Mapping surface plasmons at the nanometre scale with an electron beam

The optical response from metal nanoparticles and nanostructures is dominated by surface plasmon generation and is critically dependent on the local structure and geometry. Electron energy-loss spectroscopy (EELS), combined with recent developments in spectrum imaging and data processing, has been used to observe the energy and distribution of surface plasmons excited by fast electrons. The energy of the plasmon responses is consistent with the optical response and with calculations. For gold and silver rods and ellipsoids, longitudinal, transverse and distinct cluster modes were readily identified and mapped. The spatial resolution of the presented maps is one order of magnitude better than that achievable with scanning near-field optical microscopy (SNOM)-based techniques.