Spatially resolved detection of plasmon-enhanced fluorescence using scanning tunneling microscopy

We have measured a nanoscale fluorescence image of copper phthalocyanine (CuPc)/Au nanostructures on an indium tin oxide (ITO) substrate using a scanning tunneling microscope (STM). The quantum efficiency (QE) of the intrinsic fluorescence of CuPc is very low, however, the plasmon enhancement effect on an Au surface increases fluorescence efficiency. To obtain the nanoscale fluorescence image, in this study, we used up-conversion fluorescence through a triplet-triplet annihilation (TTA) process. Tunnel electrons induced fluorescence and tip-induced plasmon (TIP) emission simultaneously, however, the up-conversion fluorescence from CuPc could be clearly separated from TIP emission by spectroscopic filtering. The TIP showed different properties between the ITO substrate and the Au surface, and the CuPc fluorescence was enhanced only on the TIP of Au nanostructures. This study would lead to the application of a new fluorescence imaging method based on plasmon-assisted STM-induced light emission (STM-LE). Copyright (C) 2008 John Wiley & Sons, Ltd.