Two-dimensional Dirac half-metal in porous carbon nitride C6N7monolayer via atomic doping.

Motivated by the recent experimental discovery of C6N7monolayer (Zhaoet al2021Science Bulletin66, 1764), we show that C6N7monolayer co-doped with C atom is a Dirac half-metal by employing first-principle density functional theory calculations. The structural, mechanical, electronic and magnetic properties of the co-doped C6N7are investigated by both the PBE and HSE06 functionals. Pristine C6N7monolayer is a semiconductor with almost isotropic electronic dispersion around the Γ point. As the doping of the C6N7takes place, the substitution of an N atom with a C atom transforms the monolayer into a dilute magnetic semiconductor, with the spin-up channel showing a band gap of 2.3 eV, while the spin-down channel exhibits a semimetallic phase with multiple Dirac points. The thermodynamic stability of the system is also checked out via AIMD simulations, showing the monolayer to be free of distortion at 500 K. The emergence of Dirac half-metal in carbon nitride monolayer via atomic doping reveals an exciting material platform for designing novel nanoelectronics and spintronics devices.

Surface modification of titanium carbide MXene monolayers (Ti2C and Ti3C2) via chalcogenide and halogenide atoms.

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 by means of density functional theory calculations. The results reveal that monolayers of Ti2C and Ti3C2 are dynamically stable metals. Phonon band dispersion calculations demonstrate that two-surface functionalization of Ti2C and Ti3C2via chalcogenides (S, Se, and Te), halides (F, Cl, Br, and I), and oxygen atoms results in dynamically stable novel functionalized monolayer materials. Electronic band dispersions and density of states calculations reveal that all functionalized monolayer structures preserve the metallic nature of both Ti2C and Ti3C2 except Ti2C-O2, which possesses the behavior of an indirect semiconductor via full-surface oxygen passivation. In addition, it is shown that although halide passivated Ti3C2 structures are still metallic, there exist multiple Dirac-like cones around the Fermi energy level, which indicates that semi-metallic behavior can be obtained upon external effects by tuning the energy of the Dirac cones. In addition, the computed linear-elastic parameters prove that functionalization is a powerful tool in tuning the mechanical properties of stiff monolayers of bare Ti2C and Ti3C2. Our study discloses that the electronic and structural properties of Ti2C and Ti3C2 MXene monolayers are suitable for surface modification, which is highly desirable for material property engineering and device integration.

First-principles investigation of nonmetal doped single-layer BiOBr as a potential photocatalyst with a low recombination rate.

Nonmetal doping is an effective approach to modify the electronic band structure and enhance the photocatalytic performance of bismuth oxyhalides. Using density functional theory, we systematically examine the fundamental properties of single-layer BiOBr doped with boron (B) and phosphorus (P) atoms. The stability of the doped models is investigated based on the formation energies, where the substitutional doping is found to be energetically more stable under O-rich conditions than under Bi-rich ones. The results showed that substitutional doping of P atoms reduced the bandgap of pristine BiOBr to a greater extent than that of boron substitution. The calculation of the effective masses reveals that B doping can render the electrons and holes of pristine BiOBr lighter and heavier, respectively, resulting in a slower recombination rate of photoexcited electron-hole pairs. Based on the results of HOMO-LUMO calculations, the introduction of B atoms tends to increase the number of photocatalytically active sites. The top of the valence band and the conduction band bottom of the B doped BiOBr monolayer match well with the water redox potentials in an acidic environment. The absorption spectra propose that B(P) doping causes a red-shift. Overall, the results predict that nonmetal-doped BiOBr monolayers have a reduced bandgap, a slow recombination rate, more catalytically active sites, enhanced optical absorption edges, and reduced work functions, which will contribute to superior photocatalytic performance.