title: Franckeite as a naturally occurring van der Waals heterostructure.
abstract: The fabrication of van der Waals heterostructures, artificial materials assembled by individual stacking of 2D layers, is among the most promising directions in 2D materials research. Until now, the most widespread approach to stack 2D layers relies on deterministic placement methods, which are cumbersome and tend to suffer from poor control over the lattice orientations and the presence of unwanted interlayer adsorbates. Here, we present a different approach to fabricate ultrathin heterostructures by exfoliation of bulk franckeite which is a naturally occurring and air stable van der Waals heterostructure (composed of alternating SnS2-like and PbS-like layers stacked on top of each other). Presenting both an attractive narrow bandgap (<0.7 eV) and p-type doping, we find that the material can be exfoliated both mechanically and chemically down to few-layer thicknesses. We present extensive theoretical and experimental characterizations of the material's electronic properties and crystal structure, and explore applications for near-infrared photodetectors.
authors.affiliation: Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid, Spain.
authors.forename: Aday J
authors.initials: AJ
authors.lastname: Molina-Mendoza
authors.affiliation: Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Campus de Cantoblanco, E-28049 Madrid, Spain.
authors.forename: Emerson
authors.initials: E
authors.lastname: Giovanelli
authors.affiliation: Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid, Spain.
authors.forename: Wendel S
authors.initials: WS
authors.lastname: Paz
authors.affiliation: Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Campus de Cantoblanco, E-28049 Madrid, Spain.
authors.forename: Miguel Angel
authors.initials: MA
authors.lastname: Niño
authors.affiliation: Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands.
authors.forename: Joshua O
authors.initials: JO
authors.lastname: Island
authors.affiliation: Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid, Spain.
authors.forename: Charalambos
authors.initials: C
authors.lastname: Evangeli
authors.affiliation: ALBA Synchrotron Light Facility, Carrer de la Llum 2-26, Cerdanyola del Vallés, Barcelona 08290, Spain.
authors.forename: Lucía
authors.initials: L
authors.lastname: Aballe
authors.affiliation: ALBA Synchrotron Light Facility, Carrer de la Llum 2-26, Cerdanyola del Vallés, Barcelona 08290, Spain.
authors.forename: Michael
authors.initials: M
authors.lastname: Foerster
authors.affiliation: Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands.
authors.forename: Herre S J
authors.initials: HS
authors.lastname: van der Zant
authors.affiliation: Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid, Spain.|Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain.
authors.forename: Gabino
authors.initials: G
authors.lastname: Rubio-Bollinger
authors.affiliation: Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid, Spain.|Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Campus de Cantoblanco, E-28049 Madrid, Spain.|Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain.
authors.forename: Nicolás
authors.initials: N
authors.lastname: Agraït
authors.affiliation: Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid, Spain.
authors.forename: J J
authors.initials: JJ
authors.lastname: Palacios
authors.affiliation: Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Campus de Cantoblanco, E-28049 Madrid, Spain.
authors.forename: Emilio M
authors.initials: EM
authors.lastname: Pérez
authors.affiliation: Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Campus de Cantoblanco, E-28049 Madrid, Spain.
authors.forename: Andres
authors.initials: A
authors.lastname: Castellanos-Gomez