Charge Separation on Localized Surface Plasmon and Hot Carrier Transfer to Semiconductors
Abstract: The relatively recent discovery that plasmonic nanoparticles generate energetic electron-hole pairs known as hot carriers has been the source of interest from many scientific groups. The capability to extract these short-lived hot carriers from metal nanoparticles (NPs) might potentially lead to applications in solar cells, photodetection, and photocatalysis. However, a better understanding of the hot carrier dynamics, starting from the formation process, is required. This thesis seeks to elucidate some aspects of charge formation, extraction, and hot carriers' recombination in plasmonic composite systems.First, two systems based on Ag and Au NPs were designed and studied to elucidate charge carriers' dynamics. The studies revealed that electrons and holes were effectively extracted and injected into suitable acceptors. Additionally, the electron injection and back transfer on TiO2 was significantly affected by the interface's status. The result motivated the following study that consisted of Au plasmonic NPs supported on different metal oxides, namely TiO2, ZnO, SnO2, and Al-ZnO (AZO). The electron dynamics on these systems were widely different. They could not be attributed solely to differences in the Schottky barrier height values, which suggested that interface status, electron bulk mobility, and oxide conduction band density of states are relevant factors to explain electron dynamics. The insertion of an insulator layer between the Au NPs and the metal oxides improved charge separation, which could be further explored to improve device efficiencies.In situ measurements on Au NPs/TiO2 samples were performed to investigate the effect of an increase of temperature in the range expected for device applications. This increase resulted in a higher number of electrons injected, which was attributed to the enhancement of plasmon decay by phonons.The last chapter investigates the change in the electron-phonon relaxation upon electron and hole injection, separately. Ab initio methods allowed theoretical investigation of this process and were used to predict the hole injection efficiency.
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