Measuring nanoscale friction at graphene step edges
Measuring nanoscale friction at graphene step edges
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DOI：
10.1007/s40544-019-0334-y
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发表时间：
2019-12
期刊：
影响因子：
6.8
通讯作者：
Zhe Chen;Seong H. Kim
中科院分区：
文献类型：
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作者：
Zhe Chen;Seong H. Kim
尽管石墨烯在其基面上的超润滑性是众所周知的，但其台阶边缘处的摩擦并没有得到很好的理解，并且已经报道了矛盾的摩擦行为。在这项研究中，单层厚石墨烯台阶边缘的摩擦进行了研究，使用原子力显微镜（AFM）与硅针尖在干燥的氮气气氛中。据发现，当尖端滑过“掩埋”石墨烯台阶边缘时，由于地形高度变化，在步进运动期间存在阻力，在步进运动期间存在辅助力。这两个力的大小很小，并且在步进和步进运动中是相同的。至于“暴露的”石墨烯台阶边缘，摩擦增加的幅度，并表现出更复杂的行为。在步下运动的尖端在暴露的步骤边缘，电阻和辅助组件可以检测到的横向力信号的AFM，如果扫描分辨率是足够高的。电阻成分是由于在尖端和台阶边缘表面的官能团之间的化学相互作用，和辅助成分是由于地形效应，埋台阶边缘的情况下相同。如果使用钝头，这两个组件的不同效果变得更加突出。在步进扫描方向上，钝尖似乎有两个独立的地形效应，弹性变形的接触区域在底部的尖端，由于基板的高度变化在台阶边缘和倾斜的尖端，而悬臂的垂直位置（尖端的末端）上升，从较低的平台到较高的平台。石墨烯台阶边缘处摩擦行为的高分辨率测量将进一步丰富对石墨烯覆盖表面上界面摩擦行为的理解。
Although graphene is well known for super-lubricity on its basal plane, friction at its step edge is not well understood and contradictory friction behaviors have been reported. In this study, friction of mono-layer thick graphene step edges was studied using atomic force microscopy (AFM) with a Si tip in dry nitrogen atmosphere. It is found that, when the tip slides over a ‘buried’ graphene step edge, there is a resistive force during the step-up motion and an assistive force during the step-down motion due to the topographic height change. The magnitude of these two forces is small and the same in both step-up and step-down motions. As for the ‘exposed’ graphene step edge, friction increases in magnitude and exhibits more complicated behaviors. During the step-down motion of the tip over the exposed step edge, both resistive and assistive components can be detected in the lateral force signal of AFM if the scan resolution is sufficiently high. The resistive component is attributed to chemical interactions between the functional groups at the tip and step-edge surfaces, and the assistive component is due to the topographic effect, same as the case of buried step edge. If a blunt tip is used, the distinct effects of these two components become more prominent. In the step-up scan direction, the blunt tip appears to have two separate topographic effects elastic deformation of the contact region at the bottom of the tip due to the substrate height change at the step edge and tilting of the tip while the vertical position of the cantilever (the end of the tip) ascends from the lower terrace to the upper terrace. The high-resolution measurement of friction behaviors at graphene step edges will further enrich understanding of interfacial friction behaviors on graphene-covered surfaces.