Sliding Friction in Liquid Environments at the Nanoscale

Friction Force Microscopy (FFM) conducted in liquid environment proves to be a highly effective method for investigating atomic-scale friction on crystalline surfaces. It can probe friction between surface atoms while also providing sublattice resolution, opening doors to new areas of research. The observed similarity in FFM measurements conducted in liquid environments and Ultra-High Vacuum (UHV) is attributed to the lack of capillary bridges in both settings. These bridges usually increase adhesion between the scanning probe and the sample, resulting in surface wear during imaging in ambient conditions. We review various instances of nanotribological phenomena occurring on crystalline surfaces within different liquid environments—specifically water, ethanol, and ionic liquids—as studied by the authors of this chapter. We discuss the influence of the damping state of the sliding contact in the presence of liquids, which is reflected by variations in the slip length of the scanning probe. Finally, we showcase how FFM can be used to investigate sliding friction in ionic liquids. This approach allows us to probe the fascinating interplay between friction at the nanoscale and the unique nanostructures formed by confined ionic liquids.