Dose rate effect on bimetallic gold-palladium cluster structure

Radiolytic synthesis of mixed Au-III/Pd-II solutions at different dose rates is examined. The evolution of the plasmon spectra and the local X-ray micro diffraction has been systematically studied as a function of irradiation dose and dose rate. At low dose rate, a bilayered cluster of Au core-Pd shell is characterized. Due to intermetal electron transfer from nascent Pd atoms to gold ions, the latter are reduced first and constitute mainly the core of the particle, Pd ions being finally reduced at the surface of gold clusters when all Au-III ions have been reduced. In contrast, at high dose rate when the ion reduction is sudden and faster than a possible inter-metal electron transfer, it is shown by UV-vis spectroscopy, XPS, and EDAX results that genuine alloyed clusters are formed.