Plasmon Resonances of Mid-IR Antennas on Absorbing Substrate: Optimization of Localized Plasmon-Enhanced Absorption upon Strong Coupling Effect

We report on the surface plasmon resonances of mid-infrared Au antennas deposited on an absorbing silicon-rich oxynitride (SRON) thin film, and on their utilization for enhancement of a spatially localized absorption of infrared (IR) radiation in SRON. The antenna resonances were experimentally determined from far-field IR reflection spectra measured over a broad mid-IR range. Due to a hybridization effect caused by the strong coupling of localized surface plasmon resonances with vibration modes, phonon resonances in SRON, these spectra show up the Rabi splitting of the reflection peaks, and thus, three hybrid branches where resonant wavelengths scale nonlinearly with the antenna length have become apparent. To maximize spatially localized plasmon-enhanced energy absorption in SRON, a compromise wavelength between that one related to optimum antenna resonances and the SRON resonant absorption wavelengths must be chosen. We stress that the principles of this method can be utilized in other dielectric or semiconductor materials resonantly absorbing in the mid-IR range, and, more generally, in other spectral regions, including the visible (e.g., due to excitons). Hence, in addition to the spatially localized heating, the principles can be exploited in an optimization of the efficiency of IR and light detectors, solar cells, biosensors, and other applications