AVS 47th International Symposium
    Organic Films and Devices Wednesday Sessions
       Session OF-WeA

Paper OF-WeA10
Self-assembled Monolayers of 6-Phenyl-n-Hexanethiol and 6-(p-Vinylphenyl)-n-Hexanethiol on Au: An Investigation of Structure, Stability and Reactivity

Wednesday, October 4, 2000, 5:00 pm, Room 313

Session: Self-Assembled Monolayers: Electron Transfer and Film Properties
Presenter: L. Duan, Michigan State University
Authors: L. Duan, Michigan State University
S. Garrett, Michigan State University
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The structure, stability and reactivity of 6-Phenyl-n-Hexanethiol (PHT) and 6-(p-Vinylphenyl)-n-Hexanethiol (VHT) monolayers on Au (111) is presented. RAIR spectroscopy, ellipsometry and STM have been used to characterize the self-assembled monolayers (SAMs). The RAIR spectral data indicated that both molecules chemisorbed on gold as thiolates, however, the alkyl chains were disordered for both SAMs. We investigated the structural changes of PHT monolayers with decreasing molecular surface density by annealing in ultrahigh vacuum. Three different "stripe" phases have been observed by STM. All three condensed phases are characterized by alignment of the molecular axes with the surface plane, but with decreasing degrees of out-of-plane interdigitation. On the contrary, VHT molecules are oriented almost parallel to the surface normal at room temperature. Polymerization of VHT SAMs can be achieved by either UV-light irradiation or annealing. The polymerization process was followed by RAIR spectroscopy by observing the decrease in peak intensities associated with vinyl functionalities. UV-light irradiation produced long chain polymers with ~70% conversion rate after 25 min, while annealing produced short-chain polymers with CH@sub 3@ as the end group. The UV-light polymerized film is more robust to heating than thermally polymerized film.