Atom-by-atom engineering of impurity energy levels on a semiconductor surface

Defects in transition metal dichalcogenides (TMDs) exhibit electronic and optical properties that make them promising candidates for use as single photon emitters and in quantum spin memory architectures, among many other applications. While some TMD defects are predicted to host localized in-gap states, in practice they can be difficult to identify or engineer for desired functionalities. In this talk, we show how deep in-gap states can be engineered by adsorbing charged atomic adatoms onto the surface of WSe₂.The weak dielectric environment of the WSe₂ surface promotes the formation of deep potential wells that confine quasiparticles, leading to discrete hydrogenic-like energy levels. We use scanning probe microscopy both to measure the shape of the potential well that forms around the adatoms and to image the spatial structure and energies of the resulting bound states. Using the scanning probe tip, we deterministically placed the adatoms into clusters of increasing size, creating deeper potential wells and new bound state energy levels. We compare these results to energy levels predicted by density functional theory and tight-binding calculations to assign spectroscopic features to hydrogenic-like energy levels.