Size and Growth Rate Dependent Structural Diversification of Fe3O4/CdS Anisotropic Nanocrystal Heterostructures

To better understand the growth mechanism leading to enhanced anisotropy in nanocrystal heterostructures synthesized from nearly spherical seeds, we have examined various factors that contribute to structural diversification in Fe3O4/CdS systems. Pseudoseparation of nucleation and growth allows us to quantify how the number of heterojunctions formed varies with concentration and the size of the seed nanocrystals. A careful examination of the size dependence of the maximum number of CdS particles that can nucleate per seed nanocrystal suggests strain induced limitations. By increasing the growth rate, we observe an enhancement of spatial anisotropy in rods-on-dot heterostructures without the need for rod promoting capping molecules such as phosphonic acids. Crystallographic details allow us to identify three distinct morphologies that can arise in rods-on-dot heterostructures; due to zinc blende/wurtzite polytypism in CdS. In all three cases, the junction planes contain identical or nearly identical coincidence sites.