Influence of the Nanoscale Kirkendall Effect on the Morphology of Copper Indium Disulfide Nanoplatelets Synthesized by Ion Exchange

CuInS2 nanocrystals are prepared by ion exchange with template Cu2-xS nanoplatelets and InX3 [X = chloride, iodide, acetate (0Ac), or acetylacetonate (acac)]. The morphologies of the resultant nanocrystals depend on the InX3 precursor and the reaction temperature. Exchange with InCl3 at 150 degrees C produces CuInS2 nanoplatelets having central holes and thickness variations, whereas the exchange at 200 degrees C produces intact CuInS2 nanoplatelets in which the initial morphology is preserved. Exchange with InI3 at 150 degrees C produces CuInS2 nanoplatelets in which the central hollowing is more extreme, whereas exchange with In(0Ac)(3) or In(acac)(3) at 150 degrees C produces intact CuInS2 nanoplatelets. The results establish that the ion exchange occurs through the thin nanoplatelet edge facets. The hollowing and hole formation are due to a nanoscale Kirkendall Effect operating in the reaction-limited regime for displacement of X- at the edges, to allow insertion of In3+ into the template nanoplatelets.