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

Author(s)

Echeverrigaray, Fernando G. ^[1] ; de Mello, Saron R. S. ^[1] ; Leidens, Leonardo M. ^[1] ; Maia da Costa, Marcelo E. H. ^[2] ; Alvarez, Fernando ^[3] ; Burgo, Thiago A. L. ^{[4, 5]} ; Michels, Alexandre F. ^{[6, 1]} ; Figueroa, Carlos A. ^{[7, 1]}

Affiliation

^[1] UCS, PGMAT, BR-95070560 Caxias Do Sul, RS - Brazil

^[2] Pontificia Univ Catolica Rio de Janeiro PUC Rio, Dept Fis, BR-22451900 Rio De Janeiro, RJ - Brazil

^[3] Univ Estadual Campinas, UNICAMP, Inst Fis Gleb Wataghin, BR-13083970 Campinas, SP - Brazil

^[4] Univ Estadual Campinas, UNICAMP, Inst Quim, BR-13083970 Campinas, SP - Brazil

^[5] Univ Fed Santa Maria, Dept Fis, BR-97105900 Santa Maria, RS - Brazil

^[6] Univ Fed Rio Grande do Sul UFRGS, Inst Fis, Porto Alegre, RS - Brazil

^[7] Plasmar Tecnol Ltda, BR-95030775 Caxias Do Sul, RS - Brazil

• Document type: Journal article
• Source: Physical Chemistry Chemical Physics; v. 20, n. 34, p. 21949-21959, SEP 14 2018.
• Web of Science Citations: 2

Abstract

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. (AU)

• FAPESP's process: 12/10127-5 - Research and development of nanostructured materials for electronic and surface physics applications
• Grantee: Fernando Alvarez
• Support Opportunities: Research Projects - Thematic Grants