Superlubricity between MoS2 Monolayers.

The ultralow friction between atomic layers of hexagonal MoS2 , an important solid lubricant and additive of lubricating oil, is thought to be responsible for its excellent lubricating performances. However, the quantitative frictional properties between MoS2 atomic layers have not been directly tested in experiments due to the lack of conventional tools to characterize the frictional properties between 2D atomic layers. Herein, a versatile method for studying the frictional properties between atomic-layered materials is developed by combining the in situ scanning electron microscope technique with a Si nanowire force sensor, and the friction tests on the sliding between atomic-layered materials down to monolayers are reported. The friction tests on the sliding between incommensurate MoS2 monolayers give a friction coefficient of ≈10-4 in the regime of superlubricity. The results provide the first direct experimental evidence for superlubricity between MoS2 atomic layers and open a new route to investigate frictional properties of broad 2D materials.