Cuprous oxide nanoshells with geometrically tunable optical properties.

We have systematically investigated the geometrically tunable optical properties of cuprous oxide (Cu(2)O) in a nanoshell geometry. Spherically symmetric Cu(2)O nanoshells with fine-controlled shell thicknesses and overall dimensions over a broad size range have been fabricated in a highly controllable manner through an Ostwald ripening-based symmetric hollowing process at room temperature. Symmetric hollowing of Cu(2)O particles can be achieved by using polyvinylpyrrolidone as a structural directing agent to mediate aggregation of the nuclei into solid spheres at the initial stage of the process, whereas when using other structural directing agents, such as polyethylene glycol, an asymmetric hollowing process takes place during Ostwald ripening, which gives rise to the formation of asymmetric Cu(2)O nanoshell structures. We demonstrate, both experimentally and theoretically, that the optical responses of Cu(2)O nanoshells can be fine-tuned in the visible spectral region by tailoring the inner and outer radii of the spherically symmetric nanoshells. Such optical tunability of Cu(2)O achieved in this nanoshell geometry is believed to be important to the optimization of Cu(2)O-based photonic materials and devices for photovoltaic and photocatalytic applications.