A Unified Understanding of Nanoscale Friction for Common van der Waals Materials

Abstract

Many fascinating properties and applications of van der Waals (vdW) materials arise from how their layers slide against each other. Quantifying friction at the nanoscale is essential for further advancing the assembling of sophisticated heterostructures and their applications. A unified model and experimental validation for such friction forces remain elusive. A simple linear relationship between friction force and the energy barrier encountered by an atomic force microscope (AFM) tip interacting with crystal atoms has been proposed but not experimentally validated. Here, we present a unified understanding of nanoscale friction in vdW materials through lateral force microscopy measurements using a single AFM tip on four commonly studied vdW materials: MoS2, MoSe2, WS2, and graphene. Remarkably, the measured friction not only follows a proportional relationship with respect to the energy barriers calculated using the Lennard-Jones potential but agrees with predicted values within 5% across all examined materials. This agreement is achieved by accounting for variations in the number of contact-edge tip atoms that likely settle simultaneously into hollow sites in each material. Our findings provide critical insights to support a wide range of research efforts that rely on an advanced understanding of nanotribology in vdW materials.