Lattice Strain and Ligand Effects on the Formation of Cu_2-xS/I-III-VI₂ Nanorod Heterostructures through Partial Cation Exchange

In the synthesis of anisotropic colloidal nanocrystal heterostructures, the interplay between many complicating factors such as interfacial chemistry, lattice strain, and coordinating ligands can make precise control over spatial distribution of composition extremely challenging. However, understanding how each complicating factor contributes to the growth mechanism can lead to otherwise difficult-to-achieve or unique structures and the means to tune their electronic/optical properties. Here, we report on the effects of lattice strain and the choice of ligands on the formation of Cu_2-xS/I-III-VI₂ colloidal nanorod heterostructures through partial cation exchange starting from Cu_2-xS nanorods. Lattice strain can induce alternating Cu_2-xS/CuGaS₂ segments along a colloidal nanorod if CuGaS₂ can nucleate easily from the sides of the nanorods. The choice in coordinating ligands can alter this preference to favor tip nucleation, in which case the resulting heterostructure has CuGaS₂/Cu_2-xS/CuGaS₂ rod/rod/rod geometry. In the less strained CuInS₂ case, superlattice-like alternating segmentation does not occur but the ligand induced difference in the preference of where nucleation initiates can still lead to distinct heterostructure morphologies. These results demonstrate how surface accessibility varied by the choice of ligands can be exploited synergistically with the driving force that creates interfaces to provide synthetic control over nanoscale heterostructure formation.