Tunable structural phases and electronic properties of group V MSi2N4 (M = V, Nb, Ta) nanosheets via surface hydrogenation: a first-principles study

Abstract

In recent experiments, researchers have discovered a new family of layered MA₂Z₄ materials, which exhibit fascinating phase-dependent electronic properties. Here, we have performed a comprehensive first-principles calculation to investigate the hydrogenation effects on the structural phases and electronic properties of group V MSi₂N₄ (M = V, Nb, Ta) nanosheets. It is found that the hydrogenation will induce structural transitions through layer gliding in both the SiN surface layers and the central MN₂ part. The tetrahedral coordination of Si atoms will be transformed into the octahedral one, which gives rise to an Hα-to-Hβ transition in the semihydrogenated system. When the system is fully hydrogenated, the central MN2 layer will further experience an H-to-T phase transition due to the change of d electron count. Accompanied with these phase transitions, the electronic properties of the MSi₂N₄ nanosheets are affected remarkably, and they will be converted into small-gap semiconductors/metals by the semi-/full- hydrogenation. In particular, due to the Janus structure of semi-hydrogenated MSi₂N₄H₁ nanosheets, their band gaps can be substantially modulated by the electric field and high solar-to-hydrogen efficiencies of 18–20% are present in these systems. Our study demonstrates that surface hydrogenation is an effective way to tune the geometrical and electronic structures of group V MSi₂N₄ nanosheets, which allows them to have fascinating electronic and photocatalytic applications.