Pt thin film transient mobility over yttria stabilized zirconia

Platinum thin films cover supports like yttria stabilized zirconia, titanium dioxide and graphite as a precursor to create catalysts and electrodes with micro- and nanostructures that improve their reactivity. Due to the difference of free energy per area between a thin film and agglomerated particles, Pt migrates when annealed above 400 °C, thus forming three-phase boundaries. Kinetic studies based on temperature demonstrated that holes form first. As the holes grow larger, bridges form between Pt domains and finally break leaving isolated islets. Here we report how Pt thin films (15 nm to 30 nm-thick) morphology evolves as a function of both temperature (550 °C to 1000 °C) and time (up to 16 h). Starting from a 30 nm-thick film, the support uncovered area and islet diameter reach respectively a maximum and a minimum at 12 h when annealed at 700 °C. We show that beyond this time islets are coarsening, the platinum reforms bridges, the uncovered area and the particle height decrease. The transition time is only 4 h for 15 nm and 700 °C and it is less than 8 h for 30 nm and 1000 °C.