Scanning Tunneling Optical Microscopy (Stom) of Silver Nanostructures

Local photon emission properties in the visible range of granular and island silver films have been characterized using STM. The experimental data are discussed in the light of model calculations. The observed fluorescence spectra and their dependence on tunnel voltage are interpreted theoretically in terms of radiative decay of local surface Plasmons excited dominantly via inelastic tunneling. Spatial mapping of the resulting integrated light intensity (photon maps) reveals a close relation to topographic features. The sharp spatial contrast, lack of significant polarity dependence, and the detection of fieid emission resonances in isochromat photon spectra favor inelastic tunneling as the dominant process.