Dr. Athanasia Kostopoulou
Synthesis and Characterization of Hybrid Nanocrystal Structures with Tailored Properties
Athanasia Kostopoulou
University of Crete, Chemistry Department
and
Foundation for Research and Technology (FORTH), Institute of Electronic Structure & Laser (IESL)
ABSTRACT
Considerable progress in the synthesis of colloidal inorganic nanocrystals has allowed their exploitation in different applications, ranging from electronics to biomedicine. A significant advancement in the syntheses of nanocrystals entails the capacity to afford not only single- but multi- material hybrids. This thesis presents the development of colloidal chemistry protocols and the characterization of a self-assembled secondary structure (nanocluster) and a hybrid multimaterial heterostructure.
The nanoclusters involve a low cytotoxivity assembly of small γ-Fe2O3 nanocrystals (NCs). The colloidal assemblies are ferrimagnetic in aqueous dispersions and composed of crystallographically aligned NCs. The colloid of nanoclusters operates as a tunable photonic crystal under a moderate magnetic field. Their potential in biomedical diagnosis (MRI) and therapy (magnetic hyperthermia) is shown. Due to their tailored magneto-structural characteristics, the intra-cluster magnetic material volume fraction is raised, in turn producing a remarkable improvement of the transverse 1H-NMR relaxivity (4-5 times higher than that of the commercial contrast agent Endorem®) and a much higher Specific Loss Power is attained than that of other rival nanostructures.
The hybrid heterostructure consists of ZnO nanorods uniformly covered by size-tunable Fe@FexOy core-shell nanocrystals. The bi-functional [cf. with near band-edge (NBE) UV fluorescence and ferromagnetism at 300 K] nanomaterial is characterized by an extended surface coverage with small Fe@FexOy nanodomains, where the interfacial coupling across the Fe-core and FexOy-shell generates exchange-bias, mediated by frozen interfacial spins. In the case of a lower coverage density by larger Fe@FexOy domains, the operating Kirkendal effect between the core and the shell suppresses the exchange coupling anisotropy. Importantly, the interfacial interactions between ZnO-Fe@FexOy scale with the degree of surface coverage and a strain-induced blue-shift of the NBE is observed
KEYWORDS
Nanocluster, hybrid heterostructure, magnetic nanocrystals, colloidal chemistry, magnetic resonance imaging, contrast agent, core-shell structure, iron oxide, exchange bias, magnetic hyperthermia.
October 2012