(421c) Invited - Thermal and Plasma Enhanced Atomic Layer Deposition on Powders and Particles

Surface engineering of micro- and nanoparticles is of great importance in fields such as catalysis, energy and sensing. For many of these applications particles are required with different bulk and surface properties. Atomic layer deposition (ALD) is known as a reliable technique for surface functionalization of powders, by conformally coating the individual particles with ultrathin layers. However, to perform ALD on powders, fluidization or agitation of the particles is required. During the past decades, both batch and spatial ALD reactor concepts have been developed, including fluidized bed, rotary reactors and pneumatic transport.[1] Although fluidized bed reactors are most often used for ALD on particles, this reactor concept is not compatible with plasma enhanced ALD, which is advantageous for e.g. coating on temperature sensitive polymer particles or deposition of metals and metal nitrides.

In this work, we report on a rotary reactor concept that was developed to enable both thermal and plasma-enhanced ALD on powders.[2] 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 may, for instance, be applied for encapsulation, inducing or enhancing catalytic activity, or altering electrical conductivity.

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.