滑块厚度提高润滑性：从2D岛到3D簇
Slider Thickness Promotes Lubricity: from 2D Islands to 3D Clusters
摘要：
吸附在晶体表面的三维团簇和二维岛的滑动是理解摩擦的重要测试案例。即使对于相同的材料，单原子岛和厚团簇通常也不会表现出相同的摩擦力，但尚未探索具体的差异。通过现实的分子动力学模拟的静摩擦金在石墨，实验相关的系统，我们发现作为金厚度的函数的逐步下降的静摩擦从单层岛，很容易被钉扎，对集群，更容易滑动。对这种厚度引起的润滑性有贡献的主要成分似乎是原子接触的有效刚性增加，起到减少与基底的簇交错的作用。起作用的第二个元素是横向接触的大小，它可以容纳孤立子典型的无公度界面仅高于临界接触直径，这是更大的单层岛比厚集群。这两种效应一致地使集群比岛屿更润滑，并且大尺寸比小尺寸更润滑。这些结论预计将是更广泛的适用性在不同的纳米摩擦学系统，其中所发挥的作用，静态和动态，摩擦通常是相当重要的。
英文摘要：
The sliding of three-dimensional clusters and two-dimensional islands adsorbed on crystal surfaces represent an important test case to understand friction. Even for the same material, monoatomic islands and thick clusters will not as a rule exhibit the same friction, but specific differences have not been explored. Through realistic molecular dynamics simulations of the static friction gold on graphite, an experimentally relevant system, we uncover as a function of gold thickness a progressive drop of static friction from monolayer islands, that are easily pinned, towards clusters, that slide more readily. The main ingredient contributing to this thickness-induced lubricity appears to be the increased effective rigidity of the atomic contact, acting to reduce the cluster interdigitation with the substrate. A second element which plays a role is lateral contact size, which can accommodate the solitons typical of the incommensurate interface only above a critical contact diameter, which is larger for monolayer islands than for thick clusters. The two effects concur to make clusters more lubric than islands, and large sizes more lubric than smaller ones. These conclusions are expected to be of broader applicability in diverse nanotribological systems, where the role played by static, and dynamic, friction is generally quite important.
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