Tip-plasmon mediated molecular electroluminescence on the highly oriented pyrolytic graphite substrate

Well-defined molecular fluorescence is realized by tunneling electron excitations from porphyrins on highly oriented pyrolytic graphite that is non-plasmonic in the visible spectral range. The occurrence of molecular electroluminescence is found to rely critically on the plasmonic emitting state of scanning tunneling microscope tip that is pre-examined on silver. These observations, together with the selective enhancement of molecular emission bands by energy-matching tip plasmons, suggest that the plasmonic field is indispensable for the generation of molecular electroluminescence, and the tip plasmon alone is sufficient in achieving this. Excitation of molecules directly by electrons is inefficient to produce light.