Light emission from organic molecules on metal substrates induced by tunneling currents

Tunneling currents in a scanning tunneling microscope were used to induce light emission by positioning either a gold-coated W tip on the surface of a porphyrin molecular monolayer on Cu(100) or a pure W tip on the surface of a perinone derivative monolayer on Au(100). The emission spectra from the surfaces of both molecules are dominated by the plasmon-mediated emission from substrates. Molecular fluorescence is completely quenched by the metal substrate. The organic molecules act as a spacer to modify the tip-induced plasmon modes, enhance the intensity of the plasmon-mediated emission, and cause blue shift of the spectra.