(403b) Coating Nanoparticles by Atomic Layer Deposition in a Rotary Fluidized Bed: Al2O3 Ald on Zro2

Ultrathin and conformal Al₂O₃ films have been grown by atomic layer deposition (ALD) on ZrO₂ particles with diameters of 60 nm and 400 nm using sequential exposures of trimethylaluminum and H₂O.  This Al₂O₃ ALD on gram-scale quantities of high surface area ZrO₂ nanoparticles was performed in a novel rotary fluidized bed reactor.  The rotary fluidized bed reactor consisted of a stainless steel porous metal cylinder that rotated inside a vacuum system.  The nanoparticles were contained inside the porous metal cylinder and the gaseous reactants and products could easily diffuse through the porous walls without particle loss.  A magnetically coupled rotary motion feedthrough rotated the porous metal cylinder and provided a fluidization-like mixing between the particles and the reactants.  The Al₂O₃ ALD films were deposited on the ZrO₂ nanoparticles at 180°C with a growth rate of 1.8 Å/cycle.  The composition of the Al₂O₃ ALD coating was verified using Auger electron spectroscopy, x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.  Transmission electron microscopy (TEM) and BET surface area analysis were utilized to determine the conformality of the Al₂O₃ ALD coating and to check for particle coalescence.  As shown in the TEM image above, the Al₂O₃ ALD film uniformly coats the primary ZrO₂ particles. There was no evidence for any particle coalescence from the BET measurements.