Effects of Copper Precursor Reactivity on the Shape and Phase of Copper Sulfide Nanocrystals

Controlling the crystal structure and shape and/or faceting of colloidal nanocrystals during growth through easily variable reaction parameters is highly desirable. The choice of precursors is one such parameter that can significantly impact achievable shapes and phases. Here, we examine how different Cu precursors in the synthesis of colloidal copper sulfide nanocrystals affect the resulting shape and crystal phase. An observed decreasing aspect ratio in one-dimensional nanorods (eventually transitioning to two-dimensional nanodisks) is consistent with the expected effects of decreasing Cu precursor reactivity. Nanorods are predominantly chalcocite at the early stages of growth, but a phase transition to djurleite occurs and is accompanied by a change in tip faceting upon further growth. In contrast, nanodisks appear in the djurleite phase early on and remain so upon continued growth. Localized surface plasmon resonance in various shapes of nanocrystals achieved is enhanced with chemical oxidation, and the near-field enhancement is also simulated.