280665 Manufacturing of Nanostructured Particles Using Atmospheric-Pressure ALD
Core-shell nanoparticles have high potential in heterogeneous catalysis, in energy storage, as biomarkers, and in several other applications. Currently, such particles are mainly synthesized in the liquid phase. We think, however, that it is advantageous to look beyond the commonly used liquid-phase approach for the production of nanostructured particles . Gas phase methods offer several inherent advantages, such as a better potential for scaling-up and the versatility with respect to particle material and size and structure. It will be shown how ALD can be used to produce large amounts of these nanostructured particles.
Nanopowders can be suspended in an upward gas phase, they can be fluidized. In contrast to particles of say 200 mm, nanoparticles are not fluidized individually but as agglomerates: very dilute clusters of around 200 mm consisting of ~1010 primary particles. The very open structure of the nanoparticle agglomerates enables the coating of individual nanoparticles in a fluidized bed. Hakim et al.  demonstrated the coating of individual nanoparticles with ALD in a fluidized bed at rough vacuum. More recently, we demonstrated that these ultrathin coatings on fluidized particles can also be achieved at atmospheric pressure .
As an example, we processed an amount of 100 g LiMn2O4 agglomerates (diameter around 30 mm), consisting of primary particles of 100-500 nm . We coated this material using 5 ALD cycles with alumina (see Fig. 1.) This material can be applied as cathode material in Li-ion batteries. It will be shown that the ALD coating strongly extends the battery lifetime.
One of the strong points of ALD is that is can be used on many different substrates. Figure 2 gives an example of an alumina coating (5 ALD cycles) applied to Pd nanoparticles on large BaSO4 carrier particles, which can be used in catalysis. In addition, a large range of materials can be deposited using ALD. We have, for example, shown the deposition of Pt on TiO2 nanoparticles. In the proposed paper, we will further discuss the fundamental questions related to nanoparticle ALD, and the opportunities for practical applications. Moreover, an outlook will be given to the continuous production of nanostructured particles using ALD.
Fig. 1 TEM photo of a part of a LiMn2O4 particle coated with a thin layer of alumina (5 ALD cycles).
Fig. 2 TEM photo of a part of a BaSO4 carrier particle with Pd nanoparticles on the surface, coated with a thin layer of alumina (5 ALD cycles).
 van Ommen, J.R., Yurteri, C.U., Ellis, N., Kelder, E.M., Particuology 8 (2010) 572-577.
 Hakim, L.F., Blackson, J., George, S. M., Weimer, A. W., Chem. Vap. Dep. 11 (2005) 420-425.
 Beetstra, R., Lafont, U., Nijenhuis, J., Kelder, E.M., van Ommen, J.R., Chem. Vap. Dep. 15 (2009) 227-233.