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Abstract
In this thesis, the plasmons of graphene nanoribbons are studied in detail using quantum mechanical tightbinding calculations combined with linear response in the random phase approximation. Plasmonics is a highly active research area that shows promise in a broad range of technological applications. One of the main interests stems from the ability of the plasmons to conﬁne light below the diffraction limit. Technological advances in nanofabrication–making structures on the nanoscale – and in the synthesis of twodimensional materials have enabled the fabrication of a vast range of experimental structures. To understand the plasmons at these tiny length scales, modeling of quantum mechanical effects has become increasingly important. For the two highsymmetry ribbon geometries – the armchair ribbon and the zigzag ribbon – the results presented are interpreted using insight from the Dirac model, which gives analytical expressions for the band structures. On the electronstructure level, comparisons between the Dirac model, the tightbinding method, and the even more detailed Density Functional Theory (DFT), are made, illustrating the value of analytical models for understanding numerical results. The plasmon calculations on narrow ribbons show strong dependence on the atomic conﬁguration at the ribbon edges, showing the importance of an atomistic modeling approach. Scale invariant plasmon energies are expected from the Dirac model, and are shown to emerge from the tightbinding calculations when the modeled ribbons are made wider and wider. Treating the higherorder plasmons as standing waves, a socalled FabryPérot model, we calculate nontrivial reﬂection phases and effective width corrections for the two ribbon types. Furthermore, we ﬁnd prominent shortrange oscillations of the induced charges of the plasmons. An effect that can be explained with our analysis of the wave functions.
Original language  English 

Place of Publication  Kgs. Lyngby 

Publisher  Technical University of Denmark 
Number of pages  118 
Publication status  Published  2018 
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Projects
 1 Finished

Theory of quantum plasmonics
Wedel, K. O., Wubs, M., Mortensen, N. A., Thygesen, K. S., Laurynenka, A., Kohler, S. & Pedersen, T. G.
15/04/2015 → 06/02/2019
Project: PhD