Theory predicts that two-dimensional (2D) materials may only exist in the presence of out-of-plane deformations on atomic length scales, frequently referred to as ripples. While such ripples can be detected via electron microscopy, their direct observation via surface-based techniques and characterization in terms of interaction forces and energies remain limited, preventing an unambiguous study of their effect on mechanical characteristics, including but not limited to friction anisotropy. Here, we employ high-resolution atomic force microscopy to demonstrate the presence of atomic-scale ripples on supported samples of few-layer molybdenum disulfide (MoS₂). Three-dimensional force/energy spectroscopy is utilized to study the effect of ripples on the interaction landscape. Friction force microscopy reveals multiple symmetries for friction anisotropy, explained by studying rippled sample areas as a function of scan size. Our experiments contribute to the continuing development of a rigorous understanding of the nanoscale mechanics of 2D materials.

理论预测，二维（2D）材料可能仅存在于原子长度尺度上的平面外变形（通常称为波纹）的情况下。尽管可以通过电子显微镜检测到这种波纹，但通过基于表面的技术对其进行直接观察以及在相互作用力和能量方面进行表征仍然受到限制，从而阻止了对它们对机械特性（包括但不限于摩擦各向异性）的影响的明确研究。在这里，我们使用高分辨率原子力显微镜来证明在几层二硫化钼（MoS ₂）。利用三维力/能谱研究了波纹对相互作用景观的影响。摩擦力显微镜揭示了摩擦各向异性的多种对称性，这是通过研究波纹状样品面积与扫描尺寸的函数来解释的。我们的实验有助于对二维材料纳米尺度力学的严格理解的不断发展。