Developing relationships between the structure and reactivity of adsorbed species is the primary focus of our research program. We currently emphasize in-situ methods for studying the bonding and reactivity of adsorbed species, hydrocarbon oxidation on platinum surfaces, the properties of polymer surfaces and microfabricated chemical sensors.

We pioneered the development of Fluorescence Yield Near-Edge Spectroscopy, or FYNES, in the ultra soft X-ray region above the C, O, and N K-edges as an in-situ method for characterizing adsorbed species and surface reactions. A powerful combination of soft X-ray method capable of determining intermediate concentrations, C-H stoichiometries, and the bonding of adsorbed species has been developed over the past several years. These methods are being developed further and used to characterize a range of interesting surface reactions. PRT membership in the U7A soft X-ray beam line at Brookhaven’s National Synchrotron Light source has provided regular access to state of the art facilities with improved flux and energy resolution. Improved detectors based on solid state diodes and multilayer mirrors promise to further enhance our ability to perform rapid high-resolution kinetic experiments on monolayers. We are part of a new undulator initiative at the Advance Light Source which will provide access to soft X-ray microscopy facilities with micron resolution, to in-situ surface analysis facilities which can be used at substantially higher pressures and to facilities with improved time resolution. This program is a collaboration with Dr. Fischer from NIST.

The study of the catalytic oxidation of unsaturated hydrocarbons provides valuable information about these important surface reaction mechanisms. We are investigating both partial oxidation on metals like silver and gold and on deep oxidation on metals like platinum and palladium. These reactions are being studied on surfaces ranging from simple model single crystal surfaces, more complex single crystal surface with large defect concentrations, even more complex discontinuous supported thin film surfaces, and on optimized nano-particulate catalysts on high surface area supports. These pioneering studies are revealing the molecular mechanisms of key reaction steps during both transient and steady state catalytic oxidation. Recent in-situ studies on the Pt(111) surface have revealed that during steady state propylene oxidation the primary surface intermediate is methylacetylene even in large excesses of oxygen. The structure and bonding of this interesting intermediate has been characterized using a combination of soft X-ray methods. Studies with propylene partial oxidation catalysts composed of silver supported on titania have revealed that a previously unknown, strongly adsorbed form of rehybridized propylene is formed on the perimeter of these supported silver particles.

The complexity and molecular nature of polymer surfaces makes characterization of both the surface structure and reactivity of polymer surfaces especially challenging. The soft X-ray methods we have developed promise to offer an important new perspective on characterization of many types of polymer surfaces. Understanding chemical interactions with polymer surfaces plays a key role in the development of important new technologies ranging from microelectronic devices to chemical sensors. We are currently focussing our attention on the interactions of reactive gases and metals with several classes of polymer surfaces. Two dimensional polymers systems and ultra-thin polymer films offer exciting opportunities for development of materials where designed surfaces dominate materials properties. We are currently studying the interaction of low valent metals with a novel polydiacetylene and polyimidazole thin films as part of our efforts to develop a foundation of understanding for new catalysts and chemical sensors. These efforts are collaborations with the groups of Professor Rasmussen and Professor Evans.

The development of microfabricated chemical sensors based on modular arrays of supported nanoparticulate metal films is the primary focus of our chemical sensor program. Surface chemistry concepts play a key role in optimization and design of stable, chemically selective sensor films. Chemical modification of Pt films, with coadsorbed species like S and Au, is being used to tailor chemisorption strengths and oxidation activation energies to promote chemical selectivity. Currently, our effort to detect oxygen in reactive ion etching feed gases are centered on understanding and optimizing conductometric response in Pt/Al₂O₃ and Pt/TiO_2-x discontinuous sensing films. This research is a collaboration with the group of Professor Schwank.

1993 Manos Mavrikakis (ChE) Kinetically Coupled Surface and Bulk Processes

1993 Tecle Rufael (Chem) H Induced C-S Bond Activation on Platinum and Nickel

1993 Elizabeth Slaughter (Chem) Gallium Nitride Growth on GaAs

1995 Sean Huang (Chem) H Induced C-N Bond Activation on Platinum and Nickel

1996 Kyung-Ah Son (Chem) H Induced C-C Bond Activation on Nickel

1997 Robin Merchant (ChE) Sensing Films for Aromatic Detection

1997 Aleks Franz (ChE) Hydrogen Energetics and Transport in Amorphous Silicon

1998 Jeff Ranney (ChE) Propylene Partial Oxidation on Modified Silver Surfaces

1998 Valarie Thomas (ChE) Chemical Modification of Platinum Sensing Films

1998 Sean Kane (Chem) Carbon-Sulfur Bond Activation on Platinum and Nickel

1999 Adam Capitano (Chem) Hydrogen Radical Induced Bond Activation in Organics

2000 Aaron Gabelnick (Chem) C₃ Hydrocarbon Oxidation Mechanisms on Platinum Surfaces

(2001) Dan Burnett (ChE) Hydrocarbon Oxidation on Platinum Crystal, Thin Film and

Cataylst Surfaces

(2002) Andy Marsh (Chem) Interactions with Polymer Surfaces

(2002) Henry Lewis (ChE) Oxidation Mechanisms on Stepped Platinum Surfaces

(2002) Marina Miletic (ChE) Modeling of Oxidation Reactions on Platinum Surfaces