Ultrafast Dynamics of Nonthermal Carriers Following Plasmonic and Interband Photoexcitation of 2D Arrays of Gold Nanoparticles

High-energy electrons and holes generated upon photoexcitation of plasmonic nanostructures are particularly attractive, as their excess energy can be potentially exploited for driving energetically demanding processes. The study of the ultrafast dynamics of these hot carriers is particularly relevant, as their successful harvesting is strongly affected by their short lifetimes. In particular, the dynamics of hot holes has not been completely explored, also due to the lack of direct measurements of their lifetimes. In this context, ultrafast transient absorbance measurements have been used to investigate the generation and relaxation of hot carriers in bidimensional short-range-ordered arrays of gold nanoparticles following photoexcitation either at the plasmonic resonance or at the interband transition, revealing different rise times of the transient signals generated along the two excitation pathways. These results are discussed in the light of the nature of the two types of excitations considering, in particular, the crucial role of the Auger-Meitner decay of the d-holes following the interband transition. To further understand these results, an empirical method to isolate the contribution of nonthermal electrons to the transient absorbance has been applied, showing that the appearance of the nonthermal electrons takes longer in the case of interband excitation than plasmonic excitation. This is consistent with a delayed appearance of energetic electrons due to the decay of the d-holes following the interband transition.