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

• Published in: Nano letters 2013-12, Vol.13 (12), p.6210-6215
• Main Authors: Chen, Jianing, Nesterov, Maxim L, Nikitin, Alexey Yu, Thongrattanasiri, Sukosin, Alonso-González, Pablo, Slipchenko, Tetiana M, Speck, Florian, Ostler, Markus, Seyller, Thomas, Crassee, Iris, Koppens, Frank H. L, Martin-Moreno, Luis, García de Abajo, F. Javier, Kuzmenko, Alexey B, Hillenbrand, Rainer
• Format: Article
• Language: English
• Subjects: Carbon Compounds, Inorganic - chemistry; Collective excitations (including excitons, polarons, plasmons and other charge-density excitations); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Electromagnetic Fields; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; Graphene; Graphite - chemistry; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Materials science; Microscopy; Microscopy, Atomic Force; Monolayers; Nanostructure; Nanostructures - chemistry; Physics; Plasmons; Reflection; Silicon carbide; Silicon Compounds - chemistry; Specific materials; Surface and interface electron states; Surface Plasmon Resonance; Surface Properties; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties)
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl403622t

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 ultranarrow gaps. It also demonstrates that tip-enhanced near-field microscopy is a powerful contactless tool to examine nanoscale defects in graphene.