(65c) Atomic Layer Deposition of Zinc Oxide in a Fluidized Bed Reactor for Novel Sunscreens and Cosmetics
Thin film deposition techniques have many applications in electronic, semiconductor, and ceramic processes. One such technique is atomic layer deposition (ALD), which can be used to create pinhole-free, thickness-controlled films of metal oxides. While ALD on flats has been extensively studied, the deposition on nanoparticles is fairly novel and merits exploration. A fluidized bed reactor with in situ mass spectroscopy was used to deposit metal oxides onto the surfaces of primary particles. Zinc oxide was deposited by ALD on spherical silicon dioxide particles and high surface area titanium dioxide nanoparticles in order to create novel UV absorbing fillers for sunscreens and cosmetics products. In situ mass spectroscopy allowed for real-time study and control of the ALD process; diffuse transmittance analysis was used to measure the optical properties of the nanocomposite particles. Analysis showed that the bandgap of the deposited zinc oxide shifted nonlinearly with film thickness up to about 5 nm, after which the bulk bandgap of zinc oxide was observed. Mass spectroscopy analysis of the exiting gas stream showed when the reaction product generation terminated, and when unreacted precursor escaped from the bed. This also validated a process control strategy for monitoring particle ALD processes at any scale.