Carbon-related nanometer-scale defects on MoS2 revealed by scanning tunneling microscopy

초록

We present a scanning tunneling microscopy (STM) study of nanometer-scale surface defects on the 2H-MoS2(0001) surface of a natural single-crystal mineral. Two dominant types of nanometer-scale defects, denoted as B and D, were ubiquitously observed on freshly exfoliated surfaces in both ultra-high vacuum and ambient environments as well as on intentionally carbon-deposited surfaces. All these observations exclude an extrinsic adsorption-related origin and instead suggest a carbon-related bulk source. The B defects exhibit a pronounced bias-dependent contrast reversal, appearing as bright protrusions at negative sample biases and as dark depressions at positive biases. In contrast, the D defects appear consistently as dark depressions over the entire bias range. The defect population increases gradually over time, supporting an intrinsic bulk reservoir of carbon species. In addition, reversible interconversion between the B and D defects is observed during STM scanning, suggesting that they originate from the same defect species occupying closely related adsorption configurations with similar energies. These results identify carbon impurities as the origin of the most prevalent nanometer-scale surface defects on MoS2 and establish a consistent framework for interpreting their STM contrast and evolution.

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