Figure 1
From: Phase Modulators Based on High Mobility Ambipolar ReSe2 Field-Effect Transistors
(a) Scanning transmission electron microscopy (STEM) image of an exfoliated ReSe2 single-crystal displaying a chain-like atomic arrangement. (b) Electron diffraction pattern for a ReSe2 single-crystal when the incident electron-beam is perpendicular to the planar atomic arrangement showing a rectangular planar Brillouin zone. (c) Micrograph of a typical few layered ReSe2 single-crystal exfoliated onto SiO2 which from AFM (inset) had a step height of 2.7 nm, or was four layers thick (for an inter-planar lattice separation c = 0.6702 nm5). (d) Micrograph of the same crystal after deposition of the electrical contacts which consisted of 50 nm of Au on a 5 nm layer of Cr. The larger electrical contacts were used to source (S) and drain (D) the current Ids when performing two-terminal measurements. The smaller contacts V1 and V2 were used for voltage sensing in four-terminal measurements. For this sample, the separation between the current leads was L \(\cong \) 10.5 μm, the width of the channel was w \(\cong \) 3.6 μm and the separation between voltage leads was l \(\cong \) 4.5 μm. (e) Raman spectra of a ReSe2 monolayer. Given that inversion symmetry was the only symmetry operation present in the monolayer, in few-layers and in the bulk, there was just one Raman active irreducible representation, i.e. Ag. Therefore, all peaks were associated with Raman Ag modes. (f) Raman spectra for a crystal composed of five atomic layers. (g) Theoretical Raman spectra for monolayer (red) and bulk (blue) ReSe2.
