A combined spectroscopic and theoretical study has been performed to clarify the local electronic properties induced at the C 60 -Pt(111) interface. The C 60 molecules are regularly bound to the Pt(111) substrate via covalent bond, forming hybridized states just below the Fermi level (E F ). Such a metallic feature is originated by strong Pt 5d-C 60 π couplings and is extended to the entire molecule, indicating that the adsorbed C 60 molecule serves as an excellent mediator of metal wave function. Our findings correspond well to an extremely high conductivity in C 60 bridged by a pair of Pt electrodes and will provide a useful guide for fabricating moleculebased devices.

Electron emission spectra resulting from thermal collision of He ‫ء‬ ͑2 3 S͒ atoms with 2,9-demethyl-4,7-diphenyl-1,10-phenanthroline ͑BCP͒ films deposited on metal substrates were measured to characterize gap states emerged at the organic-metal interface. For BCP on Au, the gap state is originated from weak chemisorption and serves as a mediator of metal wave functions to the first layer. For BCP on K, organic-metal complex is formed by spontaneous diffusion, yielding the gap states delocalized over the film. In the interfacial region, all the gap state reveals an incommensurate shift with the valence band top of the film, indicating the breakdown of the Schottky-Mott model as evaluating the transport characteristics in organic-metal system.

The valence electronic states of thiophene (TP), 2-thiophenethiol (TT), 2,2'-bithiophene (BTP), and 2,2'-bithiophene-5-thiol (BTT) on Pt(111) were measured by ultraviolet photoemission spectroscopy (UPS) and metastable atom electron spectroscopy (MAES) to elucidate how the local electronic properties at the organic-metal interface are altered by the extent of π-conjugation and substituent effects. First-principles calculations using density functional theory (DFT) were used to assign the observed spectra. TP and BTP chemisorb weakly on Pt(111), whereas TT and BTT are strongly bound to Pt(111) through the S atom with the cleavage of the S-H bond, forming a thiolate. In the MAES spectra, weak emission just below the Fermi level (E(F)) was attributed to a chemisorption-induced gap state (CIGS) produced by orbital mixing between the organic species and Pt(111). The formation of CIGS is responsible for a metallic structure at the organic-metal interface. The relative intensities of CIGSs at E(F) were in the order of TP (flat-lying configuration) > TT > TP (inclined configuration), indicating that the spatial distribution of CIGSs is drastically altered by the strength of the organic-metal bond and the adsorption geometry. In other words, TP (flat-lying geometry) and TT serve as good mediators of the extension of the metal wave function at E(F), which would be closely related to charge transport at organic-metal interfaces.

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