Structure and stability of van der Waals layered group-IV monochalcogenides

As the quest for versatile and multifunctional 2D materials has expanded beyond graphene, hexagonal boron nitride, and transition metal dichalcogenides, van der Waals (vdW) layered monochalcogenides have gathered significant attention due to their attractive (opto)electronic, thermoelectric, and topological properties. These quasi-2D (q2D) materials are also valuable precursors for high-quality 2D materials, thus enlarging the range of materials’ properties and associated functionalities for novel applications. Using density functional theory calculations, we report on the stability of vdW-layered phases of group-IV AX monochalcogenides (where A and X belong, respectively to the sets {C, Si, Ge, Sn, Pb} and {S, Se, Te}) in six potential structural types, some of which not heretofore synthesized. We report phonon spectrum calculations and evaluate their thermodynamic stability using the formation enthalpy. Based on these results on dynamic stability and formation enthalpy of a total of 90 q2D monochalcogenide structures, we suggest that some of the new materials reported here would be synthesizable in current laboratory conditions. Our results, thus, provide guidance for future experimental synthesis and characterization studies and would enable subsequent implementation of novel AX q2D monochalcogenides in various nanoelectronic devices.