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Issue 4, 2013
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Heterogeneous nanotribological response of polymorphic self-assembled monolayers arising from domain and phase dependent friction

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Abstract

Micro-/nanoelectromechanical systems demand robust ultrathin films for lubrication. As they can drastically modify the frictional properties of surfaces, few nanometers thick self-assembled monolayers (SAMs) constitute accepted candidates as boundary lubricants. Their high stability and easy preparation make them attractive also for low cost applications. Given their high order, organosulfur SAMs have been archetypal systems for structural investigations, but few efforts have been devoted to analyze the influence of lateral inhomogeneities on their surface properties. The impact on the frictional response of the surface due to the existence of crystalline domains with lateral dimension in the sub-micrometer range is considered here. To this end, two polymorphic structures of self-assembled monolayers of ω-(4′-methylbiphenyl-4-yl) butane-1-thiol coexisting on Au(111) are investigated by scanning tunneling and force microscopy. Described by rectangular Image ID:c2cp43769d-t1.gif (α-phase) and oblique Image ID:c2cp43769d-t2.gif (β-phase) unit cells, they exhibit pronouncedly different frictional responses. The lateral nano-tribological heterogeneity of the surface is further influenced by the azimuthal orientation dependence of friction for each phase. In particular, this phenomenon is exploited in the less densely packed β-phase for which the separate analysis of forward and backward lateral force scans is used to differentiate domains rotated 180°. The results demonstrate the level of structural control required in the design of SAMs for nano-tribology applications.

Graphical abstract: Heterogeneous nanotribological response of polymorphic self-assembled monolayers arising from domain and phase dependent friction

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Article information


Submitted
25 Oct 2012
Accepted
21 Nov 2012
First published
22 Nov 2012

Phys. Chem. Chem. Phys., 2013,15, 1302-1309
Article type
Paper

Heterogeneous nanotribological response of polymorphic self-assembled monolayers arising from domain and phase dependent friction

M. Paradinas, C. Munuera, C. Silien, M. Buck and C. Ocal, Phys. Chem. Chem. Phys., 2013, 15, 1302
DOI: 10.1039/C2CP43769D

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