Striped nanoscale friction and edge rigidity of MoS2 layers

Abstract

Lateral force microscopy (LFM) is used to probe the nanoscale elastic and frictional characteristics of molybdenum disulfide (MoS₂). We find that MoS₂ edges are effectively flexed over a region of about 10 nm when scanned with sharp single asperity LFM probes, with energies consistent with out-of-plane bending and being slightly stiffer than those of graphene. Additionally, we report the first observation of a striped nanoscale frictional phase on the surface of MoS₂. This frictional phase is fixed to the underlying MoS₂ with a modulation length of ∼4 nm that is insensitive to scan parameters and has domain sizes that exceed 100 nm. The amplitude of these features is found to be relatively independent of the geometry of the tip asperity and the applied load within the ranges we investigate. Experimental results suggest this periodic friction can be explained by variations in the local strain in the underlying MoS₂. These results could have general applicability to understanding the nanomechanical properties of the growing array of laminar materials that are of potential use as atomically-thin coatings to future nanoscale machines.