  We investigated the localized electronic properties of nanoporous gold films
by using an ultra-high vacuum scanning tunneling microscope at low temperature
(4.2 K). Second derivative scanning tunneling spectroscopy shows the plasmon
peaks of the nanoporous gold films, which are excited by inelastic tunneling
electrons. We propose that the nanorod model is appropriate for nanoporous gold
studies at the nanometer-scale. These results are supported by a 3D electron
tomography analysis and theoretical calculations of nanoporous gold with
ellipsoid shape.
