Towards superlubricity in nanostructured surfaces: the role of van der Waals forces

Hydrogenated amorphous carbon (a-C:H) thin films have a unique combination of properties that are fundamental in mechanical and electromechanical devices aimed at energy efficiency issues. The literature brings a wealth of information about the ultra-low friction (superlubricity) mechanism in a-C:H...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP 2018, Vol.2 (34), p.21949-21959
Main Authors: Echeverrigaray, Fernando G, de Mello, Saron R, Leidens, Leonardo M, Maia da Costa, Marcelo E, Alvarez, Fernando, Burgo, Thiago A. L, Michels, Alexandre F, Figueroa, Carlos A
Format: Article
Language:English
Subjects:
Carbon
Electric contacts
Electromechanical devices
Friction
Hydrogen storage
Hydrogenation
Nanostructure
Sliding
Thin films
Van der Waals forces
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Summary:Hydrogenated amorphous carbon (a-C:H) thin films have a unique combination of properties that are fundamental in mechanical and electromechanical devices aimed at energy efficiency issues. The literature brings a wealth of information about the ultra-low friction (superlubricity) mechanism in a-C:H thin films. However, there is persistent controversy concerning the physicochemical mechanisms of contact mechanics at the atomic/molecular level and the role of electrical interactions at the sliding interface is still a matter of debate. We find that the hydrogenation of the outermost nanostructured surface atomic layers of a-C:H thin films is proportional to the surface potential and also to the friction forces arising at the sliding interface. A higher hydrogen-to-carbon ratio reduces the surface potential, directly affecting frictional forces by a less effective long-term interaction. The structural ultra-low friction (superlubricity) is attributed to a lower polarizability at the outermost nanostructured layer of a-C:H thin films due to a higher hydrogen density, which renders weaker van der Waals forces, in particular London dispersion forces. More hydrogenated nanodomains at the surface of a-C:H thin films are proposed to be used to tailor superlubricity. Energy dissipation associated with frictional damping mechanisms owing to van der Waals (vdW) forces by induced polarizability at the sliding interface of a-C:H thin films.
ISSN:1463-9076
1463-9084
DOI:10.1039/c8cp02508h