Thermal study and structural characterization of self-assembled monolayers generated from diadamantane disulfide on Au(1 1 1)

Self-assembled monolayers (SAMs) formed from diadamantane disulfide (DADS) on Au(1 1 1) have been characterized using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and infrared reflection absorption spectroscopy (IRRAS). SAMs of DADS prepared at room temperature (RT) were found to form at least four different orientational ordered domains having densely packed and well-ordered structure with nearest neighbour distance of 7.0 ± 0.3 Å. The spectroscopic techniques used in this work reveal the formation of highly oriented SAMs with molecular axis orientated perpendicular to the surface. Annealing the SAMs prepared at RT to temperatures below 353 K results in no structural changes from that observed at RT. The samples that annealed at temperatures higher than 353 K exhibited different surface morphologies and structural changes were observed for these SAMs. In addition, the number of the different rotational domains is reduced to three after this annealing. After annealing at 353–393 K, the domain boundaries that were missed in SAMs prepared at RT or after annealing at temperature lower than 353 K appear in a shape similar to those observed for n-alkanethiols on Au(1 1 1). Moreover, the SAMs show a highly ordered hexagonal close-packed molecular lattice with a measured nearest neighbour distance of 7.6 ± 0.1 Å, corresponding to a image unit cell.