(654c) Atomic Layer Deposition of Functional Coatings On Nanoparticles Using a Micro-Jet Assisted Fluidized Bed Reactor
The gas-phase fluidization behavior of nanoparticles has been rapidly developing in recent years. Atomic layer deposition (ALD) is a gas-phase reactive process by which nanoscale functional layers can be chemically bonded to the surfaces of fine particles. ALD is typically performed in stainless steel fluidized bed reactors at temperatures between 100 and 500°C, and under vacuum conditions (~1 Torr). It is well known that shear forces must be imparted to the nanoparticles in order to overcome attractive interparticle forces and break apart large nanoagglomerates which form due to van der Waals and other attractive forces.. Previously, mechanical agitation was delivered to the ALD fluidized bed reactor using a vibrating tray or a stirring unit. A high-pressure micro-nozzle within the bed allows for the delivery of large shear forces and enables the use of glass reactors to monitor the fluidization behavior of powders during ALD processes. Nozzle diameter, pressure and relative flow rate were studied at a variety of conditions to optimize nanoparticle fluidization behavior in the presence of reactive precursors. Since metal oxides are typically deposited using water as an oxygenation source, an in-depth study of the temperature-dependent water removal rate from a jet-fluidized bed reactor is presented. The temperature-dependent implications are discussed in the context of metal-containing precursors that may undergo thermal decomposition at elevated temperatures. The transient fluidization behavior of nanoparticles in the presence of surface reactions is presented for the first time.