Journal
ACS NANO
Volume 11, Issue 8, Pages 7642-7647Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.7b02240
Keywords
nanotribology; structural superlubricity; AFM manipulation of nanoparticles; incommensurate interfaces; shear stress
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Funding
- German Research Foundation [DI917/5-1]
- COST Action [MP1303]
- Laboratory for Material Science of the Justus Liebig University Giessen [APVV-0759-15, VEGA 2/0162/15, 2/0167/16]
- V4-Japan Joint Research Program on Advanced Materials (NaMSeN) projects
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Structural superlubricity describes the state of-virtually frictionless sliding if two atomically flat interfaces are incommensurate, that is, they share no common periodicity. Despite the exciting prospects of this low friction phenomenon, there are physical limitations to the existence of this state. Theory predicts that the contact size is one fundamental limit, where the critical size threshold mainly depends on the interplay between lateral contact compliance and interface interaction energies. Here we provide experimental evidence for this size threshold by measuring the sliding friction force of differently sized antimony particles on MoS2. We find that superlubric sliding with the characteristic linear decrease of shear stress with contact size prevails for small particles with contact areas below 15 000 nm(2). Larger particles, however, show a transition toward constant shear stress behavior. In contrast, Sb particles on graphite show superlubricity over the whole size range. Ab initio simulations reveal that the chemical interaction energies for Sb/ MoS2 are much stronger than for Sb/HOPG and can therefore explain the different friction properties as well as the critical size thresholds. These limitations must be considered when designing low friction contacts based on structural superlubricity concepts.
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