STM induced photon emission from adsorbed porphyrin molecules on a Cu( 100) surface in ultrahigh vacuum D. Fujita, T. Ohgi, W.-L. Deng, H. Nejo, T. Okamoto, S. Yokoyama, K. Kamikado, S. Mashiko Abstract Photon emission induced by tunneling electrons has been observed from a submonolayer of Cu-tetra- [3,5-di-t-butylpheny1] porphyrin (Cu-TBPP) molecules chemisorbed on a Cu(100) surface in ultrahigh vacuum. Near-field photons generated in a nanometer-scale region with Cu-TBPP molecules were collected effectively through the apex of a conductive optical fiber tip. The photon emission mechanism can be attributed to the inelastic tunneling events involving the tip, the Cu-TBPP molecules, and the Cu( 100) substrate.