Atomic layer deposition (ALD), in its various forms, is a way of coating a substrate with a thin film using a layer-by-layer (LbL) bottom-up approach. Whilst many of the substrates are larger surfaces, such as electrodes, it is also possible to coat nanoparticles using this route. This is referred to as particle atomic layer deposition, also referred to as particle ALD and p-ALD.
There are many types of (nano)particle that can be coated using particle ALD, from simplistic iron particles to complex hexagonal boron nitride (h-BN) nanoparticles. Various metal-based coatings, from alumina and zirconia to silica, can be used as the deposition agent, including many transition metal oxides.
Properties and Benefits of Particle ALD
Coating particles is known to introduce many beneficial properties, including corrosion resistance, oxidation resistance, a change in the wettability of the particle, increasing the adhesion of particles and viscosity modulation. Many of the benefits fall into two categories- protection against environmental conditions and an improvement of the ordering of the particles, e.g. increasing the packing density within a particulate system.
For particles involved in the fabrication of electrodes, coating them through particle ALD enable them to become stable under many operating conditions, including transition metal dissolution, electrode-electrolyte interactions, active material instability, high-temperature operations, fast cycling rates and overvoltage conditions.
In a similar way to the production of coatings on larger, and flat, substrates, particle ALD provides a coating that can conform around the whole particle(s), producing an even distribution of coating across all the particles with a given system. These coatings are inherently stable to all kinds of environments and possess a pin hole free surface.
The associated benefits and property enhancements produced through the particle ALD process are a great asset for both new and existing commercial applications and materials.
The Particle ALD Mechanism
In a similar fashion to non-particle ALD, particle ALD involves the complete conformation of the surface of a particle. This is independent of the shape and size of the particle and is grown by a nucleation growth approach.
The surface of the particle is exposed to two ALD precursor materials, commonly referred to as precursor A and precursor B, as they vary depending on the composition of the coating. In general, the surface of a particle is exposed to particle A, this reacts with the particle’s surface, but not with itself.
Once the first reactant has been removed, precursor B is deposited onto the surface and reacts with the functional groups on the surface of precursor A. Both reactions are sustained until all the active sites have been functionalized. This happens for many cycles so that a layered coating with the general formula (AB)n is formed on the surface of the particles.
Particle ALD at Forge Nano
Forge Nano is one of the leading particle ALD specialists on the marketplace today and is demonstrated through the licenses, patents, and IP that they hold. Forge Nano use a patented high-throughput Continuous Particle ALD machine, allow the customer to receive a low-cost ALD coating, with no loss of quality.