Self-assembly and functional group effect of asymmetric disulfides on graphite studied by scanning tunneling microscopy

Well-ordered self-assembled monolayers of asymmetric disulfides on graphite were observed by scanning tunneling microscopy (STM). STM images showed th at the molecules are oriented parallel to the graphite surface without diss ociation of the sulfur-sulfur bond. The adsorption phase of 11-hydroxyundec yl octadecyl disulfide (CH3(CH2)(17)SS (CH2)(11)OH) molecules on graphite i s governed by the formation of a hydrogen bond with a hydroxyl group facing another hydroxyl group of adjacent molecules. Self-assembled monolayers of octadecyl undecyl disulfide (CH3(CH2)(17)SS(CH2)(10)CH3) molecules, on the other hand, showed different ordering periodicity compared to that of hydr oxylated disulfide molecules.