Structural Investigations of the (5x√3) Striped Phase of Annealed 11-Phenoxy Undecanethiol Self-Assembled Monolayers on Au(111)

摘要

Self-assembled monolayers (SAMs) of 11-phenoxyundecanethiol on Au(111) were studied using scanning tunneling microscopy (STM), reflection absorption infrared spectroscopy (RAIRS), ellipsometry, and contact angle measurements before and after annealing in vacuum. The unannealed phenoxy SAM appeared to be disordered under the STM while RAIRS showed that the SAM has relatively significant organization, indicating there is local disordering of the phenoxy groups at the film surface. After annealing, the SAM formed striped domains with a (5x√3) rectangular structure with respect to the gold substrate. Molecularly resolved STM images of the stripes were obtained, and we were able to see that each stripe consists of two rows of molecules. On the basis of the results from all of the characterization techniques used here, we present a structure for the stripes that involve gauche conformations and the phenyl rings interacting in a favorable edge-to-face configuration. This study shows that mild annealing of aromatic SAMs can lead to drastic structural changes, and that aromatic interactions and electrostatic effects play an important role in determining the final structure.