Precursor reaction kinetics control compositional grading and size of CdSe1−xSx nanocrystal heterostructures. Issue 26 (5th June 2019)

• Record Type: Journal Article
• Authors: Hamachi, Leslie S.; Yang, Haoran; Jen-La Plante, Ilan; Saenz, Natalie; Qian, Kevin; Campos, Michael P.; Cleveland, Gregory T.; Rreza, Iva; Oza, Aisha; Walravens, Willem; Chan, Emory M.; Hens, Zeger; Crowther, Andrew C.; Owen, Jonathan S.
• Is Part Of: Chemical science. Volume 10:Issue 26(2019)
• Page Start: 6539
• Page End: 6552
• Publication Date: 2019-06-05
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c9sc00989b
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : By varying precursor structure, core/shell and alloyed nanocrystal synthesis are performed in a single synthetic step. Abstract : We report a method to control the composition and microstructure of CdSe1− x S x nanocrystals by the simultaneous injection of sulfide and selenide precursors into a solution of cadmium oleate and oleic acid at 240 °C. Pairs of substituted thio- and selenoureas were selected from a library of compounds with conversion reaction reactivity exponents ( k E ) spanning 1.3 × 10 −5 s −1 to 2.0 × 10 −1 s −1 . Depending on the relative reactivity ( k Se / k S ), core/shell and alloyed architectures were obtained. Growth of a thick outer CdS shell using a syringe pump method provides gram quantities of brightly photoluminescent quantum dots (PLQY = 67 to 90%) in a single reaction vessel. Kinetics simulations predict that relative precursor reactivity ratios of less than 10 result in alloyed compositions, while larger reactivity differences lead to abrupt interfaces. CdSe1− x S x alloys ( k Se / k S = 2.4) display two longitudinal optical phonon modes with composition dependent frequencies characteristic of the alloy microstructure. When one precursor is more reactive than the other, its conversion reactivity and mole fraction control the number of nuclei, the final nanocrystal size at full conversion, and the elemental composition. The utility of controlled reactivity for adjusting alloy microstructure is discussed.