Plasmon Resonances and Structures of Chalcogenide Alloy Nanocrystals

Alloying on the nanoscale is a powerful chemical handle for tuning the structural, electronic, and optical properties through continuous composition variation. Here, we explore the impact of alloying on the structural and optoelectronic properties of copper chalcogenide nanocrystals. Cuprous selenide-sulfide alloy nanocrystals were made by the cation exchange reaction. The nanocrystals upon oxidation exhibit localized surface plasmon resonances. The localized surface plasmon resonance frequency follows an anomalous trend as a function of the alloy composition. Similar behavior is seen for the electrical properties of the alloy nanocrystals with markedly suppressed conductivities measured at the intermediate compositions. This anomalous behavior originates from the mixed-phase nature of individual nanocrystals at the intermediate compositions and structural disorder resulting from the drastic difference in anionic sublattice structures of cuprous selenide and cuprous sulfide phases. This study shows that alloy nanocrystals produced by the cation exchange reaction can have complex intraparticle structures and properties.