Observation of the enhancement of the electric field normal to the surface of mid-infrared slot antennas

After growing a thin Al₂O₃ layer by atomic layer deposition on a Si substrate, slot antenna arrays were formed on it. Reflectivity spectra measured in the mid-infrared range showed characteristic aspects, presumably caused by the surface phonon polariton of a SiO₂ layer naturally formed on the Si substrate. When the Al₂O₃ layer thickness was 6 nm, such spectral features disappeared. In this way, we could estimate experimentally the electric field distribution normal to the surface of the substrate.