Photon emission induced by tunneling electrons from a Cu(100) surface covered with porphyrin molecules

An ultrahigh-vacuum scanning tunneling microscope with an optically transpa rent tip was used to excite photon emission from a clean Cu(1 0 0) surface and a sub-monolayer of Cu-tetra-[3,5-di-t-butylphenyl]porphyrin (Cu-TBPP) m olecules chemisorbed on a Cu(1 0 0) surface. Photons generated in a nanomet er-scale area just under the tip were collected within the near-field regio n through the apex of the optical fiber tip. Two kinds of mechanisms for th e photon emission from a Cu-TBPP/Cu(1 0 0) surface are proposed. The quantu m efficiency for molecular fluorescence induced by inelastic tunneling was estimated to be similar to3 x 10(-6) photons/electron. (C) 2001 Elsevier Sc ience B.V. All rights reserved.