Strong Plasmon Reflection at Nanometer-Size Gaps in Monolayer Graphene on SiC

Abstract

We employ tip-enhanced infrared near-field microscopy to study the plasmonic properties of epitaxial quasi-free-standing monolayer graphene on silicon carbide. The near-field images reveal propagating graphene plasmons, as well as a strong plasmon reflection at gaps in the graphene layer, which appear at the steps between the SiC terraces. When the step height is around 1.5 nm, which is two orders of magnitude smaller than the plasmon wavelength, the reflection signal reaches 20% of its value at graphene edges, and it approaches 50% for step heights as small as 5 nm. This intriguing observation is corroborated by numerical simulations, and explained by the accumulation of a line charge at the graphene termination. The associated electromagnetic fields at the graphene termination decay within a few nanometers, thus preventing efficient plasmon transmission across nanoscale gaps. Our work suggests that plasmon propagation in graphene-based circuits can be tailored using extremely compact nanostructures, such as ultra-narrow gaps. It also demonstrates that tipenhanced near-field microscopy is a powerful contactless tool to examine nanoscale defects in graphene.

Anomalous reflection phase of graphene plasmons and its influence on resonators

“…Often, as is evident in these works, the analysis of the resonant absorption peaks has been based on the comparison with the dispersion relation of two-dimensional (2D) GPs via the relation k p = π/W , where W is the "active" part of the graphene ribbon (i.e., the region having a sufficiently high concentration of charge carriers). This simple relation between the modes inside the ribbon and 2D GPs corresponds to a Fabry-Pérot cavity with ideally reflecting walls and is justified by the high value of the GP reflection coefficient at a graphene edge [25,26]. Such an interpretation is, however, only valid when the phase shift of the GP reflected from the ribbon termination is −π .…”

“…virtually 100% amplitude [25,26]. This effect can be attributed to the large density of states on the GP channel (much larger than the density of photonic radiating modes).…”

Real-space mapping of tailored sheet and edge plasmons in graphene nanoresonators

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Plasmons in graphene nanoresonators have large application potential in photonics and optoelectronics, including room-temperature infrared and terahertz photodetectors, sensors, reflect-arrays or modulators [1][2][3][4][5][6][7] . Their efficient design will critically depend on the precise knowledge and control of the plasmonic modes.

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“…For that reason, graphene has a great potential for controlling radiation on the nanometer scale 18 , which largely benefits the development of highly sensitive spectroscopy 3 and detection [19][20][21] applications. The electromagnetic field concentration achieved by GPs can be further enhanced by fabricating nanostructures acting as Fabry-Perot resonators for GPs (for example disks or ribbons) 1,2, 6, 7,22 , favoring strong absorption in arrays of the resonators (up to 40%) 7 . Until now, localized plasmonic modes in graphene ribbons and disks have been analyzed experimentally essentially by far-field spectroscopy 1,2, 6, 7,22 .…”

Graphene Sandwiches as a Platform for Broadband Molecular Spectroscopy

“…[26][27][28] The most impressive of which is probably the extreme compression of these surface waves with lateral confinement extending only a few nanometres away from the graphene sheet. [29][30][31][32][33] Furthermore, the transparency of graphene gives rise to particular hybridized modes in coupled sheets. 34 This is even more striking in paired ribbons where the contribution from the edges can result in unexpected field profiles.…”