Origin of High Friction at Graphene Step Edges on Graphite
Origin of High Friction at Graphene Step Edges on Graphite
复制标题
石墨烯阶梯边缘高摩擦力的起源
DOI：
10.1021/acsami.0c18098
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发表时间：
2021
影响因子：
9.5
通讯作者：
Kim, Seong H.
中科院分区：
文献类型：
--
作者：
Chen, Zhe;Khajeh, Arash;Martini, Ashlie;Kim, Seong H.
在石墨上，已知与在基面上相比，在台阶边缘缺陷处的摩擦大于一个数量级，特别是当相对表面从台阶的下台阶滑动到上台阶时。已经提出了非常不同的机制来解释这种现象，包括相对表面和台阶边缘之间的原子相互作用（没有物理变形）以及上石墨烯平台的屈曲或剥离变形。在这里，我们使用原子力显微镜（AFM）和反应分子动力学（MD）模拟捕捉和区分机制，提出在步骤边缘造成高摩擦。AFM实验揭示了无变形和屈曲变形的情况之间的差异，后者的情况是由于滑动尖端施加的物理应力。反应MD模拟探索剥离变形的过程中，由于尖端和台阶边缘之间的摩擦化学键的形成。结合AFM实验和MD模拟的结果，发现每个机制具有可识别的和特征的横向力和垂直的高度轮廓记录在升压过程中。结果表明，在典型的AFM实验条件下，石墨烯边缘的屈曲和剥离变形很少发生，因此在大多数测量中不太可能是台阶边缘处高摩擦的起源。相反，高的步进摩擦是由于在没有石墨烯本身变形的情况下由尖端和台阶边缘之间的形貌变化和原子相互作用促进的粘滑行为。
On graphite, friction is known to be more than an order of magnitude larger at step edge defects as compared to on the basal plane, especially when the counter surface slides from the lower terrace of the step to the upper terrace. Very different mechanisms have been proposed to explain this phenomenon, including atomic interactions between the counter surface and step edge (without physical deformation) and buckling or peeling deformation of the upper graphene terrace. Here, we use atomic force microscopy (AFM) and reactive molecular dynamic (MD) simulations to capture and differentiate the mechanisms proposed to cause high friction at step edges. AFM experiments reveal the difference between cases of no deformation and buckling deformation, and the latter case is attributed to the physical stress exerted by the sliding tip. Reactive MD simulations explore the process of peeling deformation due to tribochemical bond formation between the tip and the step edge. Combining the results of AFM experiments and MD simulations, it is found that each mechanism has identifiable and characteristic features in the lateral force and vertical height profiles recorded during the step-up process. The results demonstrate that buckling and peeling deformation of the graphene edge rarely occur under typical AFM experimental conditions and thus are unlikely to be the origin of high friction at step edges in most measurements. Instead, the high step-up friction is due to stick–slip behavior facilitated by the topographical change and atomic interactions between the tip and step edge without deformation of the graphene itself.