength but larger in-plane stiffness; (iii) the nonlinear effect of elasticity at large strains is more remarkable in monolayer C3N; (iv) monolayer C3N exhibits main absorption peak in visible light region and secondary peak in ultraviolet region, and the absorbing ratio between them can be effectively mediated by strain.
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.1 Liu and Cohen2 creatively predicted that b-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 b-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,3,4 C3N2,5 C3N,4,6 etc.) and sp2-hybridized graphitic phases (CN,4 C3N,4,6–8 etc.), which are typically useful for superhard materials9 and (photo) catalyst,10,11 respectively. In two-dimensional (2D) scenario, graphene, a singlelayer of carbon atoms arranged in a honeycomb lattice, possesses superior physical and chemical properties and carries great promise for various device applications.12 In particular, graphene is the strongest 2D material which exhibits ultra-high Young’s modulus and unsurpassed tensile strength.13 Doping graphene with nitrogen atoms is widely considered an effective way to further tailor its electronic structure as well as other physical and chemical properties.14,15 Monolayer C3N, a kind of 2D Contributing Editor: Venkatesan Renugopalakrishnan a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.228
nitrogen-graphene crystal, was first reported to be an indirect band-gap semiconductor by Mizuno et al.16 using early-stage electronic structure method. Recently, Hu et al.8 suggested 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.17 studied in detail the C–N phase separation in nitrogendop
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