Local Electronic Properties of Coherent Single-Layer WS/WSe Lateral Heterostructures.

Lateral single-layer transition metal dichalcogenide (TMD) heterostructures are promising building blocks for future ultrathin devices. Recent advances in the growth of coherent heterostructures have improved the structural precision of lateral heterojunctions, but an understanding of the electronic effects of the chemical transition at the interface and associated strain is lacking. Here we present a scanning tunneling microscopy study of single-layer coherent TMD heterostructures with nearly uniform strain on each side of the heterojunction interface. We have characterized the local topography and electronic structure of single-layer WS/WSe heterojunctions exhibiting ultrasharp coherent interfaces. Uniform built-in strain on each side of the interface arising from lattice mismatch results in a reduction of the bandgap of WS. By mapping the tunneling differential conductance across the interface, we find type-II band alignment and an ultranarrow electronic transition region only ∼3 nm in width that arises from wave function mixing between the two materials.