Gold Nanorod Plasmon Resonance Damping Effects on a Nanopatterned Substrate

Substrate properties might significantly influence the scattering spectra of supported plasmonic nano-particles because of different damping mechanisms. In this work, indium tin oxide substrates are modified by the combination of nanosphere lithography and ion-bombardment to create a nanopattern with sharp boundaries between the irradiated and masked regions. The single-particle scattering spectra of gold nanorods distributed over the nanopattern are investigated in detail. For nanorods located purely on either the masked or implanted areas, the spectra can be adequately interpreted in terms of a classical damped harmonic oscillator model, taking the chemical interface damping into account. When the particles overlap the masked and irradiated areas, however, markedly a different behavior is found depending on the actual arrangement. For the rods experiencing a symmetric inhomogeneity (i.e., by bridging between two masked regions), damping varies smoothly with the extent of substrate inhomogeneity. For the asymmetric case (rods overlapping the boundary between the implanted and masked zones), a sudden increase of the damping is found, which is rather independent on the specific extent of substrate inhomogeneity. Comparing the damping variations with the related intensity changes indicates that substrate inhomogeneity at such length scales results in a different behavior than predicted by the classical damped harmonic oscillator model applied for nanoparticles encapsulated or homogeneously surrounded by molecular coatings.