Two-Dimensional Non-van der Waals Materials by Design

Two-dimensional (2D) materials are traditionally derived from bulk layered compounds bonded by weak
van der Waals (vdW) forces. In this context, the recent surprising experimental realization of non-vdW
2D compounds obtained from non-layered crystals [1,2] foreshadows a new direction in 2D systems
research. These materials are distinct from traditional 2D sheets as their surface was revealed to be
terminated by cations rather than anions.
Here, we present several dozens of candidates of this novel materials class derived from applying data-driven
research methodologies in conjunction with autonomous ab initio calculations and also outline
how to tune their properties [3,4]. We find that the oxidation state of the surface cations of the
2D sheets is 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 magnetic properties which can be tuned by proper
chemical functionalization of the 2D sheets making these systems an attractive platform for fundamental
and applied nanoscience.
References
[1] A. Puthirath Balan et al., Nat. Nanotechnol. 13, 602 (2018).
[2] A. Puthirath Balan et al., Chem. Mater. 30, 5923 (2018).
[3] R. Friedrich et al., Nano Lett. 22, 989 (2022).
[4] T. Barnowsky et al., Adv. Electron. Mater. 2201112 (2023).