Ultrafast Spatiotemporal Imaging of Disorder-Induced Strong Localization of Plasmon Resonances in Percolated Au Nanopillar Films.

A cyclic-sputtering technique is introduced for the self-assembled growth of nanopillars and the fabrication of percolated Au nanopillar films, which exhibit tunable quadrupolar resonances and a high percolating extinction in the near-infrared regime. More importantly, using photoemission electron microscopy (PEEM), several dark and luminous plasmonic eigenmodes enabled by disorder-induced resonance channels are identified. The percolating Au nanopillar films prepared with multiple deposition cycles (N = 84) demonstrate relative enhancements of 5.8, 36.8, and larger than 774.9 in percolating extinction, second-harmonic generation, and localized dark plasmon-assisted photoemission hotspots, respectively, compared with conventional percolating Au island films. Furthermore, it is revealed that the strong PEEM hotspots are induced by the interplay of dark and luminous modes, and the subsequent transport of excited nonthermal electrons is governed by quasi-ballistic electron scattering on the nanometer and femtosecond spatiotemporal scales. These findings advance the understanding of photonic Anderson localization and dynamical delocalization of dark plasmons in random nanostructures.