Due to their unique optical properties plasmonic metal/semiconductor nano-heterostructures (MSNH) are promising materials for applications ranging from imaging and photonics to solar energy conversion and photocatalysis. In recent years, several charge transfer and resonant energy transfer mechanisms have been proposed for plasmons in MSNHs, however, the very first steps of plasmon decay and coupling have not been directly observed yet due to their short lifetime of tens of femtoseconds. However, direct measurements of plasmon decay and plasmon/exciton coupling are of crucial importance for advancements in science and technology alike. The new approach that is presented here combines model systems consisting of ordered nanoparticle arrays with exceptional homogeneity that enable systematic variations in materials properties and that are compatible with ultrafast chirp-free transient absorption measurements with time resolution below 20 fs. Comparison of plasmon dynamics and hot charge carrier dynamics in Au/Cu2O core-shell nanoparticle arrays show that the majority of hot charge carriers is transferred to the semiconductor following Landau damping in the metal on a 40 fs time scale. Measurements of Au/Ag alloy nanoparticles with and without semiconductor shells revealed the composition dependents of plasmon dynamics. These measurements lay the groundwork for directly studying plasmon-exciton coupling mechanisms in real-time.

Ultrafast plasmon dynamics in hybrid metal/semiconductor nanostructures

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