Metamaterial plasmonic absorber for reducing the spectral shift between near- and far-field responses in surface-enhanced spectroscopy applications

The spectral shift between near- and far-field responses of the plasmonic nanoantennas has negative effects on the performance of surface-enhanced spectroscopy measurements. In order to reduce these effects, we propose use of the plasmonic absorber (PA) concept that promises lower spectral-shift between the near- and far-field responses. In this context, we present the design, characterization and experimental realization of a novel PA structure which utilizes hexagonally arranged nanoantennas operating in the mid-infrared regime. Additionally, we analyze the PA device numerically and experimentally to investigate tunability of resonant modes. To reveal the absorption mechanism, we investigate the near-field distribution maps in addition to the charge and current density distributions. With the aim of comparing the proposed PA device with the conventional particle-based nanoantenna according to the amount of spectral shift between the near- and far-field peaks, we present the near- and far-field spectra of each configuration and show that PA structure exhibits significantly lower spectral-shift. Finally, we present the effect of reduced spectral-shift on the surface-enhanced infrared absorption spectroscopy through the simulations for the detection of the molecular absorption mode of a polymer and compare with the results of particle nanoantenna configuration.