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Substrate-based tuning of plasmon resonances on gold nanoparticles (NP) is a versatile method of achieving plasmon
resonances at a desired wavelength, and offers reliable nanogap sizes and large field enhancement factors. The
reproducibility and relative simplicity of these structures makes them promising candidates for frequency-optimized
sensing substrates. The underlying principle in resonance tuning of such a structure is the coupling between a metal
nanoparticle and the substrate, which leads to a resonance shift and a polarization dependent scattering response. In this
work, we experimentally investigate the optical scattering spectra of isolated 60 nm diameter gold nanoparticles on
aluminum oxide (Al2O3) coated gold films with various oxide thicknesses. Dark-field scattering images and scattering
spectra of gold particles reveal two distinct resonance modes. The experimental results are compared with numerical
simulations, revealing the magnitude and phase relationships between the effective dipoles of the gold particle and the
gold substrate. The numerical approach is described in detail, and enables the prediction of the resonance responses of a
particle-on-film structure using methods that are available in many available electromagnetics simulation packages. The
simulated scattering spectra match the experimentally observed data remarkably well, demonstrating the usefulness of
the presented approach to researchers in the field.
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