Plasmon delocalization onset in finite sized nanostructures

Abstract

Abstract: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 nearfield 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. nanoshells for combined optical imaging and photothermal cancer therapy," Nano Lett. 7(7), 1929-1934 (2007). 10. J. Homola, S. S. Yee, and G. Gauglitz, "Surface plasmon resonance sensors: review," Sens. Actuators B Chem. ©2011 Optical Society of America54(1-2), 3-15 (1999). 11. D. K. Gramotnev, and S. I. Bozhevolnyi, "Plasmonics beyond the diffraction limit," Nat. Photonics 4(2), 83-91 (2010). 12. P. Berini, "Plasmon polariton modes guided by a metal film of finite width," Opt. Lett. 24(15), 1011-1013 (1999). 13. P. Berini, R. Charbonneau, and N. Lahoud, "Long-range surface plasmons on ultrathin membranes," Nano Lett. 4370-4379 (1972). 23. W. Lukosz, and M. Meier, "Lifetimes and radiation patterns of luminescent centers close to a thin metal film,"Opt. Lett. 6(5), 251-253 (1981 874-881 (1957). 26. D. Sarid, "Long-range surface-plasma waves on very thin metal films," Phys.

Coupling of multiple LSP and SPP resonances: interactions between an elongated nanoparticle and a thin metallic film

“…At these sizes, the LSP modes are standing wave plasmons at specific frequencies and k x values, which together form peaks along the dispersion curve of the even SPP mode [24]. Thus, one should see a similar coupling interaction as that in Fig.…”

“…1(c)]. Note, the central branch corresponding to mode II is of greatest intensity, since it exhibits a close to symmetric E x field component along the top and bottom interfaces of the particle, much like that exhibited by the many localized modes of the single elongated Ag particle in freespace [24]. The branch corresponding to mode III is of smallest intensity, since the field is most concentrated along the glass-Ag interface and thus, is excited least efficiently.…”

“…Notice that coupling between the many localized modes of the particle and the SPP continuum of the film occurs only for mode II. This is simply due to the fact that in this case, SPPs are bound to both interfaces of the top Ag film, and that they exhibit a close to symmetric E x field profile in the top Ag film, just like that exhibited by the many localized modes of the single elongated Ag particle in freespace [24]. Note, however, that we do not expect the field E x to be completely symmetric in the top film, since the total environment itself is not symmetric.…”

“…These modes are essentially standing wave surface plasmons and together form the continuum of the even SPP mode as L → ∞ [24]. This assumption still holds for this particle-film system, since the particle is spaced 100 nm from the surface of the film.…”

“…1(a), a horizontally oriented electric dipole source placed 100 nm to the left of the particle is used for excitation. A study of the system response for a finite length L is made via the same Fourier analysis method as in a previous work [24]. The plots obtained display the magnitude of the parallel k-vector component k x at each given frequency.…”