  Based on DFT calculation, we predict that BiCN, i.e., bilayer Bi films
passivated with -CN group, is a novel 2D Bi-based material with highly
thermodynamic stability, and demonstrate that it is also a new kind of 2D TI
with a giant SOC gap (? 1 eV) by direct calculation of the topological
invariant Z2 and obvious exhibition of the helical edge states. Monolayer h-BN
and MoS2 are identified as good candidate substrates for supporting the
nontrivial topological insulating phase of the 2D TI films, since the two
substrates can stabilize and weakly interact with BiCN via van derWaals
interaction and thus hardly affect the electronic properties, especially the
band topology. The topological properties are robust against the strain and
electric field. This may provide a promising platform for realization of novel
topological phases.
