Light emission spectra of the monolayer-island of C60 molecules on Au(111) induced by scanning tunneling microscope

We have measured the light emission (LE) spectra of the ordered C-60 monolayer-island on the Au(111) surface and the bare An surface, induced by the scanning tunneling microscope (STM). The optical measurements were performed at 78 K using electrochemically etched W-tips at a constant tunneling current of 2.0 nA for a sample bias voltage with respect to the tip of 2.3 V. For the bare An surface, we observed an asymmetric peak at similar to2.01 eV, which is the typical STM-LE spectrum for the An sample-W tip system. For the C-60 monolayer-island, we observed a broad peak centered at similar to1.7 eV, which consists of the red-shifted emission from the underlying An substrate (similar to1.93 eV) and a new emission peak around 1.65 eV. The energy range of the new emission is consistent with that of the photoluminescence of the isolated Molecules and a 100 nm-thick film of C-60. Thus we conclude that the new emission peak is the fluorescence from the C-60 molecules in the monolayer-island. (C) 2002 Elsevier Science B.V. All rights reserved.