Nat Mater. 2010 Aug;9(8):634-7. doi: 10.1038/nmat2798. Epub 2010 Jul 18.
Sliding parts in nanosystems such as nanoelectromechanical systems and nanomotors increasingly involve large speeds, and rotations as well as translations of the moving surfaces; yet, the physics of high-speed nanoscale friction is so far unexplored. Here, by simulating the motion of drifting and of kicked Au clusters on graphite--a workhorse system of experimental relevance--we demonstrate and characterize a new 'ballistic' friction regime at high speed, separate from drift at low speed. The temperature dependence of the cluster slip distance and time, measuring friction, is opposite in these two regimes, consistent with theory. Crucial to both regimes is the interplay of rotations and translations, shown to be correlated in slow drift but anticorrelated in fast sliding. Despite these differences, we find the velocity dependence of ballistic friction to be, like drift, viscous.
在纳米系统（如纳米机电系统和纳米马达）中，滑动部件越来越多地涉及大速度、旋转以及移动表面的平移；然而，高速纳米尺度摩擦的物理学迄今为止尚未得到探索。在这里，通过模拟在石墨上漂移和踢动的 Au 团簇的运动——这是一个具有实验相关性的主力系统——我们展示并描述了在高速下与低速漂移分开的新的“弹道”摩擦状态。在这两个状态下，测量摩擦的团簇滑动距离和时间的温度依赖性是相反的，这与理论一致。对于这两个状态都至关重要的是旋转和平移的相互作用，在缓慢漂移中表现为相关，而在快速滑动中则表现为反相关。尽管存在这些差异，我们发现弹道摩擦的速度依赖性与漂移一样，是粘性的。
