The formation of striped phases of dialkyl disulfides and dialkyl sulfides on Au(111) and graphite has been monitored by scanning tunneling microscopy (STM) to investigate differences in adsorption of the sulfide to the gold surface. Striped phases formed by C18H37S- moieties after S-S bond cleavage of dioctadecyl disulfide on the gold surface were observed. On the other hand, self-assembled monolayers (SAMs) of dioctadecyl disulfide and dioctadecyl sulfide adsorbed on a graphite surface displayed long-range, well-ordered monolayers with one striped pattern that shows uniform periodicity as a function of molecular length via nondissociative adsorption. In the case of dioctadecyl sulfide SAMs on gold, molecular ordering was identical in periodicity and pattern to the striped phase of SAMs formed by physisorption on the graphite surface. In addition, the striped phase of dioctadecyl sulfide SAMs formed upon a 22 times; √3 surface reconstruction of Au(111) was clearly observed for the first time in the SAM system as physisorbed monolayers. From our STM results, we suggest that the formation of dialkyl sulfide SAMs on gold proceeds via a nondissociative adsorption process unlike the case of dialkyl disulfide SAMs, as revealed mainly by macroscopic techniques. In this study, we have successfully revealed and compared the adsorption processes of dialkyl disulfides and dialkyl sulfides for the first time from a nanoscopic viewpoint.
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