Dual-Peak Friction Upon Traversing a Monolithic Subsurface Step in Layered Materials

High-resolution atomic force microscopy (AFM) measurements reveal a distinctive anomalous dual-peak feature emerges in friction force when the tip scans across a well-defined monolithic step covered by few-layer 2D materials, deviating fundamentally from the conventional single-peak expected for a simple topographic obstacle. Through systematic high-resolution stick-slip measurements, nanoindentation experiments, and molecular dynamics (MD) simulations, this bifurcated frictional response is attributed to the asynchronous evolution of the resistive and driving force as the tip becomes transiently pinned first at the front and then at the rear of the step. The dual-peak friction mechanism provides new perspectives for addressing inevitable step-related challenges in 2D material lubrication systems, which is essential for elucidating the frictional origins of structural superlubricity in devices.