Abstract
Several transitions in the friction coefficient with increasing load are found on Au(111) in sulfuric acid electrolyte containing Cu ions when a monolayer (or submonolayer) of Cu is adsorbed. At the corresponding normal loads, a transition to double or multiple slips in stick–slip friction is observed. The stick length in this case corresponds to multiples of the lattice distance of the adsorbed sulfate, which is adsorbed in a √3 × √7 superstructure on the copper monolayer. Stick–slip behaviour for the copper monolayer as well as for 2/3 coverage can be observed at FN ≥ 15 nN. At this normal load, a change from a small to a large friction coefficient occurs. This leads to the interpretation that the tip penetrates the electrochemical double layer at this point. At the potential (or point) of zero charge (pzc), stick–slip resolution persists at all normal forces investigated.
Highlights
Atomic-scale friction processes constitute a fascinating field of research which has been opened by the invention of the atomic force microscope (AFM) [1]
In [10,11] we investigated the effect of copper under potential deposition (UPD) on Au(111) and Pt(111) on friction and found an increase in friction force after adsorption of a sub- or monolayer of copper
In this paper we present the results of investigations of friction forces during UPD and dissolution of Cu/Au(111) and during sulfate adsorption in sulfuric acid solution
Summary
Atomic-scale friction processes constitute a fascinating field of research which has been opened by the invention of the atomic force microscope (AFM) [1]. The AFM allows us to determine the force necessary to move a cantilever tip laterally across the surface with atomic resolution. Tip atoms in contact with the surface remain at a certain surface position with a minimum of potential energy until the increasing lateral force initiates a slip toward the potential minimum. Many interesting aspects on the origin of friction and the underlying dissipative processes have been elucidated so far, but an overall understanding is still far from being complete [3,4,5,6].
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