SURFACE SCIENCE AND ADSORBATE PHOTOCHEMISTRY

Simon J. Garrett Assistant Professor  (b. 1964). B.Sc., 1986, University of Sussex (U.K.); Ph.D., 1991, Imperial College of Science and Technology (U.K.); Postdoctoral Fellow, 1991-1993, Northwestern University; Postdoctoral Fellow, 1993-1996, University of Toronto. Surface Science and Adsorbate Photochemistry (organization of molecular monolayers, self-assembly, photochemistry and dynamics in the adsorbed state, photon- and electron-stimulated desorption). 517-355-9715, Ext. 208 garrett@cem.msu.edu

The study of solid surfaces impacts upon many aspects of our chemical world: corrosion, heterogeneous catalysis, chemical sensing, and semiconductor device fabrication for example. Organic monolayers adsorbed on surfaces are becoming increasingly important since their chemical and physical properties can be tailored in a relatively straightforward manner. Furthermore, the highly-ordered monolayers of molecules that usually result from adsorption on crystalline solids are ideal environments in which to investigate chemistry since the initial conditions are often well characterized and subsequent reactions are expected to be exquisitely sensitive to the molecular arrangement in the layers.

Research in this group is focused on understanding the photochemical reactions of organic monolayers, especially those containing unsaturated molecules. In theory, the use of photons offers the potential for control of specific bond activation. Additionally, the incorporation of unsaturated groups also allows little-studied surface chain reactions (polymerization) to occur.

Current research projects include a fundamental study of the reactions and photochemical behavior of formaldehyde (H₂C=O) adsorbed on copper single-crystals. The copper surface appears to act as a catalyst for the polymerization reaction in this case and spontaneous polymer formation is observed even at very low surface temperatures. We also study photochemistry in modified self-assembled alkane thiol monolayers on gold. These molecules have been modified to incorporate a variety of unsaturated groups which can be activated by photons. Crosslinking reactions in these systems should produce tough and durable monolayer films. A third research area is atmospheric particulate surfaces. Currently we are interested in the photochemical reactions of fluoro- and hydrofluorocarbon molecules on model soot surfaces. These molecules are replacements for ozone-depleting chlorofluorocarbons (CFC's) and may interact with atmospheric aerosols in the presence of UV light. The products of these reactions could be just as potent as those from CFC's.

We use many surface-sensitive spectroscopic tools in ultrahigh vacuum (UHV) (10^-13 atm) to examine the organization, electronic structure and chemical composition of the films. These techniques include x-ray and UV photoelectron spectroscopy (XPS and UPS), low energy electron diffraction (LEED) and temperature programmed desorption (TPD). A high resolution electron energy loss spectrometer (HREELS) is used to determine the adsorbate vibrational spectrum and a scanning tunneling microscope (STM) is used to image these systems with atomic resolution.

Students in this group learn surface chemistry and surface science techniques in a cross-discipline environment (analytical/physical/materials/surface chemistry).

Representative Publications

Photochemistry of Adsorbed Molecules. XVIII. Photodissociation and Exchange Reaction in CH₃Br/MgO(001) at 193 nm, S. J. Garrett, D. V. Heyd, and J. C. Polanyi, J. Chem. Phys., 106, 7847 (1997).

Photochemistry of Adsorbed Molecules. XVII. Photodissociation at 193 nm of CH₃Br adsorbed on LiF(001) and NaCl(001), S. J. Garrett, D. V. Heyd, and J. C. Polanyi, J. Chem Phys., 106, 7834 (1997).

The Photochemistry of CD₃I Adsorbed on the TiO₂(110) Surface, V. P. Holbert, S. J. Garrett, P. C. Stair, and E. Weitz, Surf. Sci., 346, 189 (1996).