Intrinsic properties of 2D transition metal dichalcogenide (TMD) semiconductors are highly sensitive to the presence of defects in the crystal structure. Understanding the defect electronic structure at the atomic scale will enable unprecedented control over material functionality.

In this talk I will present two different examples of structural defects on single layers of MoSe₂. Using low temperature (4K) Scanning Tunneling Microscopy and Non-Contact Atomic Force Microscopy we visualize and correlate in 2D MoSe₂ the morphology and electronic properties of structural defects with atomic resolution. We find how individual Se vacancies form atomically confined Type I hetero junctions with the surrounding pristine MoSe₂. We also identified linear defects in form of Mirror Twin Boundaries in MoSe₂, which form 1D metal channels embedded in the surrounding semiconductor. At low temperatures these 1D metallic states open a band gap at the Fermi level of 100 meV together with periodic beatings in the local density of states, both characteristic of charge density waves.