Tunable friction of monolayer MoS2 by control of interfacial chemistry

In this report, we utilize the heterostructures of monolayer MoS2 and self-assembled monolayers (SAMs) of organic molecules as a platform to understand how carrier density of nanomaterials affects their friction behaviors. Previous studies on the friction of two-dimensional materials have explored the effect of lattice structures and morphologies. Given the same normal force and scanning speed of the AFM tip, we observe the sliding friction of high-quality n-type monolayer MoS2 could be reduced by SAMs. The friction tunability is attributed to the charge transfer from MoS2to SAMs, which modulated the carrier density and hence the carrier-mediated friction behaviors in 2D MoS2. ab initio simulations and nanoscale mapping of work functions support this hypothesis. These SAMs-based heterostructures provide a potential tool to control friction in low-dimensional materials, and also an original perspective on the effect of electron–phonon coupling on friction at nanoscale.