Molecular Orbital Gates for Plasmon Excitation.

Future combinations of plasmonicswith nanometer-sized electroniccircuits require strategies to control the electrical excitation ofplasmons at the length scale of individual molecules. A unique toolto study the electrical plasmon excitation with ultimate resolutionis scanning tunneling microscopy (STM). Inelastic tunnel processesgenerate plasmons in the tunnel gap that partially radiate into thefar field where they are detectable as photons. Here we employ STMto study individual tris-(phenylpyridine)-iridium complexes on a C60monolayer, and investigate the influence of their electronicstructure on the plasmon excitation between the Ag(111) substrateand an Ag-covered Au tip. We demonstrate that the highest occupiedmolecular orbital serves as a spatially and energetically confinednanogate for plasmon excitation. This opens the way for using moleculartunnel junctions as electrically controlled plasmon sources. [ABSTRACT FROM AUTHOR]