Tailoring Cation Exchange in Nanomaterials

Abstract

In this thesis, metal exchange in two different nanocrystalline systems is explored. Firstly, the partial In3+ for Cu+ cation exchange in a colloidal nanocrystal system of copper sulfide is studied. Excess trioctylphosphine is determined to be an effective addition to the cation exchange reaction that stabilizes the resulting wurtzite copper indium sulfide nanocrystals and allows for samples synthesized with less than stoichiometric In/Cu precursor ratios to be luminescent. Additionally, gallium incorporation into these CuInS2 nanocrystals is shown to improve and blue shift the luminescence. Secondly, cadmium for indium exchange is studied in a solid system of InSb nanowires. This reaction is unexpected due to the covalent character of the initial material. However, the reaction is discovered to undergo complete transformation from InSb to Cd3Sb2 upon reaction of a nanowire wafer with a cadmium oleate solution containing an excess of oleic acid. This complete transformation does not occur with other metal oleates, such as, copper, zinc and bismuth, in the same manner, or at all. Cation exchange is observed, and the progress monitored in colloidal nanocrystal systems and solid templates. Studying these cation exchanges helps us to understand the mechanisms of the reactions and predict the outcomes of similar exchange systems.