2019 Volume 17 Pages 124-129
When the mean free paths of acoustic phonons are larger than half the MoS2 island size, the generated acoustic phonons remain at nonequilibrium and are confined within the island or form standing waves. In contrast, when the island size decreases to less than 1 μm, surface softening increases, reducing the barrier of the tip—surface interaction potential. Unexpectedly, the friction force from an island with a size of 0.2 μm abruptly decreases to below 10 pN. The superlubricity described here is a novel type involving phonon confinement and surface softening that is easily achievable and very simple because it uses only nanostructures smaller than 1 μm.