Topography Dependence of Tunneling-Induced Fluorescence from Porphyrin Film

Abstract

We have measured spatially and spectrally resolved molecular fluorescence for H2TBPP film on Au excited by a scanning tunneling microscope (STM) in an ultrahigh vacuum (UHV) system. The tunneling-induced photon intensity map thus obtained shows a similar contrast to the STM grey-scale topography image, and indicates that the stronger tunneling luminescence comes from the higher topographies in STM image. This correlation is the same as the previously-reported correlation between the photon map of plasmon-mediated light emission for pure gold and its topography. This result supports the mechanism of surface-plasmon enhanced molecular fluorescence (SEMF), i.e., tunneling-electrons-induced molecular fluorescence in organic film is enhanced by the surface plasmons.