Facet-Dependent Optical Properties Revealed through Investigation of Polyhedral Au-Cu₂O and Bimetallic Core-Shell Nanocrystals.

The ability to prepare Au-Cu2O core-shell nanocrystals with precise control over particle size and shape has led to the discovery of facet-dependent optical properties in cuprous oxide crystals. The use of Au cores not only allows the successful formation of Au-Cu2O core-shell nanocrystals with tunable sizes, but also enables the observation of facet-dependent optical properties in these crystals through the Au localized surface plasmon resonance (LSPR) absorption band. By tuning the Cu2O shell morphology from rhombic dodecahedral to octahedral and cubic structures, and thus the exposed facets, the Au LSPR band position can be widely tuned. Such facet-dependent optical effects are not observed in bimetallic Au-Ag and Au-Pd core-shell nanocrystals with the same precisely tuned particle sizes and shapes. It is believed that similar facet-dependent optical properties could be observed in other ionic solids and other metal-metal oxide systems. The unusually large degree of plasmonic band tuning covering from the visible to the near-infrared region in this type of nanostructure should be quite useful for a range of plasmonic applications.