Atomic layer deposition on particulate materials

Atomic layer deposition (ALD) is an excellent technique to make nanostructured particles: particles of which the surface is either covered by an ultrathin film or by nanoclusters, with applications in e.g. energy and health. This compact review discusses recent developments in the field of applying ALD to particles and powders. ALD—also known under the alternative names molecular layering and atomic layer epitaxy—was already applied to particulate materials decades ago in the former USSR and in Finland. Later on, significant research efforts were devoted to its development in the United States; currently, it is studied worldwide. The most widely used reactor type is the fluidized bed. Since a batch of particles has a very large surface area—especially in the case of very small or porous particles—it is crucial to be efficient with precursor utilization; we discuss efforts in this direction. Moreover, the effects of gas flow rate and temperature are briefly discussed, while the influence of pressure on ALD on particles is also elaborated. A clear impression of the potential of scaling up ALD on particulate materials is presented, both regarding a novel continuous reactor concept—the pneumatic transport reactor—and the economic aspects of processing large amounts of material. We conclude that ALD is suited to produce nanostructured particles with very high precision and in large quantities.