Contrast between Surface
Plasmon Polariton-Mediated
Extraordinary Optical Transmission Behavior in Epitaxial and Polycrystalline
Ag Films in the Mid- and Far-Infrared Regimes
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Abstract
In this Letter we report a comparative study, in the
infrared regime,
of surface plasmon polariton (SPP) propagation in epitaxially grown
Ag films and in polycrystalline Ag films, all grown on Si substrates.
Plasmonic resonance features are analyzed using extraordinary optical
transmission (EOT) measurements, and SPP band structures for the two
dielectric/metal interfaces are investigated for both types of film.
At the Si/Ag interface, EOT spectra show almost identical features
for epitaxial and polycrystalline Ag films and are characterized by
sharp Fano resonances. On the contrary, at the air/Ag interface, dramatic
differences are observed: while the epitaxial film continues to exhibit
sharp Fano resonances, the polycrystalline film shows only broad spectral
features and much lower transmission intensities. In corroboration
with theoretical simulations, we find that surface roughness plays
a critical role in SPP propagation for this wavelength range