Heterostructured Materials with Nanoscale Precision Moonsub Shim, Department of Materials Science & Engineering, University of Illinois, Urbana, IL Anisotropic nanocrystal heterostructure (NCHs) containing two or more distinct crystalline phases provide new opportunities to combine unique properties of nanoscale materials. However, there is no well-established understanding of how the interfaces form and how the overall morphology of NCHs may be controlled. We have exploited coincidence site lattices of Fe3O4 and CdS to achieve anisotropic shapes. Only the favorable interfaces - mainly (111)/(111) for zinc blend CdS or (111)/(0001) for wurtzite CdS - where there are coincidence site lattices form the heterojunction interfaces. Even in these coincidence site lattices, there is a residual lattice mismatch and the interfacial strain increases with the size of each of the components. This increasing strain leads to limitations on the achievable size and the number of nuclei of the second epitaxial phase. This limitation then in turns provides a new handle on control over the morphology of NCHs nearly at the single particle level. Additional control can be achieved by varying the growth rate and the affinity of the surface capping molecules. In particular, we have been able to achieve interesting rod(s)-on-dot geometries of these Fe3O4/CdS NCHs as shown on the right. CdS Fe3O4 Increasing initial Fe3O4 size Increasing CdS growth rate