Oleic acid assisted formation mechanism of CuInS2 nanocrystals with tunable structures

Abstract

Distinct from the popular opinion that only the zinc-blende CuInS₂ phase could be prepared in the presence of oleic acid (OA), CuInS₂ nanocrystals with different phase structures and shapes were synthesized by a facile heat-up method through simply adjusting the OA dosage. Zinc-blende CuInS₂ quantum dots (QDs) with a triangular pyramidal shape were obtained at a low dosage of OA (<1 mL). With an increase in the OA dosage (∼1.5 mL), wurtzite CuInS₂ hexagonal nanoplates were formed accompanied by zinc-blende CuInS₂ QDs. A higher OA dosage (2–3 mL) led to the production of wurtzite CuInS₂ hexagonal nanoplates. The formation of the CuInS₂ nanocrystals with tunable structures was mainly attributed to the role of OA dosage in the formation and transformation of a CuIn(SR)_x intermediate. A high OA dosage could facilitate the formation and crystallization of the intermediate, giving a metastable wurtzite CuInS₂ structure that could be gradually converted into a stable zinc-blende CuInS₂ QDs as the reaction proceeded. However, a low OA dosage would lead to low crystallinity of the intermediate, and thus the intermediate was transformed into a stable zinc-blende CuInS₂ phase easily. Therefore, our work could provide guidance for the controllable synthesis of other multi-component chalcogenide nanocrystals.