Ferromagnetic Nanostructures by Atomic Layer Deposition: From Thin Films towards Core-shell Nanotubes

摘要

Nickel, cobalt and iron oxide nanotubes were obtained by atomic layer deposition (ALD) into the pores of alumina membranes. Initially, a metal oxide film was grown by the reaction of a precursor vapor of NiCp{sub}2 (nickelocene), CoCp{sub}2 (cobaltocene) or FeCp{sub}2 (ferrocene) with ozone, respectively. Subsequently, the metal oxide film was reduced in hydrogen atmosphere and converted to a metallic ferromagnetic phase with low-degree of surface roughness. In a similar manner, Fe{sub}3O{sub}4 films have also been obtained by the atomic layer deposition of Fe{sub}2O{sub}3 films based on the reaction of water and iron(III) tert-butoxide (Fe{sub}2(O{sup}tBu){sub}6), followed by a hydrogen reduction to Fe{sub}3O{sub}4 after the ALD process. By conformal coating of self-ordered Al{sub}2O{sub}3 membranes, arrays of magnetic nanotubes with diameters down to 30nm and wall thicknesses of less than 3nm have been achieved. The magnetic properties of the nanotube arrays as a function of wall thickness and tube diameter have been studied by SQUID magnetometry. Atomic layer deposition (ALD) was proven to be a very suitable method for the conformal deposition of magnetic thin films in pore structures of high aspect ratio, while offering high uniformity and precise tuning of the layer thickness and the magnetic properties.