TOF-SIMS and Auger studies of ozone oxidation of unsaturated self assembled monolayers on silicon surfaces
EMSL Project ID
12890
Abstract
It has been recognized for decades that dust storms can lead to the global distribution of airborne mineral oxide particles,1 and that these can have an impact on climate as well as the chemistry of the atmosphere.2 One important facet of these particles is their ability to adsorb organics. Current thinking in the atmospheric chemistry community is that unoxidized organics will initially be taken up on these particles and that water will not readily be taken up on these hydrophobic surfaces. However, upon oxidation, the organic surface will become hydrophilic and take up water readily. This would enhance the ability of dust particles to act as cloud condensation nuclei, for example, changing the manner in which they contribute to global climate processes. The enhancement of a water film on the surface will also lead to increased uptake of atmospheric trace gases, potentially perturbing the gas phase chemistry. For example, enhanced HONO concentrations have been observed in Phoenix during a dust storm.3 We have been carrying out studies of the oxidation of self-assembled monolayers (SAMs) of unsaturated organics on silica using ozone. In a paper published recently,4 we showed that the oxidation by ozone of a SAM with a terminal double bond was rapid and formed at least in part, carboxylic acid functional groups on the surface. An unusual Langmuir-type of kinetics was observed in which O3 first rapidly adsorbs on the surface and then subsequently reacts with the double bond.
However, in a more recent set of unpublished studies, we do not find enhanced water uptake on the oxidized SAMs, a quite unexpected finding. More interesting, AFM studies show the formation of "balls" of material on the surface after reaction. We hypothesize that these are aggregates of polymeric material formed by the reaction and that they contain C,H and O. However, since they are formed from the oxidation of the monolayer, the underlying surface must now be silica that becomes exposed when the SAM that was originally attached to it is integrated in the organic balls on the surface. We see a structure to the underlying surface using AFM that would be consistent with this interpretation but the "coup de grâce" is a compositional scan of the surface. If this can be done with sufficient resolution, it should show areas with C, H and O sitting on an underlying SiOx surface. Discussions with Dan Gaspar and with Scott Lea suggest that TOF-SIMS and Auger may provide these data.
We therefore propose to bring samples we will prepare in our labs to EMSL to carry out TOF-SIMS and Auger. These samples will be Si substrates with unoxidized as well as oxidized SAMs on them, and for reference the bare substrate.
REFERENCES
(1) Prospero, J. M.; Charlson, R. J.; Mohnen, V.; Jaenicke, R.; Delany, A. C.; Moyers, J.; Zoller, W.; Rahn, K. 1983, 21, 1607.
(2) Finlayson-Pitts, B. J.; Pitts, J. N., Jr. Chemistry of the Upper and Lower Atmosphere - Theory, Experiments, and Applications; Academic Press: San Diego, 2000.
(3) Wang, S. H.; Ackermann, R.; Spicer, C. W.; Fast, J. D.; Schmeling, M.; Stutz, J. 2003, 30.
(4) Dubowski, Y.; Vieceli, J.; Tobias, D. J.; Gomez, A.; Lin, A.; Nizkorodov, S. A.; McIntire, T. M.; Finlayson-Pitts, B. J. 2004, 108, 10473.
Project Details
Project type
Exploratory Research
Start Date
2005-02-01
End Date
2007-07-06
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Mcintire TM, AS Lea, DJ Gaspar, N Jaitly, Y Dubowski, Q Li, and BJ Finlayson-Pitts. 2005. "Unusual aggregates from the oxidation of alkene self-assembled monolayers: a previously unrecognized mechanism for SAM ozonolysis?." Physical Chemistry Chemical Physics. PCCP 7:3605-3609.
T. M. McIntire, O. S. Ryder, P. L. Gassman, Z. Zhu, S. Ghosal, and B. J. Finlayson-Pitts, ?Why Ozonolysis May Not Increase the Hydrophilicity of Particles.? Atmospheric Environment, 44(7), 939-944 (2010). DOI: 10.1016/j.atmosenv.2009.11.009
T. M McIntire, S. R. Smalley, J. T. Newberg, A. S. Lea, J. C. Hemminger, and B. J. Finlayson-Pitts, 2006. “Substrate Changes Associated with the Chemistry of Self-Assembled Monolayers on Silicon.” Langmuir 22: 5617-5624. Langmuir 2006, 22, 5617-5624.
Yu, Y., Alexander, M. L., Perraud, V., Bruns, E. A., Johnson, S. N., Ezell, M. J. and Finlayson-Pitts, B. J. 2009. "Contamination from electrically conductive silicone tubing during aerosol chemical analysis", Atmospheric Environment, 43: 2836 (2009) doi:10.1016/j. atmosenv.2009.02.014