Shoshanna Coon

My research centers on the chemistry that occurs on surfaces. Any heterogeneous chemical reaction actually takes place at the interface between two phases. Therefore, an understanding of the mechanisms of these reactions requires knowledge of the surface characteristics and the interactions of the surface with the other phase.

Surface chemistry is important in many fields of technological importance, including corrosion prevention, heterogeneous catalysis, thin films and coatings, friction and wear, and semiconductor device manufacture.

I am specifically interested in the surface chemistry of solids, especially salts and oxides. Much of the work in surface chemistry has been done on metal surfaces. The interactions of molecules with salt or oxide surfaces will be significantly different than with a metal because of the localization of opposite charges on the surface. Thus, one aspect of the research is the characterization of the adsorption of molecules on a surface and how the surface properties affect the adsorption.

However, it is the chemistry that adsorbed molecules undergo on the surface that I am most interested in. Thermally driven bond cleavage can be enhanced by the adsorption of molecules onto a surface, because the molecular fragments may have a stronger interaction with the surface than the original molecules. If the necessary energy to break bonds is supplied thermally, the surface can provide a new pathway to reaction that is not available in the pure substance.

These surface species may be intermediates in the formation of another molecule which is yet more stable. This process is the basis for catalysis, in which the rate of the reaction is enhanced by the presence of another substance, the surface in this case.

A very exciting newer area of research is the photochemistry of molecules on surfaces. Since photochemical reaction pathways are often different than thermal pathways, photoexcitation of molecules on surfaces provides yet another possibility for accomplishing a desired reaction. Some changes in the wavelength dependence of photochemistry have been seen for molecules adsorbed onto metal surfaces, due to photoexcitation of metal electrons.

While this mechanism is not expected for electrically insulating surfaces, photochemistry of molecules on semiconducting transition-metal oxides promises to be a rich area of study.