Individual Nanoparticle Coating Using Atomic Layer Deposition
Luis F. Hakim, University of Colorado at Boulder, 1111 Engineering Drive ECCH 111 UCB 424, Boulder, CO 80309, Steven M. George, Chemistry and Biochemistry, University of Colorado at Boulder, Ekeley W145B, Boulder, CO 80309, and Alan W. Weimer, University of Colorado, 1111 Engineering Drive, Boulder, CO 80309-0424.
Primary ceramic nanoparticles were conformally coated with nanothick alumina films using Atomic Layer Deposition (ALD). Titania, Silica and Zirconia nanoparticles were uniformly coated in a fluidized-bed reactor at low pressure and under mechanical vibration. This process yields ultrathin films that are conformal, non-granular and pin-hole free with an average growth rate of 1.1 Angstroms per coating cycle. The self-limiting, self-terminating characteristics of ALD allows for a precise control over the film thickness at the atomic level. The coated powders are characterized by transmission electron microscopy (TEM), ex-situ Fourier Transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS). The particle size distribution and specific surface area of nanoparticles is not affected by the ALD nanocoating process. Nanoparticles fluidized as dynamic aggregates that constantly break apart and reform during fluidization. The fluidization of nanoparticles is controlled by the aggregate properties and not by the individual nanoparticles characteristics. Potential applications and improved surface, optical and reactivity properties of coated nanoparticles are discussed.