Longitudinal Strain Engineering of Cu_{2- x}S by the Juxtaposed Cu₅FeS₄ Phase in the Cu₅FeS₄/Cu_{2- x}S/Cu₅FeS₄ Nanosandwich

Structurally well-defined heteronanoparticles have received great attention because their distinct structural features can be altered to achieve unprecedented properties. The cation exchange reaction, one of the most powerful techniques to synthesize heteronanoparticles, can tune the regiospecific composition of nanoparticles while maintaining the overall morphology of the template. Herein, we demonstrate that the nascent interface between the cation-exchanged region and the unchanged template can induce a significant tensile or compressive strain on the lattice of the template so that the cation exchange process at the interface can be greatly facilitated. The fate of the overall cation exchange reaction can be dictated by placing the initial cation exchange sites on the template regioselectively. Via a careful kinetic and thermodynamic control of the cation exchange, we could prepare two completely different nanostructures of Cu₅FeS₄/Cu_2-xS/Cu₅FeS₄ nanosandwich and Cu₅FeS₄/Cu_2-xS Janus nanoparticle. The synthetic concept described in this study could be further extended to the synthesis of various rationally designed multiphasic nanoparticles with exciting physicochemical properties.