Imaging of Terphenyldithiol Molecules in Highly Orientated and Ordered Aromatic Dithiol SAMs on Au(111)

In this study, the formation and adlayer structure of highly orientated self-assembled monolayers (SAMs) generated from terphenyldithiol molecules on Au(111) have been characterized by reflection adsorption infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning tunneling microscopy. Our results showed that it is possible to prepare ordered and highly orientated films of dithiol molecules by using ethanol and toluene as solvents and then handling the formed film by a subsequent immersion in a solution of one of the oxidizing agents, TBP or tris(2-carboxyethyl)phosphine (TCEP), for a prolonged period of 18 h. By employing this approach, the reduction of the S-S disulfide bonds that link the terphenyl units between the adjacent adsorbed molecules results in the formation of films that are similar in quality to those obtained from the adsorption of aromatic monothiols on the surface of gold. The saturated monolayer is characterized by a close-packed arrangement of upright standing molecules forming a (2 root 3 x root 3) R30 degrees oblique unit cell. This result is of particular interest as, to the best of our knowledge, this study is the first example of acquiring molecularly resolved scanning tunneling microscope (STM) images of aromatic dithiol SAMs in which individual terphenyldithiol molecules were topographically imaged.