Inspired by the recent successful growth of Ti₂C and Ti₃C₂ monolayers, here, we investigate the structural, electronic, and mechanical properties of functionalized Ti₂C and Ti₃C₂ monolayers with chalcogenide and halogenide atoms by means of density functional theory calculations.

In a very recent accomplishment, the two-dimensional form of biphenylene network (BPN) has been fabricated. Motivated by this exciting experimental result on 2D layered BPN structure, herein we perform detailed density-functional theory-based first-principles calculations, in order to gain insight into the structural, mechanical, electronic and optical properties of this promising nanomaterial. Our theoretical results reveal the BPN structure is constructed from three rings of tetragon, hexagon and octagon, meanwhile the electron localization function shows very strong bonds between the C atoms in the structure. The dynamical stability of BPN is verified via the phonon band dispersion calculations. The mechanical properties reveal the brittle behavior of BPN monolayer. The Young’s modulus has been computed as 0.1 TPa, which is smaller than the corresponding value of graphene, while the Poisson’s ratio determined to be 0.26 is larger than that of graphene. The band structure is evaluated to show the electronic features of the material; determining the BPN monolayer as metallic with a band gap of zero. The optical properties (real and imaginary parts of the dielectric function, and the absorption spectrum) uncover BPN as an insulator along the zz direction, while owning metallic properties in xx and yy directions. We anticipate that our discoveries will pave the way to the successful implementation of this 2D allotrope of carbon in advanced nanoelectronics.

In this work, novel two-dimensional BC $$_2$$2 X (X = N, P, As) monolayers with X atoms out of the B–C plane, are predicted by means of the density functional theory. The structural, electronic, optical, photocatalytic and thermoelectric properties of the BC $$_2$$2 X monolayers have been investigated. Stability evaluation of the BC $$_2$$2 X single-layers is carried out by phonon dispersion, ab-initio molecular dynamics (AIMD) simulation, elastic stability, and cohesive energies study. The mechanical properties reveal all monolayers considered are stable and have brittle nature. The band structure calculations using the HSE06 functional reveal that the BC $$_2$$2 N, BC $$_2$$2 P and BC $$_2$$2 As are semiconducting monolayers with indirect bandgaps of 2.68 eV, 1.77 eV and 1.21 eV, respectively. The absorption spectra demonstrate large absorption coefficients of the BC $$_2$$2 X monolayers in the ultraviolet range of electromagnetic spectrum. Furthermore, we disclose the BC $$_2$$2 N and BC $$_2$$2 P monolayers are potentially good candidates for photocatalytic water splitting. The electrical conductivity of BC $$_2$$2 X is very small and slightly increases by raising the temperature. Electron doping may yield greater electric productivity of the studied monolayers than hole doping, as indicated by the larger power factor in the n-doped region compared to the p-type region. These results suggest that BC $$_2$$2 X (X = N, P, As) monolayers represent a new promising class of 2DMs for electronic, optical and energy conversion systems.

Motivated by the recent experimental realization of a two-dimensional (2D) BeN₄ monolayer, in this study we investigate the structural, dynamical, electronic, and optical properties of a monolayer and few-layer BeN₄ using first-principles calculations. The calculated phonon band dispersion reveals the dynamical stability of a free-standing BeN₄ layer, while the cohesive energy indicates the energetic feasibility of the material. Electronic band dispersions show that monolayer BeN₄ is a semi-metal whose conduction and valence bands touch each other at the Σ point. Our results reveal that increasing the layer number from single to six-layers tunes the electronic nature of BeN₄. While monolayer and bilayer structures display a semi-metallic behavior, structures thicker than that of three-layers exhibit a metallic nature. Moreover, the optical parameters calculated for monolayer and bilayer structures reveal that the bilayer can absorb visible light in the ultraviolet and visible regions better than the monolayer structure. Our study investigates the electronic properties of Dirac-semimetal BeN₄ that can be an important candidate for applications in nanoelectronic and optoelectronic.

Motivated by the successful preparation of MoSi₂N₄ monolayers in the last year [Y.-L. Hong et al., Science, 2020, 369, 670–674], the structural, electronic and optical properties of MoS₂/MoSi₂N₄ heterostructure are investigated.