title: Rhenium Dichalcogenides: Layered Semiconductors with Two Vertical Orientations.
abstract: The rhenium and technetium diselenides and disulfides are van der Waals layered semiconductors in some respects similar to more well-known transition metal dichalcogenides (TMD) such as molybdenum sulfide. However, their symmetry is lower, consisting only of an inversion center, so that turning a layer upside-down (that is, applying a C2 rotation about an in-plane axis) is not a symmetry operation, but reverses the sign of the angle between the two nonequivalent in-plane crystallographic axes. A given layer thus can be placed on a substrate in two symmetrically nonequivalent (but energetically similar) ways. This has consequences for the exploitation of the anisotropic properties of these materials in TMD heterostructures and is expected to lead to a new source of domain structure in large-area layer growth. We produced few-layer ReS2 and ReSe2 samples with controlled "up" or "down" orientations by micromechanical cleavage and we show how polarized Raman microscopy can be used to distinguish these two orientations, thus establishing Raman as an essential tool for the characterization of large-area layers.
authors.affiliation: Department of Physics, University of Bath , Bath BA2 7AY, United Kingdom.
authors.forename: Lewis
authors.initials: L
authors.lastname: Hart
authors.affiliation: Department of Physics, University of Bath , Bath BA2 7AY, United Kingdom.
authors.forename: Sara
authors.initials: S
authors.lastname: Dale
authors.affiliation: Department of Physics, University of Bath , Bath BA2 7AY, United Kingdom.
authors.forename: Sarah
authors.initials: S
authors.lastname: Hoye
authors.affiliation: Department of Physics, University of Bath , Bath BA2 7AY, United Kingdom.
authors.forename: James L
authors.initials: JL
authors.lastname: Webb
authors.affiliation: Department of Physics, University of Bath , Bath BA2 7AY, United Kingdom.
authors.forename: Daniel
authors.initials: D
authors.lastname: Wolverson
mesh_terms: D018360:Crystallography, X-Ray; D008982:Molybdenum / Q000737:chemistry; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D012211:Rhenium / Q000737:chemistry*; D012666:Semiconductors; D028561:Transition Elements / Q000737:chemistry*
chemical_list: D028561:Transition Elements; D012211:Rhenium; D008982:Molybdenum
keywords: MoS2; Raman spectroscopy; ReS2; ReSe2; asymmetry; phonon; rhenium diselenide; rhenium disulfide; transition metal dichalcogenide