T. Proksch, M. Barbosa
North Carolina State University,
United States
Keywords: ion insertion, electrochromism, mechanical deformation, operando measurements, electrolyte-gated transistor
Summary:
WO₃ is a metal oxide semiconductor widely investigated for its electrochromic capabilities. Here, it has been employed as the channel material in an ion-gated transistors (IGT) using [EMIM][LiTFSI] as the liquid gating electrolyte. Because the ionic gating can be used to modulate carrier density in the WO₃ channel, the IGT platform provides a controlled platform for probing fundamental material behavior. During proton insertion, WO₃ undergoes reversible structural changes that produce mechanical deformation and optical color changes. In this work, the local mechanical responses are measured operando using atomic force microscopy (AFM). Comparisons between devices gated with doped and undoped ionic liquids confirm that the observed mechanical response originates from ion insertion. To complement these observations, we simultaneously employ optical characterization techniques to study ion insertion dynamics. Colorimetric analysis offers a quantitative approach to tracking local changes in optical properties that reflect underlying ionic motion and electronic structure evolution. These measurements reveal a strong correlation between the mechanical and optical signals, both of which vary spatially. This multimodal approach combining electrochemical, mechanical, and optical characterization enables direct correlation between local ion dynamics and global device behavior, offering a powerful means to investigate the fundamental properties of electrochromic materials.