Concurrent mechanical and surface electronic responses in electrochromic metal oxide thin films

Electrochromic metal oxide thin films exhibit ion-driven optical switching, but their accompanying mechanical and surface electronic responses remain insufficiently understood. In this work, we investigate sputtered WO₃ and NiO electrochromic films using an approach combining electrochemical analysis, nanoscale mechanical mapping and surface potential characterization. Cyclic voltammetry (CV) and chronoamperometry (CA) confirm reversible charge storage with characteristic optical modulation. Atomic force microscopy (AFM) force–displacement measurements reveal a consistent increase in DMT modulus upon charging associated with Li⁺ insertion, and a decrease upon discharging, indicating reversible electrochemo-mechanical coupling in both materials. Surface morphology evolves modestly across redox states. Kelvin Probe Force Microscopy (KPFM) mapping further shows contact potential difference (CPD) shifts that align with work function modulation during electrochemical cycling. Notably, the observed increase in surface potential in the charged state may help explain the asymmetry in electrochromic response times, with longer charging times linked to higher work function barriers. This integrated mechanical–electrochemical–electronic research provides new insights into the structure–function relationship of electrochromic oxides and informs the design of durable and responsive smart material systems.