Structural evolution in metal oxide/semiconductor colloidal nanocrystal heterostructures

Colloidal nanocrystal heterostructures in which two or more chemically distinct inorganic components are epitaxially fused together provide new opportunities in developing multifunctional building block materials. The ability to synthesize structurally and chemically well-defined nanocrystal heterostructures can provide novel combinations of unique properties arising at the nanometer length scale. Here, we examine the structural evolution of inverse spinel iron oxide/CdS nanocrystal heterostructures with respect to the sizes of both components. The crystal structure and the crystallinity of the initial iron oxide are first identified by a combination of X-ray diffraction and Raman scattering measurements. Studies on the size effect suggest lattice-strain-induced limitations on the achievable sizes of CdS within the heterostructures. Because of this limitation, increasing the amount of Cd/S reagents leads to multiple particle nucleation on individual iron oxide nanocrystals rather than continued growth. Larger sizes and a limited amount of the CdS component can be achieved by starting with small iron oxide nanocrystals. These results suggest that exploiting lattice strain may be a viable approach to obtaining heterostructured colloids with nanoscale precision.