Fabrication of Fe3O4-ZnO core-shell nanoparticles by rotational atomic layer deposition and their multi-functional properties

Abstract

Fe3O4-ZnO core-shell nanoparticles (NPs) were fabricated using a flow-type atomic layer deposition (ALD) apparatus, equipped with a rotational reactor. This overcomes problems with aggregated NP cores that are commonly encountered when fabricating core-shell NPs by conventional ALD. The composition, crystallographic, optical, and magnetic properties of the NPs were investigated for multifunctional applications. Diethylzinc and deionized water were used as the metal precursor and oxidant, respectively, for preparing the ZnO shells by ALD. The ALD process used in this study differed from conventional ALD processes, in that it included extra evacuation and reaction steps for coating NP cores with shells. The evacuation and reaction processes allowed the precursor and reactant to sufficiently react with the large surface area NPs. The thickness of the shell was controlled by varying the ALD cycle parameters. The morphology and crystallinity of the ZnO shells were investigated by high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy mapping. The X-ray powder diffraction pattern of the Fe3O4-ZnO NPs indicated the formation of ZnO shells of wurtzite structure on the Fe3O4 cores. The stoichiometry of the ZnO shells was analyzed by X-ray photoelectron spectroscopy. Photoluminescence and magnetization measurements of the Fe3O4-ZnO NPs showed that they simultaneously exhibited photoluminescence from ZnO and superparamagnetism from Fe3O4.