Electric field distribution perpendicular to the surface of mid-infrared antennas

The electric field in the normal direction was experimentally investigated by using mid-infrared antennas that were formed on a thin Al₂O₃ layer/Si substrate. The Al₂O₃ layer could be as thin as a single nm-order employing the atomic layer deposition, and was varied from 2 nm to 50 nm. The field distribution was estimated by observing the reflectivity change. It was found that the electric field decreased rapidly until a 6 nm depth from the antenna plane, and that the degree of attenuation became relaxed in the deeper region.