STM-induced molecular fluorescence from porphyrin molecules on metal substrates

Abstract

Molecular fluorescence from ultrathin layers of H2TBP porphyrin on Au(100) and ZnTBP porphyrin on Cu(100) has been generated by the electrical excitation using an ultrahigh-vacuum scanning tunneling microscope. The molecular origin of luminescence is justified by the good agreement of STM-induced emission spectra with conventional photoluminescence data excited from bulk molecules. The electronic states of top-layer molecules are effectively decoupled from the metal surface by controlling the thickness of molecular layers in a nanoscale regime. The porphyrin molecules are excited by the injection of hot electrons and then decay radioactively in a similar way to the photoluminescence process. These results provide a feasibility for the development of nanoscale molecular light source and spectroscopy.