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.

Identification of Material Dimensionality Based on Force Constant Analysis

“…However, on the basis of the FC analysis, the interlayer FCs are still smaller than the intralayer FCs. Indeed, recently Friedrich et al carried out a data mining study to identify non-van der Waals 2D materials that are structurally similar to the experimentally synthesized hematene Fe 2 O 3 and ilmenite FeTiO 3 prototypes. , They identified eight binary and 20 ternary oxides, with structures similar to that of CdSnO 3 in Figure d. In the database used in our work, we could find the same four binary materials (Ga 2 O 3 , Al 2 O 3 , In 2 O 3 , and Rh 2 O 3 ) and one additional material (Sc 2 O 3 ).…”

“…A full list of the mentioned binary and ternary materials can be found in Tables S7 and S8. The important role of structural relaxation in stabilizing this type of monolayers was also discussed in refs and , while this aspect cannot be accounted for in our dimensionality classification. Other types of oxides were also identified by our approach, including ABO 4 ones, such as NbInO 4 shown in Figure b, which, to the best of our knowledge, have not been synthesized in monolayer form.…”

“…types.52,53 They identified eight binary and 20 ternary oxides, with structures similar to that of CdSnO 3 in Figure5d. In the database used in our work, we could find the same four binary materials (Ga 2 O 3 , Al 2 O 3 , In 2 O 3 , and Rh 2 O 3 ) and one additional material (Sc 2 O 3…”

Continuous chiral distances for two‐dimensional lattices

“…The former should be high, and the latter low, to guarantee stability-typically, 0.2 eV is considered an acceptable upper bound for exfoliation energy in 2D materials. 32 Figure 10 shows the positions of the oriented projected invariants PI Λ ð Þ-see QS in Figure 3-for 2D lattices of all structures in 2DMatPedia. It is immediately clear that strongly asymmetric two-dimensional materials are relatively rare in this dataset.…”

“…The database calculates two key properties that determine this—the decomposition energy, which is the energy required to split a structure into its most stable components, and the exfoliation energy, which is the average energy per atom needed to separate the modelled thin (two‐dimensional) layer from its parent material. The former should be high, and the latter low, to guarantee stability—typically, 0.2 eV is considered an acceptable upper bound for exfoliation energy in 2D materials 32 …”