Penta-SiCN: A Highly Auxetic Monolayer

The negative Poisson's (NPR) ratio in a two-dimensional (2D) material is a counterintuitive mechanical property that facilitates the development of nanoscale devices with sophisticated functionality. Inspired by the peculiar buckled lower-symmetric, trilayered geometry of pentagonal monolayers, we theoretically predict penta-SiCN, a ternary auxetic metallic monolayer with highly tunable NPR. The penta-SiCN is structurally, thermally, dynamically, and mechanically stable, and sustainable at and beyond room temperature with experimental feasibility. It possesses nontrivial geometrical and mechanical isotropy and relatively moderate thickness. Remarkably, the shorter and quasi sp(3)-hybridized C-N bond and the rigidity against the strain allow the monolayer to possess a high value of NPR (-0.136), even higher than that of black phosphorene, extendable up to -0.639 by 4% of biaxial stretching. On the other hand, the 2D Young's modulus of 129.88 N/m decreases to 41.34 N/m at equivalent stretching, indicating relative softening and flexibility. Interestingly, a buckled-to-planar phase transition is identified at 10% biaxial strain before it suffers the fracture at 16%. Additionally, the strong optical anisotropy, absorbance (up to 6.51 x 10(5) cm(-1)), and presence of plasmon frequency demonstrate its potential application in optomechanical and plasmonics.

Automated summary

A new ternary auxetic metallic monolayer, penta-SiCN, is theoretically predicted to have highly tunable negative Poisson's ratio. This monolayer exhibits structural, thermal, dynamic, and mechanical stability, making it experimentally feasible at and beyond room temperature. It also has nontrivial geometrical and mechanical isotropy.