Unveiling surface and subsurface atomic vacancies in MoS₂ with lateral force microscopy.

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• Atomic-scale defects critically influence material properties, especially in low-dimensional systems.
• Accurate identification and localization of these defects are crucial for scientific advancement and technological innovation.
• Lateral Force Microscopy (LFM), typically sensitive only to surface layers, has not been used for subsurface defect analysis.

Purpose of the Study:

• To demonstrate that LFM can detect and classify atomic vacancies based on their depth within Molybdenum Disulfide (MoS2).
• To establish unique frictional signatures for surface versus subsurface vacancies.
• To generalize the findings beyond MoS2 using a physical model.

Main Methods:

• Experimental investigation using Lateral Force Microscopy (LFM).
• Computational validation through molecular dynamics simulations.
• Theoretical modeling using the Prandtl-Tomlinson (PT) model to understand the underlying friction mechanism.

Main Results:

• LFM successfully differentiated between surface and subsurface atomic vacancies in MoS2.
• Surface vacancies exhibited a 'drop-and-rise' friction signature, while subsurface vacancies showed a distinct exit barrier without an initial drop.
• The PT model confirmed a generic lattice disruption mechanism, indicating broader applicability of the LFM technique for defect analysis.

Conclusions:

• LFM is a powerful technique for probing and classifying atomic defects by depth, challenging previous assumptions about its surface sensitivity.
• The identified frictional fingerprints provide a new method for defect characterization in 2D materials.
• The study enables comparative analysis of defect types and densities in MoS2 produced by different methods like chemical vapor deposition (CVD) and mechanical exfoliation.