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 ultrahigh vacuum has been studied using scanning tunneling microscopy (STM). Two structural phases are observed, a "honeycomb" phase and a pseudo-(100) reconstructed surface phase, which are essentially equivalent to methanethiolate structures observed on Cu(111) in a recent study using STM. The pseudo-(100) structure can also be reconciled with the results of a prior study of this 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 similarity of the behavior of octanethiol and methanethiol on Cu(111), contrast this with alkanethiol behavior on Au(111), and discuss the role of S-substrate interactions in the structures of these self-organized monolayers.