Abstract
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.
Highlights
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
The density functional theory (DFT) calculations of franckeite’s electronic band structure indicate only weak interactions between the individual van der Waals layers, confirmed by the independence of franckeite’s Raman spectrum of the number of layers and the incommensurate lattice matching observed by the high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM)
The TEM-energy-dispersive X-ray spectroscopy (EDXS) elemental maps in Fig. 1d–h show that the main elements, lead, tin, antimony, iron and sulphur, are homogeneously distributed when viewed perpendicular to the layers
Summary
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. 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 singlestep synthesis of van der Waals heterostructures, as an alternative to artificial stacking of individual two-dimensional crystals. The density functional theory (DFT) calculations of franckeite’s electronic band structure indicate only weak interactions between the individual van der Waals layers, confirmed by the independence of franckeite’s Raman spectrum of the number of layers and the incommensurate lattice matching observed by the high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM)
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