To date, there has been little control over the phase the results in nanocrystal synthesis, and synthetic achievements have been more serendipitous rather than deliberate. Our goal is to learn the synthetic principles needed to gain phase control in nanocrystal synthesis. Two recent research foci will be presented along this vein. Organosulfur precursors can be chosen carefully to tune the crystalline phases that results in synthesis if iron sulfides. There is a correlation between the sulfur content of the resultant phase with C-S bond strength of the organosulfur reagent. However, our evidence also shows that sometimes unique organic transformations that occur at the elevated temperature of the nanocrystal synthesis also influence phase. Diallyl disulfide, in particular, undergoes allylic rearrangements in oleylamine to produce persulfide units, directly synthesizing FeS2 pyrite. Cation exchange can be used to produce metastable wurtzite-type phases of the mixed copper sulfides, especially as CuInS2. Cation exchange is a known method for obtaining metastable phases as the anion sublattice retained in the reaction. While the wurtzite phase of CuInS2 can be formed from cation exchange of In3+ into hexagonal Cu2S, the opposite is not true. The result of cation cation exchange of Cu+ into hexagonal In2S3 results in a massive anion rearrangement and the formation of the thermodynamically favored chalcopyrite CuInS2.

Phase control in the synthesis of metal sulfide nanocrystals

255th National Meeting (2018)

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