Superlubricity between MoS₂ Monolayers

Abstract

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.