Influence of interface hydration on sliding of graphene and molybdenum-disulfide single-layers

Abstract Humidity influences friction in layered materials in peculiar ways. For example, while water improves the lubricating properties of graphite, it deteriorates those of molybdenum disulfide (MoS 2 ). The reasons remain debated, not the least due to the difficulty in experimentally comparing dry and hydrated interface frictions. Here we show that the hydration of interfaces between a mica substrate and single-layers of graphene and MoS 2 with a molecularly thin water layer affects strain transfer from the substrate to the 2D materials. For this, we strain the substrate and detect strain in graphene and MoS 2 by changes in Raman and photoluminescence spectra, respectively. Strain relaxation in graphene changes from stick-slip in dry contact, to viscous when hydrated. In contrast, there is no viscous relaxation in MoS 2 regardless of hydration. Our work provides a novel approach for better understanding the impact of hydration on friction in layered materials.