Birth and growth of octapod-shaped colloidal nanocrystals studied by electron tomography

The growth of octapod-shaped colloidal nanocrystals is analyzed in detail by electron tomography. The 3D shape of the starting cubic berzelianite Cu 2-xSe seeds is studied, and their evolution into the final structure composed of a sphalerite CdSe core and eight wurtzite CdS pods is followed. The 3D reconstruction shows markedly different shapes of the pods, four of them having sharp tips and four flat ends. Also, the combination of the tomography results with high-resolution and energy-filtered transmission electron microscopy analyses leads to a precise identification of the structure and composition of the final particles. An interpretation of the different shapes of the pod ends is given based on the intrinsic anisotropy of both the sphalerite CdSe and the wurtzite CdS crystal structures and the different reactivity of their facets in the growth environment. © 2011 American Chemical Society.