Impact of Oxygen Defects on the Electronic Properties and Stability of 1T-TaS₂

A subset of transition metal dichalcogenides (TMDs) are not stable in air: they react with oxygen and water causing degradation of their surfaces. The same materials host interesting physical behaviors, including charge density wave and superconducting phases. The air instability presents a challenge for creating high quality samples of 2D materials and heterostructures and accessing innate physical phenomena. To better understand the mechanism and impact of oxygen exposure on TMDs, we performed controlled oxygen dosing experiments on 1T-TaS2 in ultrahigh vacuum conditions and studied the induced defects by scanning tunneling microscopy and spectroscopy. We find the oxygen defects create states in the charge density wave gap and disrupt the electronic structure around the defect in a region several nanometers wide. Additionally, we find that with oxygen present, we can stimulate layer-by-layer surface degradation by extended imaging with a sample-tip bias between 1-3V. These results provide insight into the impact of oxygen defects on electronic properties of 1T-TaS2 and the atomistic surface chemistry of degradation.