The influence of packing densities and surface order on the frictional properties of alkanethiol self-assembled monolayers (SAMs) on gold: A comparison of SAMS derived from normal and spiroalkanedithiols

We report a comparative study of the structure and frictional properties of self-assembled monolayers (SAMs) generated by the adsorption of three homo logous 17-carbon alkanethiols-heptadecanethiol, 2,2-dipentadecyl-1,3-propan edithiol, and 2-pentadecyl-1,3-propanedithiol-onto the surface of Au(lll). The structural properties of these SAMs were characterized by atomic force microscopy, surface infrared spectroscopy, X-ray photoelectron spectroscopy , spectral ellipsometry, and wettability by water and hexadecane. The frict ional properties of the SAMs were examined by friction force microscopy. Th e results demonstrate that the packing density and the related crystalline order of the hydrocarbon chains influence the frictional properties of orga nic thin films. The origins of the frictional differences measured from the se films are discussed in terms of the structure of the films.