Nonmonotonic Velocity Dependence of Atomic Friction Induced by Multiple Slips

Area of Science:

• Tribology
• Materials Science
• Surface Science

Background:

• Atomic-scale friction is crucial for understanding material wear and performance.
• The transition from single to multiple atomic slips is theoretically predicted but experimentally unverified as a function of velocity.
• Monolayer molybdenum disulfide (MoS2) on gold (Au(111)) serves as a model system for studying interfacial phenomena.

Purpose of the Study:

• To experimentally demonstrate and characterize the transition from single to multiple atomic slips.
• To investigate the effect of sliding velocity on atomic-scale friction in a MoS2/Au(111) system.
• To establish a velocity-corrugation phase diagram for atomic friction.

Main Methods:

• High-resolution friction force microscopy (HR-FFM) was employed to measure frictional forces at the atomic scale.
• Experiments were conducted on monolayer MoS2 grown on a Au(111) substrate.
• Computational modeling and simulations were used to interpret experimental results and explore the underlying mechanisms.

Main Results:

• A unique experimental signature of multiple atomic slips was identified as frictional velocity weakening.
• Friction was observed to decrease in a specific velocity interval (10-100 nm/s), contradicting conventional friction models.
• Model simulations reproduced the nonmonotonic frictional behavior, quantitatively agreeing with experimental data.

Conclusions:

• The study provides the first experimental evidence for velocity-dependent multiple atomic slips.
• The observed frictional velocity weakening is attributed to the complex interplay between velocity, surface corrugation, and slip dynamics.
• A generalizable velocity-corrugation phase diagram is proposed, offering a framework for understanding atomic-scale friction across different material systems.