Probing tribological evolution in atomically thin MoS₂ at different scales

Area of Science:

• Nanotribology
• Materials Science
• Surface Science

Background:

• Atomic-scale stick-slip motion and nanoscale strengthening are key in 2D material nanotribology.
• Sub-nanoscale origins and load-dependent evolution of these phenomena require further investigation.

Purpose of the Study:

• To systematically investigate sub-nanoscale friction and strengthening effects in atomically thin molybdenum disulfide (MoS₂) under controlled loads.
• To quantify the load-dependent evolution of nanoscale strengthening and sub-nanoscale stick-slip motion.
• To elucidate the underlying mechanisms governing these tribological behaviors.

Main Methods:

• Utilized a calibrated atomic force microscope (AFM) to perform systematic friction measurements on MoS₂.
• Controlled applied load and MoS₂ layer thickness during experiments.
• Quantified slip distance as a metric for sub-nanoscale stick-slip motion.

Main Results:

• Nanoscale strengthening intensifies with increasing load but weakens with more MoS₂ layers.
• Slip distance, a metric for stick-slip motion, transitions from constant to increasing, then decreasing with load.
• Load-dependent transitions in friction are governed by competing mechanisms: contact quality, puckering effect, and static friction.

Conclusions:

• Sub-nanoscale stick-slip motion and strengthening in MoS₂ are critically dependent on applied load and layer thickness.
• Understanding these load-dependent transitions provides insights for designing low-friction coatings.
• Findings advance 2D material tribology to the sub-nanoscale, crucial for micro/nanoelectromechanical systems (MEMS/NEMS).