Creating a Nanoscale Lateral Heterojunction in a TMD Monolayer by Engineering the Electrostatic Landscape

As technology has advanced, the rush to miniaturization has led to the ultimate limit of<br/>atomically thin, two dimensional (2D) materials. Within this family of materials, the emergence<br/>of atomically thin semiconducting transition metal dichalcogenides (TMDs) has provided<br/>exciting possibilities for advanced 2D electronics, including devices comprised of a single<br/>atomic layer. However, future technology based on TMDs hinges on the capability of creating<br/>nanoscale lateral junctions with large built-in potentials. Following the paradigm of three-<br/>dimensional counterparts, lateral heterojunctions have been directly synthesized by stitching two<br/>different TMD monolayers together, but this approach considerably constrains the attainable<br/>band offsets. However, the extreme 2D nature of TMDs provides other opportunities to<br/>manipulate their electronic properties, as their quasiparticle band gap is not static and depends<br/>strongly on the proximal environment. Recent studies have shown this effect can be harnessed to<br/>engineer a lateral heterojunction in monolayer TMDs by controlling the proximal environment<br/>through substrates, capping layers, and adsorbates. 1, 2, 3, 4 Here we demonstrate the creation of a<br/>nanoscale lateral heterojunction in monolayer MoSe 2 by intercalating Se at the interface of a<br/>hBN/Ru(0001) substrate. The Se intercalation modulates the local hBN/Ru work function, and<br/>this sudden change in the local electrostatic environment is imprinted directly onto monolayer<br/>MoSe 2 to create a large built-in potential of ~0.8 eV. We spatially resolve the MoSe 2 band profile<br/>and work function using scanning tunneling spectroscopy to map out the nanoscale depletion<br/>region. The Se intercalation also modifies the dielectric environment, influencing the local band<br/>gap renormalization and increasing the MoSe 2 band gap by ~0.23 eV. This work illustrates that<br/>environmental proximity engineering provides a robust method to indirectly manipulate the band<br/>profile of 2D materials outsidethe limits of their intrinsic properties, opening alternative avenues for device design.<br/><br/>1. M. Utama et. al., Nat. Electron., 2 (2019) 60-65.<br/>2. J.-W. Chen et. al., Nat. Comm., 9 (2018) 3143.<br/>3. A. Raja et. al., Nat. Comm., 8 (2017) 15251.<br/>4. Z. Song et.al, ACS Nano, 11 (2017) 9128-9135.