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Scratching of Graphene-Coated Cu Substrates Leads to Hardened Cu Interfaces with Enhanced Lubricity
journal contribution
posted on 2020-02-13, 22:44 authored by Shuji Zhao, Songlin Shi, Kailun Xia, Tao Wang, Maosheng Chai, Yingying Zhang, Cangyu Qu, Quanshui ZhengThe decrease in friction
is often observed in the initial period
of sliding a fresh contact between two solid surfaces. This phenomenon
is usually termed running-in. Here we report a running-in phenomenon
observed in single-layer graphene grown on a Cu substrate. By repeatedly
scratching the graphene surface using the tip of an atomic force microscope
(AFM), it is found that the frictional force decreases within the
first tens of scratching cycles and then approaches to a steady state,
whereas the graphene coating stays free of wear and damage. Through
specially designed experiments on changing normal load and sliding
velocity as well as indentation tests by AFM, the mechanism behind
this running-in process is revealed to be the hardening of the underlying
Cu substrate. These observations and understandings can help future
development of macroscale graphene-coated substrates with superlubricity.