Mechanics-Guided Conformal Probes Enable Crystallographically Resolved Anisotropic Interlayer Friction Measurements in Low-Symmetry 2D Materials

Abstract

Interlayer sliding in two-dimensional (2D) materials is generally assumed to be weakly anisotropic, even as low-symmetry layered crystals with strongly direction-dependent properties continue to emerge. Here we adopt a mechanics-guided conformal probe design that enables quantitative measurement of crystallographically resolved interlayer friction between anisotropic 2D materials. Using Ta2NiSe5 as a model system, we demonstrate pronounced interlayer friction anisotropy approaching 2 orders of magnitude, substantially larger than its moderate in-plane friction anisotropy and the values reported for high-symmetry layered materials. Atomic-resolution lateral force mapping reveals a hierarchical friction landscape composed of atomic lattice corrugation and twist-induced moiré modulation, with the moiré wavelength evolving systematically with relative misorientation. These results show that interlayer friction in low-symmetry 2D materials is governed by a multiscale, orientation-dependent potential energy landscape and constitutes an independent mechanical degree of freedom. The conformal probe platform provides a general route to probe and engineer direction-selective interlayer mechanics in van der Waals systems.