Surface structure of a fluorinated thiol on Au(111) by scanning force microscopy

Scanning force microscopy (SFM) was used to study the surface structure of CF3CF2(CH2)(6)SH (7,7,8,8,8-pentafluorooctanethiol, PFOT) monolayers self-assembled from a 1 mM trichloroethene (TCE) solution on Au(111). We observed many depressions with several to 20 nm diameters and 0.24 nm depth. in addition, especially around the step edges of Au, mounds 0.3-0.8 nm in height and with lower friction and higher stiffness than those of other regions were observed. These properties would result from the difference in the molecular orientation between on the mounds and on the flat parts. The molecular arrangement with the (root 3X root 3) R30 degrees structure was observed on the terraces of Au(111). By comparing the film thickness and the molecular length, the tilt angle of the molecular chain was found to be 56-76 degrees with respect to the surface normal. This large tilt angle allows the PFOT SAMs with the relatively large CF3CF2- end group to pack closely on the (root 3X root 3) R30 degrees structure.