In situ imaging of shearing contacts in the surface forces apparatus

Multiple beam interferometry (MBI) can be used in the surface forces apparatus for in situ topographical imaging in real-time of the contact between two shearing surfaces at ultrahigh resolution in the normal direction at the same time as friction forces are measured. Simultaneous measurements were made of the friction forces between two shearing mica surfaces separated by WS2 (inorganic) fullerene, and non-fullerene WS2 nanoparticle additives in tetradecane. The results were correlated with the very different transfer layers formed in each case, as visualized by in situ MBI and ex situ atomic force microscopy.