Tip-Induced Etching and Vacancy Island Evolution on 2H-TaS₂ Revealed by STM

Recent research on 2D materials using scanning probe microscopy reveals that the surface of transition metal dichalcogenides can be etched during the measurement via either a tunneling-field-driven or a scanning probe-driven process. The tip-induced manipulation of the surface structure and defects is a first step toward nanolithography using scanning probes. Real-space scanning tunneling microscopy experiments provide a surface defect inventory, which includes linear and point defects for 2H-TaS₂ grown by chemical vapor transport. Extended periods of imaging trigger the formation of vacancy islands that grow and coalesce over time, leading to the sequential removal of entire layers. The growth kinetics of vacancies were observed over extended periods and quantified using AI and conventional image analysis tools. The vacancy islands have a linear growth rate of their perimeter and corresponding parabolic growth rates in the area for isolated islands. The growth rate variance of individual islands is discussed in the framework of etching mechanisms including tip-induced chemistry, etching by water adsorbates, and native defects that support vacancy island nucleation in the TaS₂ surface. New vacancy islands emerge rapidly in newly exposed layers after the top layer is removed. Small and mobile surface islands that are redeposited are revealed to participate in the tip-induced etching mechanism. The quantitative analysis of etching kinetics is a first step toward automated nanostructuring of TaS₂ surfaces. This work paves the way to use scanning tunneling microscopy to build more complex 2D material structures.