Piezoresponse in WO₃ Thin Films Enhanced by Pt-Nanoparticles as Revealed by Atom Probe Tomography and Cs-Transmission Electron Microscopy

Tungsten trioxide (WO₃) is an intrinsic n-type semiconductor that can be prepared to exhibit a piezoresponse through doping and heat treatment strategies. We report the piezoresponse in platinum-doped WO₃ thin films, prepared by RF/DC cosputtering, followed by postdeposition annealing at 600 °C. Measurements using Switching Spectroscopy Piezo Force Microscopy (SS-PFM) reveal domains with different polarization orientations and hysteresis behavior, corresponding to a piezoelectric coefficient of d₃₃ = 97 ± 6 pmV^-1. Low-angle x-ray diffraction (XRD) indicates the presence of an orthorhombic structure (β-WO₃) with a Pbcn space group, while Scanning Transmission Electron Microscopy (STEM) reveals the formation of platinum nanoparticles (∼5 nm) with a cubic structure (Fm(Formula presented)m). Atom Probe Tomography (APT) confirms the formation of Pt nanoparticles and Ar-enriched cavities within the WO₃ matrix induced by the annealing process. These structural modifications create lattice strain, giving rise to piezoelectric domains with different polarization orientations.