A New Group of Two-Dimensional Non-van der Waals Materials with Ultra Low Exfoliation Energies

TL;DR

This paper introduces a new class of non-van der Waals 2D materials with ultra low exfoliation energies, expanding the range of synthesizable 2D compounds with promising electronic and magnetic properties.

Contribution

It identifies non-layered crystals as a source of 2D materials with low exfoliation energies, supported by ab initio calculations including surface relaxations and dispersive interactions.

Findings

Exfoliation energies are comparable to van der Waals 2D materials.

Surface relaxations are crucial for accurate energy calculations.

Some candidates exhibit promising electronic, topological, and magnetic features.

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, we present a new group of non-van der Waals 2D materials derived from non-layered crystals which exhibit ultra low exfoliation energies. 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 SbTlO$_3$ and MnNaCl$_3$, 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.