Nanoscale Electrical Excitation of Surface Plasmon Polaritons with a Nanoantenna Tunneling Junction

Quantum tunneling-driven optical nanoantennas are keycomponentsfor the development of integrated plasmonic nanodevices. In this work,we use the tunneling junction between a nanoantenna and a thin goldfilm to electrically excite propagating surface plasmons on the nanoscale.The nanoantenna is a chemically synthesized gold nanocube (& SIM;50nm side length) that is separated from a thin (50 nm) gold film byan insulating molecular layer (1,8-octanedithiols, & SIM;1 nm thick).A novel method for completing the electrical circuit between the nanoantennaand the gold film using an atomic force microscope (AFM) is developed.Based on the results of numerical modeling, the nanoantenna modesexciting the propagating surface plasmon polaritons are identifiedas hybridized gap and antenna modes. Our results demonstrate the abilityto interrogate individual tunneling-driven nanoantennas, a crucialstep toward the development of electrical nanosources of surface plasmonpolaritons and light.