Atomic identification via the Prandtl-Tomlinson stick-slip mechanism
Distinguishing atomic species is an ongoing challenge in the field of scanning probe microscopy. Typically, atomic force microscopy makes use of electrostatic interactions to perform atomic identification. Here we perform lateral force microscopy (LFM) measurements with a CO terminated tip of a partially oxidized Cu(110) surface and show clear differences between the metal and oxygen sites over a large z-range. This allows for atomic identification on a typical metal oxide. Density functional theory based calculations show that the tip-sample interaction is dominated by short-ranged orbital interactions and that the electrostatic contribution is negligible. At small tip-sample distances, LFM can probe the Prandtl-Tomlinson stick-slip mechanism on the single-atom scale. It is visible as a striking asymmetry in the forward and backward scan directions, experimentally revealing this fundamental model for nanotribology on the single-atom scale.