Seeded Growth of Asymmetric Binary Nanocrystals Made of a Semiconductor TiO2 Rodlike Section and a Magnetic γ-Fe2O3 Spherical Domain

Asym. binary nanocrystals (BNCs), comprising one c-axis elongated anatase TiO2 section and one γ-Fe2O3 spherical domain attached together, are synthesized by heterogeneous nucleation of iron oxide onto the longitudinal facets of TiO2 nanorods in a ternary surfactant mixt. The topol. controlled compn. of the BNCs is ascertained by a combination of powder X-ray diffraction, Raman and Moessbauer spectroscopy, high-angle annular dark-field imaging, and high-resoln. TEM lattice fringe mapping, while their size-dependent magnetic behavior is demonstrated by a.c. susceptibility measurements. The heteroepitaxial growth proceeds through a mechanism never obsd. before for colloidal nanoheterostructures: the two domains share a restricted and locally curved junction region, which accommodates efficiently the interfacial strain and retards the formation of misfit dislocations. It is believed that these BNCs, which combine the properties of two technol. relevant oxide materials, can pave the way to reinforced applications in several fields of nanoscience, such as in photocatalysis, in malignant cell treatments, and in nanocrystal assembly.