Inelastic tunneling excitation of tip-induced plasmon modes on noble-metal surfaces

Light emission characteristics from the tunnel gap of a scanning tunneling microscope are used to elucidate the interaction of tunneling electrons with tip-induced plasmon modes on Ag, Au, and Cu surfaces. Enhanced redshifted spectra are observed in the tunneling regime. Model calculations of optical spectra in this range agree well with the experimental data. Isochromat spectra are used to demonstrate that the principal excitation process occurs via inelastic tunneling. © 1991 The American Physical Society.