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

Markos Paradinas*, Carmen Munuera, Christophe Silien, Manfred Buck, Carmen Ocal

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)

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 omega-(4'-methylbiphenyl-4-yl) butane-1-thiol coexisting on Au(111) are investigated by scanning tunneling and force microscopy. Described by rectangular 5 root 5 x 3 (alpha-phase) and oblique 6 root 3 x 2 root 3 (beta-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 beta-phase for which the separate analysis of forward and backward lateral force scans is used to differentiate domains rotated 180 degrees. The results demonstrate the level of structural control required in the design of SAMs for nano-tribology applications.

Original languageEnglish
Pages (from-to)1302-1309
Number of pages8
JournalPhysical Chemistry Chemical Physics
Volume15
Issue number4
DOIs
Publication statusPublished - 2013

Keywords

  • ASYMMETRY
  • SURFACE
  • AU(111)
  • ALKANETHIOLS
  • GOLD
  • MOLECULAR PACKING
  • BIPHENYL-BASED THIOLS
  • SCANNING-TUNNELING-MICROSCOPY
  • ANISOTROPY
  • ATOMIC-FORCE MICROSCOPE

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