Transformation from Cu_2–xS Nanodisks to Cu_2–xS@CuInS₂ Heteronanodisks via Cation Exchange

Cationic-exchange methods allow for the fabrication of metastable phases or shapes, which are impossible to obtain with conventional synthetic colloidal methods. Here, we present the systematic fabrication of heteronanostructured (HNS) Cu_2–xS@CuInS₂ nanodisks via a cationic-exchange reaction between Cu and In atoms. The indium–trioctylphosphine complex favorably attacks the lateral (16 0 0) plane of the roxbyite Cu_2–xS hexagon. We explain the phenomena by estimating the formation energy of vacancies and the heat of reaction required to exchange three Cu atoms with an In atom via density functional theory calculations. In an experiment, a decrease in the amount of trioctylphosphine surfactant slows the reaction rate and allows for the formation of a lateral heterojunction structure of nanoplatelets. We analyze the exact structures of these materials using scanning transmission electron microscopy–energy dispersive X-ray spectroscopy and high-resolution transmission electron microscopy. Moreover, we demonstrate that our heteronanodisk can be an intermediate for different HNS materials; for example, adding gold precursors to a Cu_2–xS@CuInS₂ nanodisk results in a AuS@CuInS₂ nanodisk via an additional cationic reaction between Cu ions and Au ions.