Mid-IR plasmonic antennas on silicon-rich oxinitride absorbing substrates: Nonlinear scaling of resonance wavelengths with antenna length.

We report on the resonant properties of platinum dipole antennas fabricated on a silicon-rich-oxinitride thin film that exhibits significant absorption in the mid-infrared of the electromagnetic spectrum (λ^-1≈1100 cm^-1). A nonlinear scaling between the resonant wavelength and the antenna length has been found and quantitatively confirmed by full-field electromagnetic simulations. The resonant wavelength increases linearly with antenna length for small lengths and tends to saturate for large ones (length >4 μm). This saturation effect is attributed to the coupling of a geometrical antenna resonance and an absorption resonance of the substrate material. [ABSTRACT FROM AUTHOR]