a, STEM-ADF image of a triangular Au nanoprism on a TiO2 particle. b, Experimental EELS spectra acquired using the electron beam locations marked in a: near the short edge (P1), the long edge (P2) and the short edge near TiO2 (P3). The centre (energy) and amplitude (intensity) of the LSP resonance peak are derived by fitting a Gaussian profile (see inset). c, Experimental EELS intensity map of the same Au nanoprism in a for the energy-loss range from 1.8 eV to 3.8 eV, confirming that the optimal electron beam location to excite LSP modes is at the cantilevered corner and several nanometres beyond in the vacuum. The EELS intensity is normalized to the zero-loss peak intensity to enhance the attenuated signal within the bulk of Au due to scattering and is therefore given in arbitrary units.