Gold‐Oxide Nanofilms Trigger Ultrafast, Reagent‐Free, Site‐Confined Growth of Conducting Polyaniline

ABSTRACT Conducting polymers enable the simultaneous transport of electrons and ions within soft, biocompatible matrices. Yet their synthesis typically relies on soluble oxidants that generate stoichiometric waste and inhibit high‐resolution patterning. Nanometer‐thick gold films deposited by direct‐current magnetron sputtering in dilute air function concurrently as a template and intrinsic oxidant—though, owing to their discontinuous structure, not as current collectors—for the reagent‐free growth of emeraldine‐salt polyaniline (PANI‐ES). X‐ray photoelectron spectroscopy reveals that freshly sputtered films contain approximately 60% Au 2 O 3 , which is quantitatively reduced by aniline within 60 s. In situ UV–vis spectroscopy records an increase in the 750 nm polaron band that scales linearly with oxide thickness. Polymerization self‐terminates once the local Au(III) reservoir is exhausted, yielding patterns precisely registered to the underlying metal mask. The resulting PANI‐ES retains the optical, Raman, and electrochemical signatures of the highly conductive emeraldine salt. By replacing soluble oxidants with a solid Au 2 O 3 underlayer, the process avoids sulfate‐containing solution‐phase by‐products and enables aniline‐to‐PANI conversion at room temperature under ambient air, providing a straightforward route to patterned PANI films without post‐growth wet lithography for hole‐transport layers, neural microelectrodes, and chemiresistors.