Ternary pentagonal BNSi monolayer: Two-dimensional structure with potentially high carrier mobility and strong excitonic effects for photocatalytic applications

Abstract

In recent years many attempts have been made to discover new types of two-dimensional (2D) nanostructures with novel properties beyond the hexagonal crystals. The prediction of pentagraphene has sparked a great deal of research interest to investigate 2D pentagonal systems. In line with these efforts, in this paper, we propose a 2D ternary pentagonal monolayer of BNSi (penta-BNSi) and systematically investigate its structural, vibrational, mechanical, piezoelectric, electronic, photocatalytic, and optical properties by performing first-principles methods. We verify the stability of the penta-BNSi monolayer from the dynamical, thermal, and mechanical aspects based on phonon dispersion, ab initio molecular dynamics, and elastic tensor analysis, respectively. The mechanical properties are examined by calculating in-plane stiffness (Y 2D ), Poisson's ratio (ν), and ultimate tensile strength and penta-BNSi is found to be soft and ductile. The electronic structure and electronic transport calculations indicate that the penta-BNSi monolayer possesses a quasidirect band gap and anisotropic, potentially high carrier mobility. Due to the noncentral symmetric character and semiconducting feature, an intrinsic piezoelectric response emerges in the structure. In addition, penta-BNSi has a suitable band gap as well as proper band edge positions for photocatalytic water splitting within practical pH levels. The analysis of optical properties, including many-body effects, points out strong exciton binding and high light absorption in the visible and near-UV parts of the spectrum. Our findings not only expand the family of 2D pentagonal materials but also uncover an ideal ultrathin material for photocatalytic applications.

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:…”

“…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.…”

Monolayer GaOCl: a novel wide-bandgap 2D material with hole-doping-induced ferromagnetism and multidirectional piezoelectricity

“…Interestingly, such a rare piezoelectricity can be found in the GaOCl monolayer with excellent e 26 and d 26 coefficients. Compared with those of penta-BCN, 71 penta-CNP, 72 and penta-BNSi, 73 the piezoelectric performance of the GaOCl monolayer generated by in-plane shear strains is obviously much better. Therefore, with the aforementioned high piezoelectric coefficients, the GaOCl monolayer has the multifunctional piezoelectricity which is more meaningful and beneficial for nano-electromechanical devices.…”

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. ,, …”