SURFACE-STRUCTURE OF A FLUORINATED THIOL ON AU(111) BY SCANNING FORCEMICROSCOPY

Scanning force microscopy (SFM) was used to study the surface structur e of CF3CF2(CH2)(6)SH (7,7,8,8,8-pentafluorooctanethiol, PFOT) monolay ers self-assembled from a 1 mM trichloroethene (TCE) solution on Au(11 1). We observed many depressions with several to 20 nm diameters and 0 .24 nm depth. in addition, especially around the step edges of Au, mou nds 0.3-0.8 nm in height and with lower friction and higher stiffness than those of other regions were observed. These properties would resu lt from the difference in the molecular orientation between on the mou nds 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 a ngle 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 wit h the relatively large CF3CF2- end group to pack closely on the (root 3X root 3) R30 degrees structure.