Tip-Induced Structural Rearrangements of Alkanethiolate Self-Assembled Monolayers on Gold

A method for preparing self-assembled monolayers of decanethiolate on Au(111) with large (ca. 50−100 nm) regions of hexagonal (√3×√3 R30) lattice is reported. Such samples could be transformed from this structure to a c(4×2) superlattice under the influence of a scanning tunneling microscope (STM) tip. These images were comparable to those obtained by thermally annealing the sample. Using an atomic force microscope tip in friction force mode (FFM), the c(4×2) superlattice could be observed on thermally annealed samples, but pressing upon the sample with a moderate tip load (as high as 80 nN) did not induce this structure. Comparative analysis of the results obtained by these two techniques suggests that this transformation occurred as the result of the tip pressing upon the surface. In addition to this final structure, intermediate structures were observed during these tip-induced transformations. The STM-induced transformation revealed an intermediate structure of p2 symmetry. The FFM-induced transformat...