Insights into the Structure of Dot@Rod and Dot@Octapod CdSe@CdS Heterostructures

CdSe@CdS dot@rods with diameter around 6 nm and length of either

20, 27, or 30 nm and dot@octapods with pod diameters of ?15 nm and lengths of ?50

nm were investigated by X-ray absorption spectroscopy. These heterostructures are

prepared by seed-mediated routes, where the structure, composition, and morphology of

the CdSe nanocrystals used as a seed play key roles in directing the growth of the second

semiconducting domain. The local structural environment of all the elements in the

CdSe@CdS heterostructures was investigated at the Cd, S, and Se K-edges by taking

advantage of the selectivity of X-ray absorption spectroscopy, and was compared to pure

reference compounds. We found that the structural features of dot@rods are

independent of the size of the rods. These structures can be described as made of a

CdSe dot and a CdS rod, both in the wurtzite phase with a high crystallinity of both the

core and the rod. This result supports the effectiveness of high temperature colloidal

synthesis in promoting the formation of core@shell nanocrystals with very low

defectivity. On the other hand, data on the CdSe@CdS with octapod morphology suggest the occurrence of a core composed of

a CdSe cubic sphalerite phase with eight pods made of CdS wurtzite phase. Our findings are compared to current models

proposed for the design of functional heterostructures with controlled nanoarchitecture.