An extraordinary number of environmentally and technologically important processes can be traced to chemical reactions occurring at a surface. Heterogeneous catalysis, chemical vapor deposition, corrosion, adhesion, ozone depletion, electrochemistry: all of these phenomena have in common the fact that they require a chemically reactive surface. My students and I explore the mechanisms of surface chemical reactions, especially those at the gassolid interface. Areas of current research activity include: (i) the surfaces of cloud particles and their importance in atmospheric chemistry, and (ii) the use of gaseous precursors for the selective deposition of technologically important materials, such as diamond and aluminum.

It proves to be advantageous to study gas-surface interactions under highly idealized conditions. We conduct our experiments in specially designed reaction chambers that operate at pressures of approximately 10-13 atmospheres. Samples are carefully prepared so that surface structure is relatively well understood. Finally, the gas phase composition is carefully monitored and controlled.

Chemical reactions that occur in the surface and near surface regions of cloud particles have been shown to participate in the sequence of events that ultimately opens the stratospheric ozone hole. Among the particles understood to be important are those composed of ice and sulfuric acid, substances which my laboratory is well equipped to study. My students and I employ a number of experimental methods to study reactions at these surfaces. Adsorbate structure is investigated with infrared spectroscopy and x-ray photoelectron spectroscopy. For instance, we have obtained the vibrational spectra of acetonitrile on ice and chlorine dioxide on sulfuric acid. Reaction kinetics can be monitored as well, using techniques that are based upon mass spectrometry. We have shown from our kinetic studies that different allotropes of ice have different surface chemical properties, an observation that may have important implications for our understanding of cloud particle chemistry. An area of recent activity concerns the possibility that surface photochemistry is important in the atmosphere; currently we are examining photon-induced reactions of chlorine dioxide on ice.

Among the many methods that are employed to grow solid materials of technological import is one called chemical vapor deposition (CVD). In CVD, solid film growth occurs via the controlled decomposition of one or more gaseous precursors. For example, tungsten hexafluoride and hydrogen are used to deposit high purity tungsten films in certain microelectronics applications. CVD necessarily involves reactive steps that occur at a surface, and it is these steps we seek to study. We have completed studies of tungsten hexafluoride and titanium tetrachloride on tungsten; currently we are investigating the decomposition of some industrially promising aluminum CVD precursors on a variety of surfaces. Another area of focus involves the use of methane as a precursor for diamond in a plasma-assisted CVD process. Many of techniques used to study the CVD systems are similar to those we employ in the cloud particle work. In addition, we employ diffraction and scanning probe methods to determine the structures of deposited films.

Students in my group are drawn from the physical, inorganic, materials, and analytical chemistry specialty areas of the department. This diversity of interests and background creates a stimulating mix of perspectives to scientific problems, which proves to be invaluable for complex, multidisciplinary systems like those we study.