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).
Acknowledgements:
The authors thank the HZDR Computing Center, HLRS, Stuttgart, Germany, and TU Dresden
Cluster “Taurus” for generous grants of CPU time. R.F. acknowledges support from the
Alexander von Humboldt foundation under the Feodor Lynen research fellowship. A.V.K. thanks
the German Research Foundation (DFG) for the support through Project KR 4866/2-1 and the
collaborative research center “Chemistry of Synthetic 2D Materials” SFB-1415-417590517.