Synthesis of Photoactive Magnetic Nanoparticles with Atomic Layer Deposition

Iron-based magnetic nanoparticles have been produced by decomposition of iron oxalate powder. The micrometer-size iron oxalate powder was first ground by use of a cryogenic milling process. A titanium dioxide (TiO 2 ) thin film was then deposited on the synthesized iron nanoparticles with an in situ atomic layer deposition (ALD) process at 100 °C with TiCl 4 and H 2 O 2 as precursors. However, because of the high surface area, the iron nanoparticles were unstable and spontaneously oxidized when exposed to H 2 O 2 during the TiO 2 ALD process, thus reducing the magnetic moment of the core particles. As an improvement in the process, prior to the TiO 2 deposition, an aluminum nitride (AlN) film was deposited in situ to coat and passivate the iron core particles. The AlN ALD was performed at 250 °C with trimethylaluminium (TMA) and ammonia (NH 3 ) as precursors. This passivation provided a significant decrease in the iron oxidation as determined by X-ray diffraction and magnetization measurements. Photoactivity of the TiO 2 film was demonstrated by decomposition of methylene blue solution under ultraviolet irradiation.