Promising mechanical, electronic and piezoelectric properties of grapheneplus-like BCN monolayer: insights from...

Two-dimensional (2D) carbon allotropes, together with their binary and ternary counterparts, have attracted substantial research interest due to their peculiar geometries and properties. Among them, grapheneplus, a derivative of penta-graphene, has been proposed to exhibit unusual mechanical and electronic behaviour. In this work, we perform a comprehensive first-principles study on its isoelectronic and isostructural analogue, a grapheneplus-like BCN (gp-BCN) monolayer. It is found that this gp-BCN system exhibits robust structural stability from energetic, dynamic, thermal, and mechanical perspectives. A remarkable anisotropy is observed in its mechanical behaviour, which even presents in-plane auxeticity with a high negative Poisson's ratio of -0.3. Different from the semimetallic grapheneplus one, the gp-BCN monolayer is a semiconductor with a direct band gap of 3.23 eV. High electron mobilities up to 10³ cm² V^-1 s^-1 appear in the gp-BCN system, which are one to two orders of magnitude greater than the hole mobilities. Furthermore, due to the breaking of inversion symmetry, the gp-BCN monolayer exhibits spontaneous out-of-plane polarization, yielding prominent out-of-plane piezoelectric responses that are comparable to those of Janus MoSSe, WSSe and H-decorated BN systems. Our study demonstrates that the BCN analogue of grapheneplus possesses promising mechanical, electronic, and piezoelectric properties, rendering it promising for applications in nanoelectronics and mechanical nanosensors.