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Doctoral theses

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Identifier

000376813

Title

Σύνθεση και χαρακτηρισμός υβριδικών δομών νανοκρυστάλλων με ρυθμιζόμενες ιδιότητες

Alternative Title

Synthesis and characterization of hybrid nanocrystal structures with tailored properties

Author

Κωστοπούλου, Αθανασία Ιωάννης

Thesis advisor

Λαππας, Αλέξανδρος

Reviewer

Τρικαλίτης, Παντελής
Κουτσολέλος, Αθανάσιος

Abstract

Considerable progress in the synthesis of colloidal inorganic nanocrystas 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 Kirkendall 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.

Language

Greek

Subject

Colloidal chemistry

Contrast agent

Core-shell structure

Exchange bias

Hybrid heterostructure

Iron oxide

Magnetic hyperthermia

Magnetic nanocrystals

Magnetic resonance imaging