Mechanical Stretching Induced Highly Tunable and Reversible Mid-infrared Plasmonic Resonances in a Conductive Polymer...

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.