Discovering Two-Dimensional Non-van der Waals Materials

While two-dimensional (2D) materials are traditionally associated with bulk layered compounds
bonded by weak van der Waals (vdW) interactions, the recent surprising experimental realization of
non-vdW 2D compounds obtained from non-layered crystals [1,2] opens up a new direction in 2D
systems research. These materials show several distinct differences to traditional 2D sheets as their
surface was revealed to be terminated by cations rather than anions. Here, we outline several
dozens of candidates of this novel materials class derived from employing data-driven research
principles in conjunction with autonomous ab initio calculations [3,4] (Figure 1). The oxidation state
of the surface cations of the 2D sheets turns out to be an enabling descriptor regarding the
manufacturing of these systems as it determines their exfoliation energy: small oxidation states
promote easy peel off [3]. When extending the set from oxides to sulfides and chlorides, the
exfoliation energy becomes ultra low due to strong surface relaxations [4]. The materials also pass
several tests validating their vibrational and dynamic stability. The candidates exhibit a wide range of
appealing electronic, optical and in particular magnetic properties making these systems an
attractive platform for fundamental and applied nanoscience.
References
[1] A. Puthirath Balan et al., Nat. Nanotechnol. 13 (2018) 602.
[2] A. Puthirath Balan et al., Chem. Mater. 30 (2018) 5923.
[3] R. Friedrich et al., Nano Lett. 22 (2022) 989.
[4] T. Barnowsky et al., Adv. Electron. Mater. (2023) 2201112.