Data-Driven Design of Two-Dimensional Non-van der Waals Materials

Two-dimensional (2D) materials are traditionally associated with the sheets forming
bulk layered compounds bonded by weak van der Waals (vdW) forces with graphene
derived from bulk graphite being the most prominent example. The weak inter-layer
interaction leads to a natural structural separation of the 2D subunits in the crystals,
giving rise to the possibility of mechanical and liquid-phase exfoliation. The anisotropic
interaction also provided suitable structural criteria for the computational search for
such traditional 2D materials which predicted about 2000 exfoliable compounds [1].
However, the unexpected experimental realization of atomically thin sheets from
non-vdW bonded compounds, for which the previously formulated descriptors are
not applicable, recently opened up a new direction in the research on 2D materials
[2]. These non-vdW 2D compounds exhibit qualitatively new features due to the
unsaturated bonds at their surfaces. Here, we present our recent data-driven search
for representatives of this novel materials class [3]. By screening the AFLOW
database according to structural prototype information 28 new, potentially
synthesizable candidates are outlined. The oxidation state of the surface cations is
found to regulate the exfoliation energy with low oxidation numbers giving rise to
weak bonding – thus providing an enabling descriptor to obtain novel 2D materials.
The candidates showcase a versatile spectrum of appealing electronic, optical and
magnetic properties suggesting in particular spintronic applications.
[1] N. Mounet et al., Nat. Nanotechnol. 13, 246 (2018).
[2] A. Puthirath Balan et al., Nat. Nanotechnol. 13, 602 (2018).
[3] R. Friedrich et al. Nano Lett. 22, 989 (2022).