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

Authors: 
McCormick, J. A., University of Colorado
Weimer, A. W., University of Colorado at Boulder
George, S. M., University of Colorado

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.