![]() Although these NRs had been previously synthesized by a colloidal seed-mediated method 41, 42, their plasmonic modes had not been identified so far as FRs. In this system, the spectrally localized LSPR modes of the Ag shell (the discrete levels) couple to the Au interband transitions (the continuum), showing remarkable tunability of the FRs. In this work, we report the observation of two different FRs on core–shell nanorods (NRs) composed of a Au core and a Ag shell NRs). However, these systems are easier to fabricate and are thus more attractive from the application point of view. In contrast, the generation of plasmonic FRs in highly symmetric metal nanoparticles is much more challenging indeed, only a few examples of them exist, such as bimetallic nanoparticles 25, 35, 36, metallic nanoshells 8, 21, and in some 37, 38, 39 an all-dielectric 40 core–shell nanostructures. The main disadvantage of this strategy is that the complex and/or asymmetric nanostructures are fabricated using intricate and expensive techniques 27, and/or only work under specific conditions 34, which largely reduce their applicability. Examples of this approach are non-concentric multilayered nanoshells 21, 22, 23, heterodimer nanostructures 6, 24, 25, ring-disk nanocavities 26, 27, 28, full nanocavities 29, nanoparticle clusters 7, 30, 31, 32, and nanocrystals supported on substrates 16, 33. Structural symmetry-breaking is the most common approach because it induces a non-uniform electromagnetic environment around the nanostructure, leading to the effective coupling between broad and narrow multipolar plasmon resonances. They have considerable potential for applications like waveguiding 11, 12, subwavelength optical imaging 13, 14, low-loss metamaterials preparation 12, 15, chemical and biological sensing 12, 16, 17, and energy harvesting 18, 19, to name a few.įRs are produced by the coupling of a discrete state with a continuum – e.g., between a narrow and a wide plasmon mode – and several plasmonic nanostructures have been proposed to display them 20. FRs are a type of resonant scattering phenomenon that gives rise to an asymmetric line-shape 9, 10. In particular, all-plasmonic Fano resonances (FRs) have attracted great interest during the past decade 6, 7, 8. ![]() Localized surface plasmon resonances (LSPRs) of metal nanoparticles, defined as collective oscillations of free electrons, have been extensively studied in recent years due to their versatility for a variety of applications, such as sensing, energy harvesting, and catalysis 1, 2, 3, 4, 5.
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