Intercalated water-induced hysteretic friction behavior of graphene, h-BN, and MoS2

Two-dimensional (2D) materials have extraordinary properties that promise significant advancement of electronic, mechanical, and electrochemical devices. However, these properties are often measured in ideal, clean states, absent from contamination from their surrounding environment. Here we study the impact of water intercalation on the mechanical and lubricating properties on 2D nanofilms of graphene, h-BN, and MoS2 using atomic force microscopy (AFM) and molecular dynamics (MD) simulations. Comparing the performance of pristine 2D nanofilms and those with water intercalated between the substrate and the 2D nanofilm, we observed higher friction in intercalated samples than in pristine samples. In load dependent friction measurements, we also observed that the friction hysteresis varied from pristine samples to those with water intercalated. MD simulations suggest that this difference was a result of a decrease in the apparent out -of-plane mechanical stiffness of the 2D nanofilm and a reduction in the adhesive interaction between substrate and nanofilm that occurred when water was intercalated between the 2D material and the substrate, allowing for a change in the out-of-plane deformation behavior of the supported 2D nanomaterial. These observations suggest that 2D materials experience performance degradation when exposed to ambient conditions.