Mechanical Stretching Induced Highly Tunable and Reversible Mid‐infrared Plasmonic Resonances in a Conductive Polymer Thin Film

Abstract Mid‐infrared plasmonic resonance enables nanoscale light confinement at mid‐infrared frequencies, leading to various applications ranging from compact infrared lasers to biological and chemical sensing. However, upon fabricated, plasmonic resonators normally have a fixed resonance frequency, which limits their application frequency range and hinders the dynamic tuning potential. Here, with the flexible PEDOT:PSS ((poly(ethylenedioxythiophene):poly(styrenesulfonate)) conducting polymer as the plasmonic medium, highly tunable and reversible mid‐infrared plasmonic resonances are demonstrated via mechanical stretching. Such plasmonic resonances, based on the stretching‐induced grating‐type morphology of the PEDOT:PSS thin‐film, can be readily tuned across a large mid‐infrared frequency range from ≈7500 to 1500 cm⁻¹. In addition, the stretching‐induced plasmonic resonances are well reversible in a recovery process and reproducible under 1000 stretching‐recovery cycles. Furthermore, the stretching‐induced plasmonic resonances also show the mid‐infrared chemical sensing ability by enabling surface‐enhanced infrared absorption of molecular moieties. The work paves a new way for the active tuning of mid‐infrared plasmonic resonances, and will promote the development of flexible mid‐infrared plasmonic devices.