Nanoelectromechanical modulation of a strongly-coupled plasmonic dimer

Jung-Hwan Song,Qitong Li,Ju-Hyung Kang,Pieter G Kik,Søren Raza,Jorik Van De Groep,Mark L Brongersma

doi:10.1038/s41467-020-20273-2

Abstract

The ability of two nearly-touching plasmonic nanoparticles to squeeze light into a nanometer gap has provided a myriad of fundamental insights into light–matter interaction. In this work, we construct a nanoelectromechanical system (NEMS) that capitalizes on the unique, singular behavior that arises at sub-nanometer particle-spacings to create an electro-optical modulator. Using in situ electron energy loss spectroscopy in a transmission electron microscope, we map the spectral and spatial changes in the plasmonic modes as they hybridize and evolve from a weak to a strong coupling regime. In the strongly-coupled regime, we observe a very large mechanical tunability (~250 meV/nm) of the bonding-dipole plasmon resonance of the dimer at ~1 nm gap spacing, right before detrimental quantum effects set in. We leverage our findings to realize a prototype NEMS light-intensity modulator operating at ~10 MHz and with a power consumption of only 4 fJ/bit.

Highlights

The ability of two nearly-touching plasmonic nanoparticles to squeeze light into a nanometer gap has provided a myriad of fundamental insights into light–matter interaction
The energy loss spectroscopy (EELS) simulations are performed with the Metallic NanoParticles Boundary Element Method (MNPBEM) toolbox for MATLAB, which solves Maxwell’s equations in the presence of an electron beam
The bonding dipole (BDP) mode continues to red-shift, at astounding rates over 100 meV for each nanometer of movement. Based on their different modal symmetries, the BDP and anti-bonding dipole (ADP) are most effectively excited and probed in different spatial locations. This can be seen in the simulated EELS maps for these modes of a fabricated dimer (Fig. 1e) in the strong coupling regime

Summary

Introduction

The ability of two nearly-touching plasmonic nanoparticles to squeeze light into a nanometer gap has provided a myriad of fundamental insights into light–matter interaction. The extreme light confinement renders the dimer’s optical response very sensitive to minute changes in gap size[8] and facilitates the observation of a variety of intriguing quantum effects[9,10,11,12,13] These findings naturally prompt the fundamental questions to what extent fields can be concentrated and resonances be tuned[14]. We design and implement a nano-electromechanical system (NEMS) to dynamically modulate the gap of a dimer at the ultimate, atomic scale (~1 nm), which allows operation at fundamentally-limited optical sensitivities and achievement of low-power (~1 fJ/bit), high-speed (~10 MHz) manipulation of optical signals. We dynamically follow the modal hybridization of a single, dimer element upon electromechanical actuation inside a transmission electron microscope (TEM)

Objectives

Methods

Results

Conclusion