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.