Two-Dimensional Penta-NiPS Sheets: Two Stable Polymorphs

Abstract

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 α phase with an identical structure as penta-PdPSe and the newly proposed β 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 E a = 208 N m–1 and E b = 178 N m–1 for the α phase and E a = 184 N m–1 and E b = 140 N m–1 for the β phase. Interestingly, the α-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 α phase and 2.20 eV for the β phase.

Theoretically proposed stable polymorph of two-dimensional pentagonal β-PdPSe

“…The indirect band gap in the a phase was larger than that of the b phase, similar to the results of a previous study of penta-NiPS. 17 To evaluate the crystal binding stability, the cohesive energy per atom was calculated using the following equation:…”

“…We first constructed a penta-PdPSe monolayer based on the reported atomic configuration of the new polymorph, β NiPS, 17 by replacing the Ni atoms with Pd atoms and the S atoms with Se atoms. This is the β-phase, composed of two sublayers linked by the –(P–P)– bonding, as shown in Fig.…”

“…The indirect band gap in the α phase was larger than that of the β phase, similar to the results of a previous study of penta-NiPS. 17…”

“…The penta-PdPSe and penta-PdPS consist of two sublayers, an uncommon arrangement in nature that leads to unusual electronic and optical properties. [13][14][15][16] Recently, Dabsamut et al 17 reported two polymorphs of penta-NiPS (a and b phase) based on first-principle calculations. The a phase of penta-NiPS has a structure similar to the successfully synthesized penta-PdPSe, whereas the b phase of penta-NiPS was newly introduced in that work.…”

Ternary pentagonal BXN (X = C, Si, Ge, and Sn) sheets with high piezoelectricity

“…However, in recent research, the incorporating sulfur into its surface can induce piezoelectricity from non-piezoelectricity in penta -PdPSe. 15…”