CdSe–CdSexTe1−x nanorod heterostructures: tuning alloy composition and spatially indirect recombination energies

In exploiting enhanced/new properties of the emerging class of heterostructured nanocrystals, challenges remain in the synthetic control over crystal size, composition and morphology. Parallel advances in characterization that provides atomic-level details of structure and composition along with their effects on materials' properties are necessary to be able to tailor nano-heterostructures for high-end applications. Here, we develop a synthetic strategy for forming type-II nanorod heterostructures with tunable band offsets by growing CdSexTe1−x alloys of variable composition on the tips of CdSe seeds. Composition in the nanorod heterostructures is quantified with atomic column resolution using aberration-corrected high-resolution STEM Z-contrast. The combination of Z-contrast analysis, high-resolution bright-field TEM imaging and photoluminescence studies reveals the energy of charge transfer transition across the heterointerface to be linearly dependent on both lattice constant and composition. The ability to vary the valence band offset, which is difficult to achieve by quantum size effect alone due to the effective mass of the hole often being large, is also demonstrated.