Abstract
Understanding and modeling of a surface-plasmon phenomenon on lossy metals interfaces based on simplified models of dielectric function lead to problems when confronted with reality. For a realistic description of lossy metals, such as gold and silver, in the optical range of the electromagnetic spectrum and in the adjacent spectral ranges it is necessary to account not only for ohmic losses but also for the radiative losses resulting from the frequency-dependent interband transitions. We give a detailed analysis of Surface Plasmon Polaritons (SPPs) and Localized Surface Plasmons (LPSs) supported by such realistic metal/dielectric interfaces based on the dispersion relations both for flat and spherical gold and silver interfaces in the extended frequency and nanoparticle size ranges. The study reveals the region of anomalous dispersion for a silver flat interface in the near UV spectral range and high-quality factors for larger nanoparticles. We show that the frequency-dependent interband transition accounted in the dielectric function in a way allowing reproducing well the experimentally measured indexes of refraction does exert the pronounced impact not only on the properties of SPP and LSP for gold interfaces but also, with the weaker but not negligible impact, on the corresponding silver interfaces in the optical ranges and the adjacent spectral ranges.
Highlights
Theoretical and experimental studies of surface plasmons and plasmon-active surfaces have revealed the great potential of plasmonics basing on the exploration of properties of metal-dielectric interfaces
Such anomalous behaviour known from optics is accompanied by a dramatic and intriguing modification to the phase velocity v = ω/ Re k of Surface Plasmon Polaritons (SPPs) of the surface longitudinal wave supported by the silver interface (Figure 7c, blue line, right column), the fact just mentioned in Reference [75]
Understanding and modeling of surface plasmon phenomena on lossy metals interfaces based on simplified models of dielectric function (DF) causes problems when confronted with reality
Summary
Theoretical and experimental studies of surface plasmons and plasmon-active surfaces have revealed the great potential of plasmonics basing on the exploration of properties of metal-dielectric interfaces. Not the electron behavior in a plasmonic nanostructure is of prime interest but the EM fields coupled to charge oscillations and confined to the metal-dielectric interface Such fields directly impact many processes that have found or are expected to be of potential in applications using propagating SPPs or those forming the standing waves of LSPs. Prediction for confined fields supported by the interface and their spatial distribution and dynamics are based on the self-consistent Maxwell’s electrodynamics in absence of the illuminating fields. The complex DF which reproduces well the measured real and imaginary parts of complex indexes of refraction of metals n(ω): εexp(ω) = n(ω)2 = (n (ω) + in (ω)) is a fundamental quantity which is directly related to the electronic structure of metals Such DF gives an insight into the elementary excitations of free carriers and interband absorption and allows us to study the basic surface plasmons characteristics supported by the interface. Understanding the role of ITs in such elementary geometries of interfaces is of basing importance in predicting the plasmonic performance of many metal nanostructures with the potential application ranging from photonics, chemistry, medicine, bioscience, energy harvesting, communication and information processing
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