Superlubricity under ultrahigh contact pressure enabled by self-assembled fluorinated azobenzene layers

Abstract Extensive efforts have been made to pursue an ultralow-friction state, which is known as superlubricity, with promising applications in many fields, such as mechanical and biomedical engineering. The load capacity of superlubricity has been considered to be crucial for industrial applications. Here, we report superlubricity under ultrahigh contact pressure by building a novel self-assembled fluorinated azobenzene layer on an atomically smooth highly oriented pyrolytic graphite (HOPG) surface. Sliding friction coefficients could be as low as 0.0005 or even lower under a contact pressure of up to 4 GPa. This ultralow-friction is attributed to molecular fluorination, which significantly weakens the intermolecular force between the close-packed fluorine atoms arrayed between the HOPG surface and the silicon atomic force microscopy (AFM) probe. This work provides a new approach to solid superlubricity under relatively high contact pressure, which might has great potential application value in the future.