When do plasmons start to propagate?
© 2014 EPFL
The transition from localized to delocalized plasmons (i.e. the transition from a situation where the decay length of a travelling surface plasma wave is greater than its propagation distance to a situation where it is smaller) and hence the onset of plasmon delocalization is studied in a single 2D silver nanoparticle of increasing length. A fourier analysis in the near-field of the nanoparticle is used as the main tool for analysis. This method, along with far-field scattering spectra simulations and the near-field profile directly above and along the length of the nanoparticle are used to investigate and clearly show the transition from localized to delocalized modes. In particular, it is found that for a finite sized rectangular nanoparticle, both the emerging odd and even delocalized modes are nothing but a superposition of many standing wave plasmon modes. As a consequence, even very short metal films can support delocalized plasmons that bounce back and forth along the film.
There exist two types of plasmon resonant modes: those that are localized around particles and those that can propagate on a metallic film. Recently, we addressed the very fundamental question of the transition from localized to delocalized plasmons (i.e. the transition from a situation where the decay length of a travelling surface plasma wave is greater than its propagation distance to a situation where it is smaller) and hence the onset of plasmon delocalization was studied in a single 2D silver nanoparticle of increasing length. A fourier analysis in the near-field of the nanoparticle was used as the main tool for analysis. This method, along with far-field scattering spectra simulations and the near-field profile directly above and along the length of the nanoparticle were used to investigate and clearly show the transition from localized to delocalized modes.
The following figure shows the dispersion relations for plasmons propagating along finite silver strips with different lengths (2.5 μm on the left and 5 μm on the right). A remarkable finding of this study is that even very short metal films can support delocalized plasmons that bounce back and forth along the film.
Check the corresponding publication: PDF External link: doi: 10.1364/OE.19.011387