Mid-Infrared Localized Plasmons through Structural Control of Gold and Silver Nanocrescents

Metal nanoarchitectures producing optical responses in the visible and near-infrared form the foundation for most plasmonic studies. In contrast, a relative lack of infrared-active substrates has limited the exploration of plasmonic behavior beyond the near-infrared. In this study, we investigate the polarization-dependent, multimodal localized plasmon resonances of asymmetric nanocrescents for large diameter structures composed of gold and silver. The extended size (0.5-3.0 mu m) shifts the plasmon resonances into the mid-infrared (mid-IR) spectral range. Polarization-dependent localized surface plasmon resonance (LSPR) behavior is maintained for nanocrescent diameters up to several microns due to the preservation of nanoscale structural features that result in high aspect ratios. Simulations of the extinction spectra and near-field distributions support experimentally observed plasmonic behavior. Manipulation of nanocrescent plasmon resonances in the mid-IR spectral range through structural-based tuning and polarization control of incident light will find application in IR-related detection, light guiding, and surface-enhanced IR-based spectroscopies.