Orientation and order of self-assembled p-benzenedimethanethiol films on Pt(111) obtained by direct adsorption and via alkanethiol displacement

Self-assembly of p-benzenedimethanethiol (p-BDMT) on Pt(111) has been investigated by high-resolution electron energy loss spectroscopy and sum-frequency generation spectroscopy. The molecules adsorb on Pt(111) like on gold, attached through one single thiol, leaving the second thiol moiety unreacted and exposed to the outer surface. Yet, the order of the p-BDMT self-assembled film is poor in comparison to alkanethiol SAMs. Displacement in solution of a preadsorbed pentanethiol (PTT) SAM by p-BDMT molecules proved to be a successful approach to achieve films of higher quality, where the size of the dithiol molecular domains tends toward the size measured for PTT. Nearly complete exchange is accomplished after 42 h. However, no significant exchange is observed when dodecanethiol replaces PTT. Displacing the alkanethiols by benzenethiol leads to the same conclusions, suggesting that the exchange processes are lessened as compared to gold.