Influence of tip geometry in light emission from the scanning tunnelling microscope

In the scanning tunnelling microscopy of metal surfaces, electrons tunnelling inelastically emit light via the decay of coupled plasmons of the tip and the sample. We present an experimental study of the influence of the tip shape in light emission for a double tip system which is specially suitable to isolate the influence of the tip shape from other features in fluorescence spectra. Model calculations for various tip shapes show qualitative agreement with the experimental features, emphasizing the importance of tip shape in light emission.