Facet-dependent optical properties of Pd–Cu2O core–shell nanocubes and octahedra

Pd–Cu2O core–shell nanocubes and truncated octahedra with six average sizes for each particle shape have been synthesized from 29 nm Pd nanocubes. The nanocubes have average edge lengths of 64–124 nm, while the truncated octahedra are 107–183 nm in the opposite tip distance. The core and shell composition and lattice orientation have been determined, showing the formation of single-crystalline Cu2O shells. The surface plasmon resonance (SPR) band from the Pd nanocrystal cores is barely visible. However, the Cu2O shells display facet-dependent optical properties. The Cu2O absorption band for smaller Pd–Cu2O cubes is consistently more red-shifted than somewhat larger Pd–Cu2O truncated octahedra. This work again shows that the observed facet-dependent optical phenomenon in metal–Cu2O core–shell nanocrystals is derived from the Cu2O shells. The use of 40 nm Pd cubes as cores gave uniform and size-tunable Pd–Cu2O nanocubes and truncated octahedra that display the Pd SPR band. The Pd SPR band is consistently located at 650 nm for Pd–Cu2O truncated octahedra, and 670 nm for the cubes despite large variation in the shell thickness. Both the Cu2O absorption and the Pd plasmonic band exhibit facet-dependent optical properties.