Deciphering origin of nonmonotonic temperature-dependent sliding friction

• Revealing the phononic origin of non-monotonic temperature-dependent friction. • Thermal lubrication vs. collision cause friction trough at critical temperature. • Low-T thermal excitation generates small phonons aiding tip barrier crossing. • High-T excitation increases phonons , inducing atomic collisions and higher barriers. • Friction trough shifts to higher T with load/velocity via enhanced atomic nesting. This article systematically investigates origin of non-monotonic temperature-dependent friction, characterized by initial decrease and then subsequent rise, forming a friction trough. At low temperatures, thermal excitation generates a small number of phonons which facilitate tip crossing over potential barriers and thus reduce relative barriers and overall friction. However, at high temperatures, increased thermal excitation leads to more phonons which causes atoms on contact surfaces to collide and form higher interface barriers, resulting in greater friction energy dissipation. Further analysis shows that as normal load or sliding velocity increases, position of the friction trough shifts towards higher temperatures due to enhanced nesting degree of interface atoms, which requires more phonons generated at higher temperatures for assisting tip crossing over larger barriers.