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Issue 20, 2005
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Unusual aggregates from the oxidation of alkene self-assembled monolayers: a previously unrecognized mechanism for SAM ozonolysis?

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Abstract

Self-assembled monolayers (SAMs) of vinyl-terminated 3- and 8-carbon compounds were generated on Si substrates and reacted at room temperature with ∼1 ppm gaseous O3. A combination of atomic force microscopy (AFM), scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to study the surface composition and morphology after oxidation. A distribution of large (∼0.1–10 μm) organic aggregates was formed, while the surrounding substrate became depleted of carbon compared to the unreacted SAM. This highly unusual result establishes that the mechanism of ozonolysis of alkene SAMs must have a channel that is unique compared to that in the gas phase or in solution, and may involve polymerization induced by the Criegee intermediate (CI). Oxidation at 60% RH led to the formation of a number of smaller aggregates, suggesting water intercepted the CI in competition with aggregate formation. The uptake of water, measured using transmission FTIR, was not increased upon oxidation of these films. In conjunction with literature reports of polymer formation from VOC-NOx photooxidations, these results suggest that formation of aggregates and polymers in the atmosphere is much more widespread than previously thought. The implications for the ozonolysis of alkenes on surfaces, for the transformation of organics in the atmosphere, and for the reactions and stability of unsaturated SAMs, are discussed.

Graphical abstract: Unusual aggregates from the oxidation of alkene self-assembled monolayers: a previously unrecognized mechanism for SAM ozonolysis?

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Publication details

The article was received on 09 Jun 2005, accepted on 18 Jul 2005 and first published on 30 Aug 2005


Article type: Paper
DOI: 10.1039/B508147E
Citation: Phys. Chem. Chem. Phys., 2005,7, 3605-3609
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    Unusual aggregates from the oxidation of alkene self-assembled monolayers: a previously unrecognized mechanism for SAM ozonolysis?

    T. M. McIntire, A. Scott Lea, D. J. Gaspar, N. Jaitly, Y. Dubowski, Q. Li and B. J. Finlayson-Pitts, Phys. Chem. Chem. Phys., 2005, 7, 3605
    DOI: 10.1039/B508147E

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