No abstract

The bonding sites for Au-adatom-octanethiolate within the (√3×√3)R30° structure on Au(111) have been investigated with high-resolution scanning tunneling microscopy (STM) imaging. By establishing the relationship between the lateral positions of adsorbates on the top layer of gold and those inside an etch pit, we are able to determine the adsorption configuration with a high degree of accuracy for the elusive (√3×√3)R30° molecular layer. The boundary between adjacent SAM domains is also imaged with molecular resolution that allows the assignment of adsorption site in each domain without ambiguity. The standard (√3×√3)R30° alkanethiol SAM on Au(111) is found to consist of domains with Au-adatom-octanethiolate occupying the fcc hollows site, alongside domains where the hcp hollow site is occupied.

Self-assembled monolayers (SAMs) of Au-octanethiolate on Au(111) have been studied using scanning tunneling microscopy (STM). Thermal annealing of the dense (square root(3) x square root(3))R30 degrees layer at 353 K for 1 h leads to the formation of a (5 square root(3) x square root(3))R30 degrees striped phase coexisting with the (square root(3) x square root(3))R30 degrees phase. High-resolution STM imaging shows that the unit cell of the (5 square root(3) x square root(3))R30 degrees phase consists of four adsorbed Au-thiolate species giving rise to an adsorbate coverage of 0.27 ML. The four Au-thiolate species take the standing-up orientation and occupy inequivalent adsorption sites: one on a bridge site and three on the hollow sites. By drawing connections between the (5 square root(3) x square root(3))R30 degrees and the (square root(3) x square root(3))R30 degrees phases, it is found that the adsorption site for Au-thiolate inside the (square root(3)3 x square root(3))R30 degrees phase must be either the fcc hollow or the hcp hollow site.