Chemisorption-induced gap state at organic–metal interface: Benzenethiol on Pt(111)

Abstract

Electron emission spectra obtained by thermal collisions of He*(2³S) metastable atoms with benzenethiol (C₆H₅SH) on Pt(111) were measured to characterize the chemisorption-induced gap state (CIGS) formed at the organic–metal interface. First-principles calculations using density functional theory were also performed for an ordered thiolate (C₆H₅S) monolayer on Pt(111). Our data exhibit that the CIGS due to the S 3p–Pt 5d mixings appears just below the Fermi level (E_F) of the substrate, where the local density of states decreases drastically from the S terminal to the benzene ring. Furthermore, strong benzene π(1e_1g)–S 3p couplings are apparently lifted upon the formation of thiolate. These features indicate that thiolate is not a good mediator of metal wave functions at E_F, which is closely related to tunneling probability (and eventually electric conductance) in the relevant metal–organic–metal junctions at zero bias.