Friction on I‐Modified Au(111) in a Tetraglyme Electrolyte

Abstract

AbstractIn situ electrochemical lateral force microscopy (EC‐LFM) has been employed to study the ordered structure of Li+ containing tetraglyme (G4) in front of I‐modified Au(111) and its influence on friction as function of normal load. Since the effect of water in aprotic electrolytes is a critical issue, the influence of water on the ordered structure and friction was also been investigated. Lateral force maps recorded at low normal load (FN<30 nN) show that the adsorbed iodine forms a structure ( independent of potential. With increasing normal load, observed atomic corrugations at both potentials (0.45 V and −0.4 V) are in agreement with the Au(111) ( structure while returning to a structure with decreasing normal load. Thus we conclude that the AFM tip penetrates into the iodine adlayer without irreversible wear. Astonishingly, no clear friction increase was observed upon penetration into the iodine adlayer; also no corresponding step was found in force separation (FS) curves. On the other hand, FS curves for I‐modified Au(111) in pure G4 solvent and Li+ containing electrolyte clearly showed several steps suggesting that G4 molecules are forming up to five ordered layers. It is noteworthy that we observed two different push‐through forces for the innermost layers. Considering the higher reproducibility of FS curves on I‐modified Au(111) compared to bare Au(111) we assume that the low surface energy of the iodine monolayer leads to negligible interaction between G4 molecules and iodine adlayer, resulting in less perturbations of the structure by the solid phase and also an increase of push‐through force. Charts of friction forces vs. normal load are found to be independent of applied potential and the concentration of water.