Light Emission and Conductance Fluctuations in Electrically Driven and Plasmonically Enhanced Molecular Junctions

TL;DR

This study investigates how atomic-scale fluctuations affect light emission and conductance in plasmonically enhanced molecular junctions, revealing microscopic variability yet long-term device stability.

Contribution

It demonstrates correlated conductance and emission fluctuations in nanoparticle-bridged molecular junctions at room temperature, highlighting atomic-scale effects in nanoscale optoelectronic devices.

Findings

Conductance and light emission are highly sensitive to atomic fluctuations.

Discrete conductance steps correlate with emission intensity changes.

Devices maintain functionality over months despite microscopic fluctuations.

Abstract

Electrically connected and plasmonically enhanced molecular junctions combine the optical functionalities of high field confinement and enhancement (cavity function), and of high radiative efficiency (antenna function) with the electrical functionalities of molecular transport. Such combined optical and electrical probes have proven useful for the fundamental understanding of metal-molecule contacts and contribute to the development of nanoscale optoelectronic devices including ultrafast electronics and nanosensors. Here, we employ a self-assembled metal-molecule-metal junction with a nanoparticle bridge to investigate correlated fluctuations in conductance and tunneling-induced light emission at room temperature. Despite the presence of hundreds of molecules in the junction, the electrical conductance and light emission are both highly sensitive to atomic-scale fluctuations -- a phenomenology reminiscent of picocavities observed in Raman scattering and of luminescence blinking from photo-excited plasmonic junctions. Discrete steps in conductance associated with fluctuating emission intensities through the multiple plasmonic modes of the junction are consistent with a finite number of randomly localized, point-like sources dominating the optoelectronic response. Contrasting with these microscopic fluctuations, the overall plasmonic and electronic functionalities of our devices feature long-term survival at room temperature and under an electrical bias of a few volts, allowing for measurements over several months.