Role of polycrystalline F–SnO2 substrate topography in formation mechanism and morphology of Pt nanoparticles by solid-state-dewetting

Abstract

Solid-state-dewetting (SSD) of thin films is increasingly utilized to fabricate nanoparticles for catalysis. In-depth understanding of particle formation mechanism is crucial to control key properties of catalytic particles such as size, size distribution, and structure. In contrast to most studies on SSD of thin metal films on smooth substrates (e.g., SiO₂/Si, …), here we investigate how the topography of practical substrates, such as electrically conductive F-SnO₂ (FTO), affects the formation mechanism and size of Pt particles – with potential use as nanoparticle electrodes, e.g., in electrochemical conversion or sensing applications. For this, we combined in situ scanning transmission electron microscopy (STEM) with ex situ rapid thermal annealing (RTA) methodologies. Our results indicate that, by dewetting 5 nm of Pt films on FTO, the arrangement of Pt nanoparticles exhibits a bimodal particle distribution. This is driven by: (i) a thinner initial Pt film thickness in the “depths” of the FTO substrate due to shadowing effects, and (ii) the formation of varying surface curvatures in the Pt film, both caused the topography and grain structure of the FTO substrate. Particularly, the latter introduces an additional driving force for Pt diffusion from peaks and ridges (positive local curvature) to flat terraces (no curvature) and valleys (negative local curvature).