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.

Narrow-band anisotropic electronic structure of ReS2

“…Angle-dependent Raman scattering measurements of these samples show strong anisotropy in the 214 cm −1 peak intensity with clear twofold symmetry, as seen in recent reports [9,17,18].…”

Cleavage tendency of anisotropic two-dimensional materials:ReX2(X=S,Se) andWang1, Liu2, Wang3 et al. 2017Phys. Rev. B611470View full textAdd to dashboardCite

“…L. Hart et al [15] also found similar phenomenon that the crystallographic b-axis of ReS2 flakes frequently formed the longer edge of cleaved crystals, clearly indicating larger appearance probability for b-axis than a-axis. This study is in good agreement with our experiment results.…”

Advent of 2D Rhenium Disulfide (ReS2): Fundamentals to Applications

“…[16,25,61] Owing to its unusual atomic structure and assymetric crystal growth, ReS2 exhibits different fundamental properties from other TMDs. Here below we have reviewed such properties.…”

“…This distortion in crystal structure renders weak coupling between interlayers which can result in the bulk ReS2 behaving like electronically 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 and vibrationally decoupled monolayers. [16,20,64] This is a significant advantage over other TMDs which undergo a transition from indirect to direct bandgap semiconductor when reduced from bulk to monolayer. The resilient bandgap with no direct-indirect transition offers remarkable possibilities to produce relatively large-area ReS2 of a single molecular layer thickness.…”

“…Aside from the most popular TMDs of group VI, rhenium disulfide (ReS2, an example of group VII TMDs) has recently attracted significant interest for its wholly unusual properties in all aspects of structural, electro-optical and chemical properties. [16,17] Most notably, an indirect to direct transition is obvious for group VI-TMDs when thinned down to monolayer from the bulk material. [18,19] Whilst different to other TMDs, ReS2 has shown layer independent electrical, optical and vibrational properties.…”