Substrate deformability and applied normal force are coupled to change nanoscale friction

Area of Science:

• Tribology
• Nanomechanics
• Materials Science

Background:

• Amonton's law describes friction as proportional to normal force, with a constant friction coefficient.
• This classical model may not fully capture nanoscale friction phenomena.
• Understanding nanoscale friction is crucial for designing advanced materials and devices.

Purpose of the Study:

• To investigate nanoscale kinetic friction between an AFM tip and graphene.
• To explore deviations from Amonton's law under varying normal forces and substrate deformability.
• To elucidate the underlying mechanisms driving friction behavior changes.

Main Methods:

• Molecular dynamics simulations were employed to model the nanoscale system.
• Simulations analyzed the interplay between normal force and substrate deformability.
• The Prandtl-Tomlinson model was used to interpret energy landscape changes.

Main Results:

• Friction behavior deviates from Amonton's law at the nanoscale.
• Substrate deformation influences friction, lowering it at low loads and increasing it at high loads.
• A transition from stick-slip to paired stick-slip friction was observed above a critical force threshold.

Conclusions:

• Nanoscale friction is complex, influenced by normal force and substrate properties.
• Changes in microscopic contact states and energy landscapes drive friction behavior.
• The findings provide insights into nanoscale tribological mechanisms.