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Exfoliation of natural van der Waals heterostructures to a single unit cell thickness.

Matěj VelickýPeter S TothAlexander M RakowskiAidan P RooneyAleksey KozikovColin R WoodsArtem MishchenkoLaura FumagalliJun YinViktor ZólyomiThanasis GeorgiouSarah J HaighKostya S NovoselovRobert A W Dryfe
Published in: Nature communications (2017)
Weak interlayer interactions in van der Waals crystals facilitate their mechanical exfoliation to monolayer and few-layer two-dimensional materials, which often exhibit striking physical phenomena absent in their bulk form. Here we utilize mechanical exfoliation to produce a two-dimensional form of a mineral franckeite and show that the phase segregation of chemical species into discrete layers at the sub-nanometre scale facilitates franckeite's layered structure and basal cleavage down to a single unit cell thickness. This behaviour is likely to be common in a wider family of complex minerals and could be exploited for a single-step synthesis of van der Waals heterostructures, as an alternative to artificial stacking of individual two-dimensional crystals. We demonstrate p-type electrical conductivity and remarkable electrochemical properties of the exfoliated crystals, showing promise for a range of applications, and use the density functional theory calculations of franckeite's electronic band structure to rationalize the experimental results.
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