Investigating Plasmonic Resonances in Metal/Semiconductor Heterostructures

Metal/semiconductor heterostructures have shown promise in the field of plasmonics, with possible applications towards solar energy conversion, opto-electronics, and photocatalysis. In particular, plasmon-induced transfer of carriers from the metal to semiconductor components of the system is not yet well understood, let alone the material properties that would most enhance this plasmon-induced transfer. Therefore, ultrafast spectroscopic measurements on various heterostructures with tuned properties are required. The chosen systems of study are two-dimensional Au/Cu2O hemispherical nano-heterostructure arrays. By varying the semi-shell thickness, we can tune the plasmonic resonance, and ultimately the plasmonic coupling and the corresponding charge transfer processes. Charge transfer mechanisms of these systems are studied with transient absorption spectroscopy (TAS) and time-domain terahertz spectroscopy (TDTS). Hot hole dynamics are extracted from the TAS measurements, while TDTS further investigates the plasmonic properties. Results show that wavelength-dependent hot hole transfer that occurs after the localized surface plasmon undergoes Landau damping, and that terahertz emission from these nano-heterostructure arrays are dependent on the metal atom used for the core as well as the core-shell size. This study could be expanded to a broader range of metal-semiconductor hybrids, where the fine-tuning of their properties can lead to the design of optimized plasmonic materials.