We report the structural, electronic, magnetic, and elastic properties of a two-dimensional (2D) honeycomb stannic oxide (SnO) monolayer based on comprehensive first-principles calculations. The free-standing and well-ordered 2D centered honeycomb SnO (T-SnO) monolayer with D point-group symmetry has good dynamical stability, as well as thermal stability at 500 K. The T-SnO monolayer is a nonmagnetic wide-bandgap semiconductor with an indirect bandgap of 2.55/4.13 eV obtained by the generalized gradient approximation with the Perdew-Burke-Ernzerhof/Heyd-Scuseria-Ernzerhof hybrid functional, but it acquires a net magnetic moment upon creation of a Sn vacancy defect. The elastic constants obtained from the relaxed ion model show that the T-SnO monolayer is much softer than MoS. The bandgap monotonically decreases with increasing strain from -8% to 15%. An indirect-to-direct bandgap transition occurs upon applying biaxial strain below -8%. Synthesis of the T-SnO monolayer is proposed. We identify the Zr(0001) surface as being suitable to grow and stabilize the T-SnO monolayer. The unique structure and electronic properties mean that the T-SnO monolayer has promising applications in nanoelectronics. We hope that the present study on the stable free-standing SnO monolayer will inspire researchers to further explore its importance both experimentally and theoretically.

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We have investigated the structures, electronic structures and magnetic properties of the triazine-based g-C3N4 (gt-C3N4) monolayer doped with B, Al, and Cu atoms based on density functional theory using ab initio calculations. The B atom prefers to be situated at the center of the triazine ring, whereas the Al and Cu atoms tend to be located above the center of the triazine ring. The doping at the interstitial sites results in nonplanar structures which are thermodynamically stable. Each dopant atom induces a total magnetic moment of 1.0 μB which mainly arises from the pz orbitals because the n-type doping injects unpaired electrons into anti-π orbitals. The results obtained from the GGA-PBE and HSE06 schemes show that all the doped systems exhibit half-metallic behaviors. B- and Al-doped systems are at a ferromagnetic ground state, while the Cu-doped case is at an anti-ferromagnetic ground state. The long-range half-metallic ferromagnetic order is attributed to the p-p interactions. In particular, the estimated Curie temperature implies that the systems doped with B are potential candidates for spintronics applications in future.

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