Atomic Fluctuations and Light Emission in Electrically Excited Plasmonic Nanojunction

Plasmonic nanostructures with electrical leads can efficiently couple electrical and optical degrees of freedom in a nanoscale device. Unlike conventional plasmonic systems, resonance modes of such nanojunctions can be electrically excited by inelastic tunneling of electrons [1]. Interestingly, nontraditional light emission processes can also be observed in these junctions with photon energies significantly higher than the energy of the incident electrons. They were demonstrated in STM-based and electromigrated junctions and are attributed to hot carriers [2] or co-herent multielectron scattering processes [3]. However, these structures lack stability and reproducibility. In this work, we demonstrate nanoparticle based tunnel junction with molecular spacer that shows overbias emission in addition to the plasmon enhanced inelastic tunneling emission. The spectra and image of the light emission are shown in Fig 1a and 1b respectively. Benefitting from the outstanding long-term stability of the device, the same nanoparticle junction can be studied over weeks. Furthermore, we investigate the impact of atomic fluctuations in the junction on both its photoemission and electrical transport characteristics. Random fluctuations in gold atom-molecule contact within the same junction is evidenced as telegraph noise in the conductance associated with fluctuating contributions of different plasmonic modes to the electroluminescence, as observed for photo-excited metal luminescence in similar junctions [4]. Besides enabling the investigation of atomic-scale dynamics in metal-molecule contacts, our system contributes to the development of nanoscale light sources and ultrafast optoelectronics.