Defects Induced in 1T-TaS₂ and Mott Gap Modification by Oxygen Dosing.

Defects can impact the electronic and optical properties of transition metal dichalcogenides (TMDs) and oxygen induced defects are of particular importance because a subset of TMDs degrade in air by reacting with oxygen. Here we report our observations of defects induced in 1T −TaS₂ after controlled oxygen exposure in ultra high vacuum (UHV). 1T − TaS₂ was exfoliated in UHV, and high resolution scanning tunneling microscopy (STM) and spectroscopy (STS) were used to study changes in topography and band structure due to oxygen dosing. 1T − TaS₂ surface topographs at T = 10K show defects of varying shapes and sizes after a 10⁻⁵torr dose of O₂ for 1 minute. The spatial distribution of these defects is nonuniform across 1T − TaS₂ surface. The STS data on defect sites shows shifts in the local density of states (LDOS) peak positions, which indicate a local modification of the Mott gap. We propose that these changes in the lower and upper Hubbard bands of this strongly correlated system are induced due to the substitution of oxygen at sulfur vacancies. These findings support the mechanism by which oxygen induced defects in TMDs can modify the local electronic structure, potentially affecting emergent phenomena in 2D materials and are especially important for air-sensitive TMDs.