Colloidal Anisotropic ZnO–Fe@Fe x O y Nanoarchitectures with Interface-Mediated Exchange-Bias and Band-Edge Ultraviolet Fluorescence

• Published in: Chemistry of materials 2012-07, Vol.24 (14), p.2722-2732
• Main Authors: Kostopoulou, Athanasia, Thétiot, Franck, Tsiaoussis, Ioannis, Androulidaki, Maria, Cozzoli, P. Davide, Lappas, Alexandros
• Format: Article
• Language: English
• Subjects: Chemical Sciences
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm3008182

Hybrid nanocrystals (HNCs), based on ZnO nanorods (NRs) decorated with magnetic Fe-based domains, were synthesized via a colloidal seeded-growth method. The approach involved heterogeneous nucleation of Fe nanocrystals on size-tailored ZnO nanorod seeds in a noncoordinating solvent, followed by partial surface oxidation of the former to the corresponding Fe@Fe x O y core@shell domains. HNCs with variable population and size of the Fe-based nanodomains could be synthesized depending on the surface reactivity of the ZnO seeds. The structure–property relationships in these HNCs were carefully studied. In HNCs characterized by a large number of small Fe@Fe x O y core@shell nanodomains on the ZnO seed surface, the interfacial communication across the Fe-core and Fe x O y -shell generated a sizable exchange-bias effect mediated by frozen interfacial spins. On the other hand, in HNCs carrying a lower density of comparatively larger Fe@Fe x O y domains, partial removal of the Fe-core created an inner void in between that led to suppressed exchange coupling anisotropy. As a further proof of functionality, the HNCs exhibited pronounced band-edge ultraviolet fluorescence. The latter was blue-shifted compared to the parent ZnO NRs, inferring coupling of the semiconductor and magnet sections.