Plasmonic properties of single gold nanosponges

Thanks to their mesoporous structure confined to a nanoscopic volume, the gold (Au) nanosponges ally the advantages of plasmonic nanoparticles together with those of nanoporous materials therefore offering insights into the plasmonic properties of their filaments. In this PhD thesis, the optical properties of Au nanosponges are revealed on the base of single particle measurements. In particular, a strong correlation between polarization-dependent scattering and the specific morphology of each Au nanosponge is observed whereas polarization-dependent photoluminescence is less influenced by the percolated structure of the Au nanosponges. First, white light scattering spectra are found to depend only weakly on the size and outer shape of each Au nanosponge, but are greatly influenced by their unique three-dimensional Au/air percolated structure. Polarization-dependent scattering reveals multiple spectrally overlapping plasmonic modes which originate from the Au filaments. Finite element calculations show that these multiple plasmon modes are responsible for numerous hotspots distributed inside each Au nanosponge. Furthermore, the polarization-dependent scattering and plasmon-assisted d-band photoluminescence of single Au nanosponges are compared. In contrast to small Au nanosponges, the polarization anisotropy of the scattering of large Au nanosponges is much stronger than the polarization anisotropy of their photoluminescence. Such disparity reflects the differences due to the methods of excitation. Indeed, a plane wave coherently excites all the hotspots (scattering) inside the Au nanosponge whereas a point-like dipole excites hotspots localized only within the limit of a plasmonic horizon (photoluminescence). This plasmonic horizon is determined by the lifetime of the plasmons and the velocity of the information that a plasmon has been created through the specific Au/air percolated structure of a nanosponge. Finally, preliminary experiments highlight that the hotspot distribution in the Au nanosponges can advantageously be used for the enhancement of linear and non-linear optical processes.submitted by Cynthia VidalZusammenfassung in deutscher SpracheUniversität Linz, Dissertation, 2017OeBB(VLID)191539