| dc.description.abstract | Here we propose a design to optimise measurement of the transverse spin voltage resulting from the spin Hall effect (SHE) generated by shining circularly polarised light on a transition metal dichalcogenide (TMD) monolayer. There is currently a lot of interest in trying to create ohmic contacts to single layer TMDs due to the inherent Schottky barriers present at the metal to semiconductor interface, but the more successful methods either cover the entire flake or rely on a temporary doping with a low half-life. We propose using graphene as an intermediary contact with top gates only over the contacted regions leaving a central area of the TMD flake exposed so that the laser can reach it unimpeded. To maximise the SHE, the strength of the spin-orbit coupling of the atmospherically-stable TMDs have been reviewed. Armed with this information, and given that WSe$_2$ is an intrinsically p-type TMD, it was found to be the best candidate for investigating the SHE in such two-dimensional materials.
We have successfully both exfoliated and used Raman spectroscopy to characterise graphene and TMD flakes, using photoluminescence (PL) spectroscopy for the characterisation of the latter as well: whereas Raman spectroscopy has proven to be very effective in determining the layer number of the graphene and WSe$_2$ flakes, in the case of MoS$_2$, PL spectra can be more definitive in distinguishing monolayer from multilayer flakes. We unexpectedly, as WSe$_2$ is thought to be atmospherically stable, observed a change in the visibility of WSe$_2$ over a matter of four weeks, even when stored in a vacuum. The corresponding PL spectrum was also found to be heavily suppressed. Here we also report out attempts at stacking graphene onto TMD flakes to produce ohmic contacts. | en_GB |
