In-situ Observation of Shear Deformation of Gold Single Real Contact Point at the Nanoscale

We in-situ observed the deformation of a gold single real contact point at the nanoscale during friction experiment in order to reveal the mechanism of friction. In this experiment, a special experimental setup combining between micro-electro-mechanical system (MEMS) and transmission electron microscope (TEM), called MEMS-in-TEM, was utilized for the stable visualization of the real contact point. Gold tips with electrostatic actuators were gently brought into contact and were rubbed each other at a quasi-static speed under TEM observation. Between tips, the gold single real contact point was formed and deformed in shear. During this deformation, the ends of the real contact point travelled 2.8 nm along the surface of the gold tips, although those of silicon and silver did not move. The maximum friction was 60 nN, repeating the stick-slip behavior from 35 to 60 nN. This result will be helpful to understand the mechanism of friction at the nanoscale and the lubrication mechanism of solid lubricants.