Monolayers in a Scanning Tunneling Microscope (STM)

The use of two-dimensional materials has grown throughout the years as we push to study systems that are in the micro- and nanoscales. When the thickness of these materials is reduced down to a single atomic layer, we can take advantage of the properties of these transition metal dichalcogenides (TMDs) such as the indirect-to-direct band gap transitions in order to induce luminescence from optical fields. Here, we study the luminescence emission from a monolayer of MoSe₂ on a gold (Au) substrate using STM. More specifically, we use a theoretical point of view to understand the possibility of plasmon-exciton hybridization within the gap region that may lead to light emission through electrodynamic simulations. We compute near-field intensity spatial distributions using the finite-difference time-domain method (FDTD) to study the coupling mechanism between the MoSe₂ monolayer and Au substrate. With our computational model, we observe that there is a significant increase in local-field intensity within the MoSe₂ monolayer with respect to the local-field generated in the Au tip- Au surface junction. This significant local-field enhancement in the MoSe₂ mediates an effective plasmon-exciton coupling. Computational results are compared and discussed with experimental results.