title: Exfoliation of natural van der Waals heterostructures to a single unit cell thickness.
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.
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Matěj
authors.initials: M
authors.lastname: Velický
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Peter S
authors.initials: PS
authors.lastname: Toth
authors.affiliation: School of Materials, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Rakowski
authors.affiliation: School of Materials, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Aidan P
authors.initials: AP
authors.lastname: Rooney
authors.affiliation: School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Aleksey
authors.initials: A
authors.lastname: Kozikov
authors.affiliation: School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Colin R
authors.initials: CR
authors.lastname: Woods
authors.affiliation: School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Artem
authors.initials: A
authors.lastname: Mishchenko
authors.affiliation: School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Laura
authors.initials: L
authors.lastname: Fumagalli
authors.affiliation: School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Jun
authors.initials: J
authors.lastname: Yin
authors.affiliation: School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Viktor
authors.initials: V
authors.lastname: Zólyomi
authors.affiliation: Manchester Nanomaterials Ltd, 83 Ducie Street, Manchester M1 2JQ, UK.
authors.forename: Thanasis
authors.initials: T
authors.lastname: Georgiou
authors.affiliation: School of Materials, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Sarah J
authors.identifier: 0000-0001-5509-6706
authors.initials: SJ
authors.lastname: Haigh
authors.affiliation: School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Kostya S
authors.initials: KS
authors.lastname: Novoselov
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Robert A W
authors.initials: RA
authors.lastname: Dryfe
mesh_terms: D000965:Antimony / Q000737:chemistry*; D003460:Crystallization; D004553:Electric Conductivity; D007501:Iron / Q000737:chemistry*; D007854:Lead / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D008854:Microscopy, Electron; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D056951:Photoelectron Spectroscopy; D013052:Spectrometry, X-Ray Emission; D013440:Sulfides / Q000737:chemistry*; D014001:Tin / Q000737:chemistry*
chemical_list: D013440:Sulfides; D007854:Lead; D014001:Tin; D000965:Antimony; D007501:Iron