Local electronic properties at organic―metal interfaces: thiophene derivatives on Pt(111)

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...

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Published in:Physical chemistry chemical physics : PCCP 2012-11, Vol.14 (44), p.15412-15420
Main Authors: SATO, Hirofumi, USHIYAMA, Shota, SOGO, Mauo, AOKI, Masaru, SHUDO, Ken-Ichi, SUGAWARA, Tadashi, YANAGISAWA, Susumu, MORIKAWA, Yoshitada, MASUDA, Shigeru
Format: Article
Language:English
Subjects:
Bonding strength
Chemistry
CIGS
Derivatives
ELECTRICAL PROPERTIES
Electronic properties
Electrons
Exact sciences and technology
Fermi level
General and physical chemistry
INTERFACES
Orbitals
ORGANIC COMPOUNDS
Organoplatinum Compounds - chemistry
Platinum - chemistry
PROPERTIES
Quantum Theory
Surface physical chemistry
THIOPHENE
Thiophenes
Thiophenes - chemistry
Ultraviolet
Wave functions
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Summary: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.
ISSN:1463-9076
1463-9084
DOI:10.1039/c2cp42700a