Tribological properties of self-assembled monolayers of fluorocarbon and hydrocarbon thiols and disulfides on Au(111) studied by scanning force microscopy

The tribological properties of highly ordered self-assembled monolayers (SA Ms) of fluorocarbon and hydrocarbon thiols and disulfides formed on triangu lar Au(111) terraces were studied by scanning force microscopy (SFM). Molec ular resolution SFM images proved the high degree of lateral order in the f ilms. The magnitude of friction between Si3N4 tips and the monolayers measu red by SFM was related to the order of the alkane chains. The disorder of t he hydrocarbon chains in SAMs of mixed hydrocarbon - fluorocarbon disulfide s, or short chain hydrocarbon disulfides, was determined by Fourier transfr om infrared (FTIR) spectroscopy. Conformational and structural disorder was found to correlate with a significant increase in the magnitude of frictio n. The correlation between disorder (transition from 'solid-like' to 'amorp hous-like' monolayers) and increase in observed friction force can be inter preted based on models by Yoshizawa et al. [H, Yoshizawa, Y.-L. Chen, J. Is raelachvili, J. Phys. Chem. 97 (1993) 4128]. (C) 1999 Elsevier Science S.A. All rights reserved.