Wide-Band Nano-Imaging of Plasmon Dispersion and Hotspots in Quasi-Free-Standing Epitaxial Graphene

TL;DR

This study uses wide-band nano-imaging with s-SNOM and tunable lasers to measure graphene plasmon dispersion over a broad spectrum, revealing hotspots and enabling precise electrical property measurement and control of plasmon reflection.

Contribution

It introduces a wide-band nano-imaging technique with tunable lasers to measure graphene plasmon dispersion and hotspots, advancing spatial control and electrical characterization.

Findings

Measured plasmon dispersion from 140 to 1700 nm wavelength.

Extracted electron Fermi energy of 298±4 meV.

Demonstrated wavelength-tuneable plasmon reflection hotspots.

Abstract

We report observation of graphene plasmon interference fringes across a wide spectral range using a scattering scanning near-field optical microscope (s-SNOM) that employs a widely tunable bank of quantum cascade lasers. We use plasmon interference to measure the dispersion curve of graphene plasmons over more than an order of magnitude of plasmon wavelength, from $\lambda_{sp}$ ~140 to ~1700 nm, and extract the electron Fermi energy of 298$\pm$4 meV for hydrogen-intercalated single layer epitaxial graphene on SiC. Furthermore, we demonstrate the appearance of wavelength tuneable graphene plasmon reflection "hotspots" at single-layer/bi-layer interfaces. This work demonstrates the capability of wide-band nano-imaging to precisely measure the electrical properties of graphene and spatially control plasmon reflection focusing.