Mid-infrared plasmons in scaled graphene nanostructures

TL;DR

This paper demonstrates mid-infrared plasmons in scaled graphene nanostructures, revealing damping mechanisms and substrate effects, and highlights potential applications in broad wavelength plasmonic devices.

Contribution

It provides the first detailed analysis of damping channels and substrate influences on mid-infrared graphene plasmons in nanostructures.

Findings

Graphene nanostructures as small as 50 nm support mid-infrared plasmons.

Damping channels include optical phonons and edge scattering.

Substrate choice significantly affects plasmon damping and dispersion.

Abstract

Plasmonics takes advantage of the collective response of electrons to electromagnetic waves, enabling dramatic scaling of optical devices beyond the diffraction limit. Here, we demonstrate the mid-infrared (4 to 15 microns) plasmons in deeply scaled graphene nanostructures down to 50 nm, more than 100 times smaller than the on-resonance light wavelength in free space. We reveal, for the first time, the crucial damping channels of graphene plasmons via its intrinsic optical phonons and scattering from the edges. A plasmon lifetime of 20 femto-seconds and smaller is observed, when damping through the emission of an optical phonon is allowed. Furthermore, the surface polar phonons in SiO2 substrate underneath the graphene nanostructures lead to a significantly modified plasmon dispersion and damping, in contrast to a non-polar diamond-like-carbon (DLC) substrate. Much reduced damping is realized when the plasmon resonance frequencies are close to the polar phonon frequencies. Our study paves the way for applications of graphene in plasmonic waveguides, modulators and detectors in an unprecedentedly broad wavelength range from sub-terahertz to mid-infrared.