Penta-SiCN: A Highly Auxetic Monolayer

Abstract

The negative Poisson's (NPR) ratio in a twodimensional (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× 10 5 cm −1 ), and presence of plasmon frequency demonstrate its potential application in optomechanical and plasmonics.

A penta-BCP sheet with strong piezoelectricity and a record high positive Poisson's ratio

“…To identify the chemical stability of penta-BCP, we calculate the cohesive energy ( E coh ) of penta-BCP, which is defined as E coh = ( E penta-BCP − 2 E B − 2 E C − 2 E P )/6, where E B , E C , E P , and E penta-BCP represent the energy of an isolated B atom, C atom, P atom, and a unit cell of penta-BCP, respectively. The resulting cohesive energy of penta-BCP is −5.61 eV per atom, which is comparable to that of many other ternary monolayers such as penta-BNSi (−5.43 eV per atom), 37 penta-SiCN (−4.36 eV per atom), 38 BPC 2 (−5.77 eV per atom), 39 and BiPbC 3 (−5.62 eV per atom), 40 indicating its energetic stability. We also calculate the formation energy ( E form ) of penta-BCP ( E form ) defined as: E form = ( E penta-BCP − 2 E B s − 2 E C s − 2 E P s )/6, where E B s , E C s , and E P s represent the energy of each B, C, and P atom in its most stable bulk phase, respectively.…”

“…, where E B , E C , E P , and E penta-BCP represent the energy of an isolated B atom, C atom, P atom, and a unit cell of penta-BCP, respectively. The resulting cohesive energy of penta-BCP is À5.61 eV per atom, which is comparable to that of many other ternary monolayers such as penta-BNSi (À5.43 eV per atom), 37 penta-SiCN (À4.36 eV per atom), 38 BPC 2 (À5.77 eV per atom), 39 and BiPbC 3 (À5.62 eV per atom), 40 indicating its energetic stability. We also calculate the formation energy (E form ) of penta-BCP (E form ) defined as:…”

“…50 It is also worth mentioning that the Poisson's ratio of penta-BCP has a negative value of À0.28 for y = 481 and its equivalents. The absolute value is larger than that of penta-CNP (À0.04) 17 and penta-SiCN (À0.132), 38 which shows its potential application in nanomechanical devices as a nano-auxetic material. Because the in-plane projections of C-B and C-P bonds are close to the [110] direction and its equivalents, the values of both y 1 (B 1 -C-P 1 ) and y 2 (B 2 -C-P 2 ) increase with tensile strain applied along the [110] direction.…”

“…Note that the Young's moduli of penta-BCP are comparable to those of black phosphorene (23.0-92.3 GPa). 44 By contrast, they are smaller than those of penta-BCN (189-223 N m À1 ), 16 penta-CNP (172-190 N m À1 ), 17 penta-BNSi (109-113 N m À1 ), 37 and penta-SiCN (129.88-131.29 N m À1 ), 38 and they are much smaller compared with those of some common 2D materials such as graphene (340 N m À1 ), 45 h-BN (275.8 N m À1 ), 42 and MoS 2 (180 N m À1 ), 46 suggesting that penta-BCP possesses weak mechanical strength. Therefore, it can be expected that penta-BCP could possess larger piezoelectric coefficients than penta-BCN and penta-CNP.…”

Large Negative Poisson’s Ratio and Anisotropic Mechanics in New Penta-PBN Monolayer

“…In recent years, a new class of two-dimensional (2D) Cairo-pentagonal lattice monolayers and their one-dimensional (1D) nanoribbon are drawing considerable attention due to their extraordinary chemical and physical properties , identified by both experiments − and theories. − Unlike ultra-thin planar hexagonal graphene, the low-symmetric, trilayered, and buckled geometry of penta monolayers allow them more degrees of freedom to possess novel mechanical, piezoelectric, electronic, thermal, and optical properties. − In addition, the inheritance of the robust band topology and visible light-harvesting direct-band gap semiconducting to metallic electronic behavior of penta monolayers make them highly desirable in cutting-edge technological devices such as optomechanical sensors, lithium-ion batteries, and solar cells. ,, …”