Nanoscale Excitation Mapping of Plasmonic Patch Antennas

We experimentally investigate the resonant modes of plasmonic patch antennas using angle-resolved cathodoluminescence imaging spectroscopy. Plasmonic modes residing in the patch antenna are locally excited using a scanning electron beam, providing high-resolution spectral and spatial maps of the modes of patch antennas corresponding to variations in the local density of optical states in the antennas. A semianalytical model is used to qualitatively explain the experimentally observed modes. Furthermore, emission patterns, directionality, and beam steering properties of patch antennas are studied in different patch sizes and at different wavelengths. Strong directionality and control over the output beam angle as a function of excitation position are observed. A distributed dipole model is used to explain the radiation pattern and beam width of the patch antenna radiation, which shows a good agreement with experiment.