Imaging the Electronic Structure of Magnetic and Non-Magnetic Atomic Impurities in Monolayer Semiconductors*

It has been predicted that a two dimensional dilute magnetic semiconductor (2D DMS) can be formed by suitably doping monolayer transition metal dichalcogenides with magnetic materials. Here we present scanning tunneling microscopy (STM) and spectroscopy (STS) data on these doped monolayers. We identify and characterize multiple impurity types resulting from the doping procedure, observing both magnetic and non-magnetic impurities. Using a full spectral mapping in position and energy space, and through comparison to density functional theory calculations, we can associate these impurity states with different impurity types and incorporation sites. For example, we have found transition metal substitutional dopants and a dichalcogenide substitutional dopant. Specific dopant arrangements demonstrate strong spin splitting, a necessary ingredient towards achieving a 2D DMS state in monolayer semiconductors.