Vazirisereshk Mohammad R, Hasz Kathryn, Carpick Robert W, Martini Ashlie
Department of Mechanical Engineering, University of California, Merced, California 95343, United States.
Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
J Phys Chem Lett. 2020 Aug 20;11(16):6900-6906. doi: 10.1021/acs.jpclett.0c01617. Epub 2020 Aug 11.
Atomic-scale friction measured for a single asperity sliding on 2D materials depend on the direction of scanning relative to the material's crystal lattice. Here, nanoscale friction anisotropy of wrinkle-free bulk and monolayer MoS is characterized using atomic force microscopy and molecular dynamics simulations. Both techniques show 180° periodicity (2-fold symmetry) of atomic-lattice stick-slip friction vs. the tip's scanning direction with respect to the MoS surface. The 60° periodicity (6-fold symmetry) expected from the MoS surface's symmetry is only recovered in simulations where the sample is rotated, as opposed to the scanning direction changed. All observations are explained by the potential energy landscape of the tip-sample contact, in contrast with nanoscale topographic wrinkles that have been proposed previously as the source of anisotropy. These results demonstrate the importance of the tip-sample contact quality in determining the potential energy landscape and, in turn, friction at the nanoscale.
在二维材料上滑动的单个微凸体的原子尺度摩擦力取决于相对于材料晶格的扫描方向。在此，使用原子力显微镜和分子动力学模拟对无褶皱的块状和单层二硫化钼的纳米尺度摩擦各向异性进行了表征。两种技术均显示出原子晶格粘滑摩擦相对于尖端相对于二硫化钼表面的扫描方向具有180°周期性（二重对称性）。二硫化钼表面对称性预期的60°周期性（六重对称性）仅在样品旋转而非扫描方向改变的模拟中得以恢复。与先前提出的作为各向异性来源的纳米尺度地形褶皱相反，所有观察结果均由尖端-样品接触的势能面来解释。这些结果证明了尖端-样品接触质量在确定势能面进而确定纳米尺度摩擦力方面的重要性。
