Research

In the last few years, our detailed interest has been in three directions: (1) understanding surface and thin film processes, (2) investigating nanoscale dynamics in metallic alloys using coherent x-ray scattering, and (3) studying the relationship between atomic structure and function in solid oxide fuel cell cathodes. Many of our in-situ studies utilize a unique ultra-high vacuum growth and surface modification facility that we developed in collaboration with Randall Headrick (University of Vermont) on the insertion-device beamline X21 at the NSLS. We have used it to examine nanoscale patterning during ion bombardment in collaboration with the Aziz group (Harvard University) and others, issues related to the growth of wide-bandgap group III-V semiconductor films using plasma-assisted molecular beam epitaxy (PA-MBE), and fundamental growth kinetics during sputter deposition and evaporation. In collaboration with the groups of Christophe Detavernier (University of Ghent, Belgium) and Charles Eddy (Naval Research Laboratory) we have also been investigating the kinetics of growth by atomic layer deposition (ALD) and atomic layer epitaxy (ALE).

Coherent X-Ray Scattering

Coherent x-ray scattering provides the ability to probe nanoscale dynamics in metallic alloys and other materials systems. Partially coherent x-ray beams are created using small (10 micron) slits in conjunction with a high-brilliance 3rd generation synchrotron source, such as the APS. The disorder in the alloys produces speckle patterns in the scattered x-ray intensity. The evolution of the speckle pattern can then be related to the underlying dynamics of structural changes (e.g. ordering, phase separation or stacking fault rearrangement) in the alloy. In collaboration with the Headrick group we have recently undertaken the first coherent grazing-incidence small-angle X-ray scattering (GISAXS) studies of thin film growth, probing fundamental surface morphology dynamics during sputter deposition at the APS.

Cathode Materials

Solid oxide fuel cells offer the potential for highly efficient energy conversion, but improvements in cathode function are needed before their potential can be fully realized. In collaboration with Profs. Pal, Basu and Gopalan in Engineering and Prof. Smith in Physics, we are examining the near-surface atomic structure of cathode materials in-situ to better understand the relationship between function and structure.