Surface engineering of micro- and nanoparticles is of great importance in fields such as catalysis, energy, sensing and additive manufacturing. For many of these applications particles are required with different bulk and surface properties. A popular technique to achieve this is to coat the particle surface with a nanometer thick layer. Atomic layer deposition (ALD) is known as a reliable technique for covering complex 3D objects with ultrathin conformal coatings. However, to perform ALD on large quantities of powders, the individual particles need to be fluidized or agitated. Fluidized bed reactors are most often used for ALD on particles, but this reactor concept does not seem to be compatible with plasma enhanced ALD, which is advantages for e.g. coating on temperature sensitive polymer particles or deposition of metals and metal nitrides.
At UGent, a rotary reactor was developed to agitate particles, enabling the deposition of conformal coatings by thermal and plasma-enhanced ALD. Particles ranging from nanometer size to millimeter size were successfully coated with layers of Al2O3, TiO2, SiO2, AlN and TiN. The ALD processes were characterized in-situ by means of mass spectroscopy (MS) and optical emission spectroscopy (OES). The composition and conformality of the coatings were evaluated by X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM).
These ultrathin conformal coatings have, for instance, been applied to polymer particles for improving rheology (flowability) or altering the hydrophobicity, and to metallic particles for corrosion prevention.
Our results prove that the developed rotary reactor enables conformal deposition on nano- and micropowders by thermal and plasma enhanced ALD. In this way, surface engineering of such particles can be achieved.