Adsorption structures of 1-octanethiol on Cu(111) studied by scanning tunneling microscopy

The interaction of 1-octanethiol with Cu(111) at room temperature in ultrah igh vacuum has been studied using scanning tunneling microscopy (STM). Two structural phases are observed, a "honeycomb" phase and a pseudo-(100) reco nstructed surface phase, which are essentially equivalent to methanethiolat e structures observed on Cu(111) in a recent study using STM. The pseudo-(1 00) structure can also be reconciled with the results of a prior study of t his phase using normal-incidence X-ray standing wavefield absorption, which indicated the presence of adsorbate-induced reconstruction but was unable to establish further details of the local structure. We discuss the similar ity of the behavior of octanethiol and methanethiol on Cu(111), contrast th is with alkanethiol behavior on Au(111), and discuss the role of S-substrat e interactions in the structures of these self-organized monolayers.