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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/221125
Enhanced Optical Response in Arrays of Multifunctional Plasmonic Nanostructures
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[eng] This thesis is devoted to the study of two plasmonic nanostructures that present a 3-fold symmetry, namely, inverted honeycomb lattices of bars and twisted stacks of triskelion nanostructures. These systems are particularly interesting due to the inherent geometric frustration originated by the mis- match between dipolar excitations, and the odd parity associated with the 3-fold symmetry. The combination of FDTD simulations with the fabrica- tion and subsequent far-field and near-field optical characterization of such structures allows for a multifaceted description of the system. In this thesis, a remarkable agreement between experiments and simulation is achieved, demonstrating the effectiveness of this combined approach in elucidating the response of plasmonic systems.
This thesis begins with a fundamental overview of the field, laying the groundwork for the essential concepts necessary for understanding the main findings presented in subsequent sections. These results are discussed in detail through the publications derived from this research. Furthermore, simulation methodologies, nanofabrication techniques, and characterization methods are introduced, as they form the core of the research presented herein.
Publications I and II are devoted to the study of inverted honeycomb plas- monic lattices. Here we prove the potential of such structures as refractive index sensors, taking advantage of the sharp SLR and the well-defined spec- tral dependence with the refractive index. The general sensing capabilities of this SLR can easily be expanded due to the out-of-plane electric field of hot spots spanning hundreds of nanometers away from the structure surface, providing a huge potential sensing volume. From a fundamental point of view, we have successfully characterized the plasmonic response of this system through state-of-the-art EELS experiments and FDTD simulations. By using EELS, both bright and dark modes can be detected. In particular, we present the first observation of resonances with an anti-ferroelectric arrangement of the dipolar excitations of the slits in the honeycomb lattice that occur with such spatial periodicity so that their unit cell has twice the
area of the honeycomb lattice. The samples presented in this part have been fabricated by EBL and specially dedicated FIB milling using Au ions to avoid contamination of the sample.
Publications III and IV focus on the study of two stacked triskelia nanostruc- tures, and their response as a function of the geometry of the structure, in particular, the twist angle between them. The triskelion motif is character- ized by its 3-fold symmetry and inherent two-dimensional chirality in 2D. This system holds two coupled plasmonic resonances tunable by control- ling the angle between both triskelia. We have demonstrated that a simple bonding-antibonding model is insufficient to fully elucidate the behavior of these two resonances. Instead, we have observed a continuous evolution of the excited modes as a function of the angle between the elements. Further insight into the combination of such resonances with SLR is proposed. The fabrication of this structure by successive EBL over large areas and high degree of alignment are also detailed.
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RODRÍGUEZ ÁLVAREZ, Javier. Enhanced Optical Response in Arrays of Multifunctional Plasmonic Nanostructures. [consulta: 28 de novembre de 2025]. [Disponible a: https://hdl.handle.net/2445/221125]