Cathodoluminescence investigation of the Ge nanoantenna: (a) top-view scanning electron microscopy images of the investigated nanoantenna (the dashed line represents the trajectory of the scanning electron beam during the acquisition of the cathodoluminescence spectra); (b) two-dimensional map (emission wavelength as a function of the electron beam position along the antenna axis) from the cathodoluminescence investigation, with solid white lines representing the intensity profile integrated over a wavelength range of about 50 nm around each resonance; (c) smoothened cathodoluminescence spectra acquired at specific positions (marked with letters a-m on panel b) along the antenna axis, after vertical translation for sake of readability; (d) raw data for the smoothened cathodoluminescence spectra of panel c.