ABSTRACT
Valence electronic states of benzenethiol (C(6)H(5)SH) and benzeneselenol (C(6)H(5)SeH) in the gas, condensed, and chemisorbed phases were examined by ultraviolet photoemission spectroscopy, metastable atom electron spectroscopy, and first-principles calculations using density functional theory. C(6)H(5)SH is chemisorbed on Pt(111) and Au(111) substrates to form a thiolate (C(6)H(5)S), and C(6)H(5)SeH is bound on Pt(111) substrate to form a selenolate (C(6)H(5)Se). In all cases, chemisorption-induced gap states (CIGSs) appear just below the Fermi level (E(F)) of the substrate, yielding a metallic character around the anchor S and Se atoms. However, the local density at E(F) decreases considerably from the anchor atom to the benzene ring, because strong coupling between benzene π(1e(1g)) and S 3p(or Se 4p) in free molecules is apparently lifted upon chemisorption. In other words, thiolates and selenolates (especially C(6)H(5)S on Au(111)) act as poor mediators of the metal wave functions at E(F), which is closely related to electric conductance in the relevant metal-organic-metal junctions at zero bias.
Subject(s)
Benzene Derivatives/chemistry , Gold/chemistry , Organometallic Compounds/chemistry , Organoselenium Compounds/chemistry , Phenols/chemistry , Platinum/chemistry , Sulfhydryl Compounds/chemistry , Adsorption , Quantum Theory , Surface PropertiesABSTRACT
Electron emission spectra obtained by thermal collisions of He*(2(3)S) metastable atoms with benzenethiol (C(6)H(5)SH) 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 (C(6)H(5)S) 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 pi(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.
