(319e) Coating FINE Particles With ULTRA Thin FILMS Using Atomic Layer Deposition

Valdesueiro, D., Delft University of Technology
van Ommen, J. R., Delft University of Technology

Atomic Layer Deposition (ALD) is a gas-phase coating technique that can provide fine particles with ultrathin films, typically 1-50 nm. Due to the large value of the specific surface area, fine particles –diameter ranging from 1 nm to 50 µm– are used in a wide range of industrial fields such as electronics, pharmaceutics, energy storage and catalysis. The aim of the coating is to improve the performance of these materials, either by the  activation of the surface of the particles, or protecting them against the environment. 

ALD can deposit uniform inorganic layers [1] by a set of two self-limiting reactions (Fig. 1). The precursors, which are fed into the reactor in subsequent steps, react on the surface of the particles to form a very thin layer of coating material. The final thickness of the coating is controlled by repeating the cycle a desired number of times. This layer-by-layer growth mechanism can also be used to deposit polymeric compounds (Molecular Layer Deposition) [2] or inorganic-organic hybrid compounds [3]. The coating process is carried out in a fluidized bed reactor, which offers high mass and energy transfer, and the possibility to process large amounts of solids.

The production of core-shell particles via ALD has been already applied in fields such as the Li-ion batteries [1] (Fig. 2) or photo-catalysis [4]. Our current work aims at the production of non-permanent coatings to be applied in the controlled release of compounds for food and pharmaceutical applications.

Fig. 1. Schematic representation of the two   ALD half-reactions.

Fig. 2. Li-ion cathode material (LiMn2O4)    coated with 5 cycles of Al2O3 using ALD [1]

1.         Van Ommen, J.R., et al., Scalable gas-phase processes to create nanostructured particles. Particuology, 2010. 8(6): p. 572-577.

2.         Adamczyk, N.M., A.A. Dameron, and S.M. George, Molecular layer deposition of poly(p-phenylene terephthalamide) films using terephthaloyl chloride and p-phenylenediamine. Langmuir, 2008. 24(5): p. 2081-2089.

3.         Yoon, B., et al., Molecular layer deposition of hybrid organic - Inorganic alucone polymer films using a three-step abc reaction sequence. Chemistry of Materials, 2009. 21(22): p. 5365-5374.

4.    Zhou, Y., et al., Optimal preparation of Pt/TiO2 photocatalysts using atomic layer deposition. Applied Catalysis B: Environmental, 2010. 101(1-2): p. 54-60.