Two of the most important research directions in the preparation of nanocrystals are the growth of non-spherical quantum-confined structures and nanocrystal heterostructures. Non-spherical structures provide a means of understanding the effect of dimensionality and structural anisotropy on quantum-confined optoelectronic behavior and also introduce new degrees of freedom in engineering nanocrystal-based devices. Semiconductor nanorods have potential technological advantages over spherical nanocrystals in applications such as polarized light emitters [1] and photovoltaics. [2] Preparation of nanocrystal heterostructures enables new combinations of material properties, such as photonic and magnetic properties, to be achieved. This opens up new possibilities for investigating interactions between nanoscale components of different materials, and new technological applications based on combinations of material properties not attainable in homogeneous nanocrystals. Colloidal chemistry provides the basis of a modular approach for integrating different materials and, therefore, different functionalities in these nanocrystal heterostructures.
Anisotropic growth of semiconductors with the wurtzite crystal structure has been achieved using multiple surfactants, exploiting inherent differences in growth rates between differ-
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