  Due to the noticeable structural similarity and being neighborhood in
periodic table of group-IV and -V elemental monolayers, whether the combination
of group-IV and -V elements could have stable nanosheet structures with
optimistic properties has attracted great research interest. In this work, we
performed first-principles simulations to investigate the elastic, vibrational
and electronic properties of the carbon nitride (CN) nanosheet in the puckered
honeycomb structure with covalent interlayer bonding. It has been demonstrated
that the structural stability of CN nanosheet is essentially maintained by the
strong interlayer \so\ bonding between adjacent carbon atoms in the opposite
atomic layers. A negative Poisson's ratio in the out-of-plane direction under
biaxial deformation, and the extreme in-plane stiffness of CN nanosheet, only
slightly inferior to the monolayer graphene, are revealed. Moreover, the highly
anisotropic mechanical and electronic response of CN nanosheet to tensile
strain have been explored.
