Friction Coefficient Measured on a Single \[\mathbf{WS}_\mathbf{2}\] Nanoparticle: An In Situ Transmission Electron Microscope Experiment

An in situ friction test was carried out on a single \[\hbox {WS}_{2}\] nanoparticle in a transmission electron microscope (TEM) using a nanoindentation device able to measure normal and lateral forces independently. For the first time, quantitative results are reported: friction forces were recorded during the test, and thus, friction coefficient values were calculated. The exfoliation of the particle was observed during the experiment, and it was linked to the friction coefficient modification. The success of using this technique opens many possibilities of doing in situ friction tests in a TEM, especially for revealing and studying lubrication mechanisms.