Mapping the Electronic Structure of Two-Dimensional WS$_{\mathrm{2}}$ Heterostructures with Spatially Resolved ARPES at the MAESTRO Facility

Single-layer (SL) semiconducting transition metal dichalcogenides (TMDCs) such as WS$_{\mathrm{2}}$ exhibit strong spin-orbit coupling around the valence band maximum and a direct band gap that is highly sensitive to the dielectric properties of the surrounding medium. High-resolution angle-resolved photoemission spectroscopy (ARPES) studies of these properties are lacking for TMDCs on truly insulating supports such as oxides or hexagonal boron nitride (hBN), which form the basis of a wide range of high performance two-dimensional (2D) heterostructure devices. Here, we use the new microARPES capability with spatial resolution on the order of 10 $\mu $m at the MAESTRO facility at the Advanced Light Source (ALS) to spatially map the electronic structure of micron-sized SL WS$_{\mathrm{2}}$ heterostructures with transition metal oxides and hBN. We directly observe dramatic changes in the SL WS$_{\mathrm{2}}$ band structure and the gap around the valence band maximum when we vary the substrate or the charge carrier concentration in WS$_{\mathrm{2}}$. These findings are discussed in relation to how we can achieve control of the spin and optical properties of such 2D materials.