Adsorption and self-organization of sodium alkyl sulfonates (STS and SHS) have been studied on HOPG by using the in situ scanning tunneling microscopy (STM). Both SHS and STS molecules adsorb on the HOPG surface and form long-range well-ordered monolayers. The neighboring molecules in different rows form a 'head to head' configuration. In the high-resolution images of STS and SHS molecules, one end of the molecules shows bright spots which are attributed to the SO3- groups.
