Observation of Nanoscale CDW domains in few-layer 1T-TaS₂

1T-TaS₂ exhibits a series of charge density wave (CDW) phases with decreasing temperature, finally forming a √13×√13 commensurate CDW below 180 K. Recent focus has been on understanding metastable CDW states formed by cooling rate, laser pulses, or voltage pulses. Scanning tunneling microscopy (STM) of these induced phases has shown nanoscale CDW domains, some of which are metallic, with many types of domain walls. We report observations of nanoscale domains of the commensurate CDW in thin flakes of mechanically exfoliated 1T-TaS₂ by STM at 10 K. Samples were prepared on doped Si substrates by robotic exfoliation in inert gloveboxes at the Quantum Material Press at Brookhaven National Laboratory and transferred to ultra-high vacuum after ~ 2 hours of exposure to air. Ex-situ atomic force microscopy (AFM) measurements showed flake thicknesses between 4 and 18 nm. Despite air exposure, large areas appeared clean in STM images. The domains show different electronic contrasts, and we identified 10 different types of domain walls. Overall, the features are similar to the metallic mosaic hidden phase that was induced by laser or voltage pulses in bulk crystals. This work provides an example of the observation of the metallic mosaic phase without stimulation. It also raises questions about the role of air exposure on the exfoliated flake surface.