Thermal Control of Material Placement in Heterostructured Metal Sulfide Nanorods

A hallmark of nanoparticle cation exchange reactions is their ability to deterministically place different materials at precise locations within the same nanoparticle. This synthetic control underpins a broad application space, with synergistic properties that emerge from the relative spatial arrangements of the materials. However, despite advances in our understanding of how and why certain arrangements of materials and interfaces are preferentially observed as products of cation exchange reactions, our knowledge of design guidelines and synthetic tuning knobs remains limited. Here, we correlate the placement of ZnS, CdS, Co₉S₈, and Cu_1.8S segments within heterostructured nanorods with the superionic transition temperature of copper sulfide, which is the most common nanoparticle template used for cation exchange. For cation exchange reactions that occur below the superionic transition temperature of approximately 100 °C, the resulting materials appear at various locations with the nanorods, including at the tips and within the body region. However, at higher cation exchange temperatures, material placement at the nanorod tips is observed almost exclusively. Additionally, we observe thin regions of copper sulfide sandwiched between Co₉S₈ and both ZnS and CdS, which help to relieve interfacial lattice strain. Overall, many different heterostructured nanorod architectures can be accessed through simple temperature-controlled partial cation exchange reactions that leverage interrelated contributions from interfacial lattice strain and the superionic nature of copper sulfide.