Sliding friction over individual aromatic bonds correlates with bond order

Friction is ubiquitous, and has therefore been studied extensively to determine how it can be modified. Most experiments are not controlled down to the atomic level and encounter challenges with repeatability. We oscillate a tip ending in a single atom laterally over individual chemical bonds and measure the resulting energy dissipation. While one might expect the energy loss over aromatic bonds to be very similar, this is not the case. DFT-based simulations show that over aromatic bonds, the sliding friction correlates to bond order and is largely determined by the increased electron density between the atoms. Finally, we compare this to friction over hydrogen bonds and show that friction can be of the same magnitude but is due to interaction of the single atom asperity with the atoms of the hydrogen bond themselves. These findings show how friction can be tuned by adjusting the bond order of sliding surfaces.