Two-Dimensional Penta-NiPS Sheets: Two Stable Polymorphs

The discovery of new and stable two-dimensional (2D) materials with exotic properties is essential for technological advancement. Inspired by the recently reported penta-PdPSe, we proposed penta-NiPS as a new member of the penta-2D materials based on first-principles calculations. The penta-NiPS monolayer is stable in two polymorphs including the alpha phase with an identical structure as penta-PdPSe and the newly proposed beta phase with rotated sublayers. Comprehensive analyses indicated that both phases are thermodynamically, dynamically, mechanically, and thermally stable. The penta-NiPS is a soft material with 2D Young's modulus of Ea = 208 N m-1 and Eb = 178 N m-1 for the alpha phase and Ea = 184 N m-1 and Eb = 140 N m-1 for the beta phase. Interestingly, the alpha-penta-NiPS showed nearly zero Poisson's ratios along the in-plane direction, where its dimensions would be maintained when being extended. For electronic application, we demonstrated that penta-NiPS is a wide band gap semiconductor with an indirect band gap of 2.35 eV for the alpha phase and 2.20 eV for the beta phase.

Automated summary

The discovery of new and stable two-dimensional materials is crucial for technological advancement. In this study, penta-NiPS is proposed as a new member of the penta-2D materials based on calculations, and its stability and properties are comprehensively analyzed.