High-energy electrons and holes generated upon photoexcitation of plasmonic nanostructures are particularly attractive, as their excess energy can be potentially exploited to drive 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 this work, ultrafast transient absorbance measurements have been used to investigate the generation and relaxation of hot carriers following photoexcitation of bidimensional short-range-ordered arrays of gold nanoparticles. Different rise times of the transient signals generated for excitation at the plasmonic resonance or the interband transition have been measured.
To better understand the experimental findings, 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.
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: this process appears to "delay" the appearance of energetic electrons to that generated with plasmonic excitation.