(83b) Efficient Hot Thermal Carrier Generation and Transfer in Plasmonic Metal Oxide Nanoparticles

Plasmonic materials are optically active materials with large extinction cross sections capable of producing energetic carriers that can perform chemical work in applications like solar cells and photocatalysts. Following plasmon excitation, the energetic carriers are either athermal, with chemical potential limited by absorbed photon energy, or thermalized carriers, with chemical potential limited by absorbed power. The most prominently studied plasmonic materials are coinage metals, which produce athermal carriers. Thus, hot carrier plasmonic devices have focused on the generation and harvesting of these athermal carriers. However, doped semiconductor plasmonic materials, like tin doped indium oxide (ITO), have recently emerged as infrared absorbing plasmonic materials. The mechanisms by which these materials generate hot carriers and if these can be harvested remains unclear. To date, there have been no observation of hot carrier harvesting in ITO or long-lived charge separation of a hot carrier in any semiconductor plasmonic-adsorbate pair.

In this study, we use transient absorption (TA) spectroscopy to show that the unique material properties of ITO enable efficient generation and transfer of thermalized energetic carriers from ITO to molecular adsorbate Rhodamine B (RhB). By analyzing electron transfer kinetics derived from TA, we observe hot electron transfer to RhB from ~0.6 to 1.8 ps with an external quantum efficiency of ~1%. We determine that charge transfer is independent of pump energy but strongly dependent on pump power consistent with thermalized carrier transfer rather than athermal carrier transfer. Results from the TTM and Marcus Theory show that efficient hot thermal electron generation in ITO results from its lower electronic heat capacity and shorter electron-electron scatter time. We conclude with new results highlighting how to engineer hot carrier generation and transfer in semiconductor plasmonic nanomaterials. These findings deepen our fundamental understanding of hot carrier generation and transport in semiconductor plasmonic materials, laying the groundwork for designing efficient, tunable plasmonic devices and enabling new high-irradiance energy harvesting applications.