Friction on the micro-scale depends on surface orientation


Friction between two objects can be understood by the making, stretching, and breaking of thousands of atomic-scale asperities. We achieved to measure the friction forces with atomic resolution using atomic force microscope. Our measurements showed that the friction is dependent on the relative orientation of the atomic structure of surfaces in the contact. The performed calculations provided a deeper understanding of the origin of the directional dependence of the friction as a result of different excitation of vibrational modes at the surface. 

Results of an experiment (topography and plots related to lateral force detection) show lateral forces measured either in directions perpendicular (on the left) and parallel (on the right) to the silicon dimers. Ball-and-stick atomic models of the surface are added for reference (yellow balls represent silicon, white balls hydrogen). Lateral forces measured during scans along the blue or red line shown the corresponding topography image are plotted in the lower part of the figure; solid lines shows the experimental results while the dots correspond to simulations.