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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 30, Number 8
BKCSDE 30(8)
August 20, 2009 

Comparative Study of Tetrahydrothiophene and Thiophene Self-Assembled Monolayers on Au(111): Structure and Molecular Orientation
Eisuke Ito*, Masahiko Hara, Kaname Kanai, Yukio Ouchi, Kazuhiko Seki, Jaegeun Noh*
Near-edge X-ray absorption fine structure, Self-assembled monolayer, Thiophene, Tetrahydrothiophene, Molecular orientation
Surface structure and molecular orientation of self-assembled monolayers (SAMs) formed by the spontaneous adsorption of tetrahydrothiophene (THT) and thiophene (TP) on Au(111) were investigated by means of scanning tunneling microscopy (STM) and carbon K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy. STM imaging revealed that THT SAMs have a commensurate (3 × 2√3) structure containing structural defects in ordered domains, whereas TP SAMs are composed of randomly adsorbed domains and paired molecular row domains that can be described as an incommensurate packing structure. The NEXAFS spectroscopy study showed that the average tilt angle of the aliphatic THT ring and π-conjugated TP ring in the SAMs were calculated to be about 30o and 40o, respectively, from the surface normal. It was also observed that the π* transition peak in the NEXAFS spectrum of the TP SAMs is very weak, suggesting that a strong interaction between π-electrons and the Au surface arises during the self-assembly of TP molecules. In this study, we have clearly demonstrated that the surface structure and adsorption orientation of organic SAMs on Au(111) are strongly influenced by whether the cyclic ring is saturated or unsaturated.
1755 - 1759
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