STM-induced photon emission from self-assembled porphyrin molecules on a Cu(100) surface

Abstract

An ultrahigh-vacuum scanning tunneling microscopy equipped with a conductive optical fiber tip and photon detector has been established to explore photon emission from a self-assembled monolayer (SAM) of Cu-tetra-[3,5-di-t-butylphenyl]porphyrin (Cu-TBPP) molecules on a Cu(100) surface. In a few nanometer scale areas, emitted photons from molecules induced by tunneling electrons were effectively collected within the near-field region through an apex of the conductive optical fiber tip. The photon emission can be attributed to the inelastic tunneling involving the optical fiber tip, the Cu-TBPP molecules, and the Cu(100) surface. We proposed two kinds of mechanisms in terms of the photon emission from a SAM of Cu-TBPP molecules on a Cu(100) surface. The quantum efficiency for molecular fluorescence induced by inelastic tunneling can be approximately estimated to be ∼3.0×10−6 photons per electron in the current experimental studies.