10/11/2023
Why does it get hot when you rub things together?
Friction, an everyday phenomenon, has perplexed scientists for centuries. Though extensively researched, our understanding remains fragmented, primarily due to the multifaceted interactions that span across varying scales. Achieving an accurate grasp of the precise contact conditions between objects has been a longstanding challenge, a feat recently made possible through advancements in scanning probe microscopy.
Yet, even with these technological breakthroughs, the intricacies of dynamic friction - the force needed to maintain the movement of a molecule - have remained elusive. While scientists could measure static friction by moving a single molecule on a surface, both the measurement and theoretical understanding of dynamic friction have yet to be fully unveiled.
Now, writing in Physical Review Letters and Physical Review B, a collaborative team from Kanazawa University (Japan), the Donostia International Physics Center (Spain), and the University of Regensburg (Prof. Dr. Franz J. Giessibl, Chair of Quantum Nanoscience) report their groundbreaking study that dives deep into this challenge. They meticulously examined the manipulation of a carbon monoxide (CO) molecule on a single-crystal copper surface using an atomic force microscope. Backed by ab initio calculations, their findings shed light on:
- How the CO molecule positions relative to the microscope tip and surface.
- The relationship between the motion of the molecule induced by the tip, energy dissipation, and both static and dynamic friction.
"Friction can ultimately be traced back to the forces of atomic contacts between two rubbing bodies. As a model, one can imagine an egg in an egg carton, whose depressions represent the preferred places of an atom "rubbing" on it. However, the forces acting between atoms do not have such a simple nature as the forces to which an egg in an egg carton is subject. Rather, the nature of these forces is governed by quantum mechanics, and not by the simpler and much older classical mechanics. Professor Okabayashi and his colleagues have now found that when a carbon monoxide molecule is pushed across a metal surface, a mysterious bridge state is formed that can only be described by quantum mechanical calculations", explains Prof. Dr. Giessibl.
This research stands out for its unequivocal clarity on the friction process. Not only does it provide fresh insights into a long-studied phenomenon, but it also paves the way for future studies on energy dissipation relaxation processes.
Source: University of Regensburg