Structure of the pentylthiolate self-assembled monolayer on Ag(111)

A combination of scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and normal incidence X-ray standing waves (NIXSW) has been used to investigate the structure of the self-assembled monolayer (SAM) formed by pentylthiolate on Ag(111) in ultrahigh vacuum through interaction with pentanethiol. NIXSW data are closely similar to those for memythiolate on Ag(111) in the commensurate (√7×√7)R19° phase and consistent with a similar adsorbate-induced reconstruction of the outermost Ag layer comprising only 3/7 ML of Ag atoms. However, both STM and LEED show that the local lateral periodicity is ∼5% larger in the pentylthiolate phase and that the resulting SAM is not commensurate with the substrate. The results are discussed in the context of previously published results for other alkylthiolate SAMs on Ag(111).