# Synopsis: Slip Sliding Away

#### Observation of High-Speed Microscale Superlubricity in Graphite

Jiarui Yang, Ze Liu, Francois Grey, Zhiping Xu, Xide Li, Yilun Liu, Michael Urbakh, Yao Cheng, and Quanshui Zheng

Published June 20, 2013

Friction can represent a key obstacle to the miniaturization of devices like the read/write heads in a hard drive. Because they have a high surface-to-volume ratio, nanoscale components are particularly susceptible to friction–and thus wear—as they move in contact with a solid surface. This problem has motivated research on a recently discovered phenomenon called superlubricity: a regime of nearly vanishing friction that kicks in when the two sliding surfaces are “incommensurate,” i.e., when the atoms on one surface have a different spacing than those on the counterface.

Researchers have been able to study superlubricity by using a fine tip to slide small objects against a surface, but technical hurdles limit such observations to small sliding speeds (less than $\sim 10$ micron/s), far from those of practical relevance. Now, in an article in Physical Review Letters, Jiarui Yang at the Tsinghua University, China, and colleagues report that two micron-sized, incommensurate layers of graphite can slide against each other at a speed that is over six orders of magnitude higher than that seen in previous superlubricity experiments.

The authors used a tungsten tip to move the upper layer of a graphite mesa, misorienting it (thus making it incommensurate) and sliding it laterally. From previous work, they knew the layer tends to retract to its original position, driven like a spring by interlayer van der Waals forces. In the new study, a laser beam was used to monitor the layer’s position as a function of time. The results revealed that sliding of the layers occurred in a low-friction regime of superlubrication, with retracting speeds of up to $25\phantom{\rule{0.333em}{0ex}}\text{m}/\text{s}$. – Matteo Rini