Single-layer MoS2 roughness and sliding friction quenching by interaction with atomically flat substrates

TL;DR

This study investigates how different substrates affect the surface roughness and friction of single-layer MoS2, revealing that atomically flat h-BN substrates best preserve flatness and reduce friction, with implications for nanoscale device performance.

Contribution

It provides experimental evidence on substrate-dependent roughness and friction in single-layer MoS2, highlighting the role of substrate material in surface quality and tribological properties.

Findings

h-BN substrate best preserves MoS2 flatness

Friction decreases with reduced roughness on different substrates

Bulk MoS2 surface exhibits lower friction than single-layer flakes

Abstract

We experimentally study the surface roughness and the lateral friction force in single-layer MoS2 crystals deposited on different substrates: SiO2, mica and hexagonal boron nitride (h-BN). Roughness and sliding friction measurements are performed by atomic force microscopy (AFM). We find a strong dependence of the MoS2 roughness on the underlying substrate material, being h-BN the substrate which better preserves the flatness of the MoS2 crystal. The lateral friction also lowers as the roughness decreases, and attains its lowest value for MoS2 flakes on h-BN substrates. However, it is still higher than for the surface of a bulk MoS2 crystal, which we attribute to the deformation of the flake due to competing tip-to-flake and flake-to-substrate interactions.