Plasmonic metal/semiconductor nano-heterostructures (MSNH) such as Au/Cu₂O can route, manipulate, and concentrate light at a nanometer length scale. Recently, it was observed that they can also be employed to convert the energy contained in plasmonic excitations into other forms of excitations such as hot charge carriers and excitons. These unique properties have prompted their investigation for various potential applications such as solar energy conversion, biotherapy, photocatalysis, photodetection, and photovoltaics. However, the mechanism involved in the conversion of plasmonic excitations into other forms of excitation in a MSNH has not been fully understood. This knowledge is critical for novel plasmonic innovations in science and technology. Here, we combine a flexible strategy for fabricating a highly ordered, homogeneous array of Au/Cu₂O with a well-resolved, chirp-compensated ultrafast measurement to investigate the dynamics of hot charge carriers within the domains of the heterostructure. The regular arrays of Au/Cu₂O are fabricated by combining a nanosphere lithography technique with a chemical bath deposition process. Ultrafast measurements are performed by employing highly resolved, chirp-compensated transient absorption spectroscopy (TAS) with an exceptional time resolution of sub 30 fs. Further measurements are performed on the nanoparticles following surface modifications and alloying with Ag nanoparticles. Results obtained from steady-state absorption measurements are employed to select two photoexcitation wavelengths. These include wavelengths to exclusively excite Au without exciting Cu₂O (below Cu₂O bandgap excitation) and to excite both Au and Cu₂O domains (above Cu₂O bandgap excitation). In addition, results obtained from TAS measurement on pure Au, Cu₂O, and Au/Cu₂O display exciting features that could give credence to a model that describes the transfer of hot charge carriers within the domains

Abhinav Prabhakar

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