Their research has benefited from the aberration-corrected scanning transmission electron microscopes (STEMs) at Lehigh as well as NIST. Lehigh was the first university in the world to acquire two of the instruments, whose aberration correctors greatly improve imaging resolution and chemical analysis capability by overcoming distortions in the lenses that tend to blur the electron beam.
In the current project, aberration-corrected STEMs at Lehigh and NIST were used to measure the composition and particle size distribution of the gold-palladium alloy, and to understand how they change with various acid-washing pretreatments.
The researchers employed several characterization techniques, including High-Angle Annular Dark Field (HAADF) imaging to measure the change in nanoparticle size and energy-dispersive x-ray (XEDS) analysis to determine the composition of individual alloy particles.
"Without the aberration-corrected STEMs, we would not have been able to unravel what was going on in this instance," says Kiely.
In addition to performing experiments on the gold-palladium catalyst, the researchers ran parallel control experiments on pure gold and pure palladium separately.
"We found it was important for the palladium to incorporate just a small amount of gold," says Kiely. "The gold appears to modify the electronic structure and thus the catalytic activity of the palladium.
|Contact: Kurt Pfitzer|