A New Group of 2D Non-van der Waals Materials with Ultra Low Exfoliation Energies

Abstract

The exfoliation energy—quantifying the energy required to extract a two-dimensional (2D) sheet from the surface of a bulk material—is a key parameter determining the synthesizability of 2D compounds. Here, using ab initio calculations, a new group of non-van der Waals 2D materials derived from non-layered crystals that exhibit ultra low exfoliation energies is presented. In particular for sulfides, surface relaxations are essential to correctly describe the associated energy gain needed to obtain reliable results. Taking into account long-range dispersive interactions has only a minor effect on the energetics and ultimately proves that the exfoliation energies are close to the ones of traditional van der Waals bound 2D compounds. The candidates with the lowest energies, 2D SbTlO3 and MnNaCl3, exhibit appealing electronic, potential topological, and magnetic features as evident from the calculated band structures making these systems an attractive platform for fundamental and applied nanoscience.