Structural characterization and frictional properties of C60-terminated self-assembled monolayers on Au(111)

C-60-terminated self-assembled monolayers (SAMs) were generated on the surface of Au(111) by the adsorption of unsymmetrical disulfides having saturated hydrocarbon backbone structures comprised of six (C-6) and eleven (C-11) carbon atoms. The formation of oriented monolayer films from these adsorbates was confirmed by ellipsometric thickness and contact angle measurements. The morphologies and frictional properties of the C-60-terminated SAMs were examined using atomic force microscopy (AFM). The SAMs derived from the C-11 disulfides exhibited smooth morphologies and homogeneous frictional force distributions, which proved ideal for the study of intrinsic frictional properties. The SAMs derived from the C-6 disulfides, however, exhibited rough and inhomogeneous topographic and frictional force distributions. In addition, the shorter SAMs exhibited erratic frictional behavior and partial film delamination. The relative frictional forces observed on these immobilized C-60 films were higher than those observed on normal methyl-terminated SAMs and on the surface of graphite. (C) 2000 Elsevier Science S.A. All rights reserved.