Particle coating, through-porous and HAR structures
|Pictures by VTT (2010)|
As a gas-phase, surface-controlled and self-saturating method, ALD is an optimal technique to coat the whole inner and outer surface area of particles, powders, porous and three-dimensional structures. ALD can be used to functionalize the particles or alter/control their basic physicochemical properties, passivate them, ensure corrosion/moisture/oxygen protection, or attach the particles to a substrate. A special application when it comes to ALD particle coatings are catalysts. One of the main requirements for an efficient catalyst is high active surface area. Nanoparticle powders fulfill this requirement, and in order to save materials and costs, with ALD only the particle surface needs to be coated with the actual catalyst when the particle core can be made of some significantly more cost-efficient material. Catalytically active platinum group metals can be deposited either as individual particles or continuous thin films on the entire surface of catalyst support. Additionally, the particle size of metals on the surface can be tailored with ALD. Top-flow distribution of precursor gases allows gases to flow through the particle bed in Picosun's specifically designed POCA sample holder which maximizes precursor contact with the active surface area of the particles. PICOFLOW™ diffusion enhancer can also be utilized to lengthen the time the precursors stay in the reaction chamber and thus, the reacting time to realize the best possible coating results.
Through-porous or high aspect ratio (HAR) samples such as microchannel plates, deep trenches and through silicon via structures can be effectively coated in PICOSUN™ reactors due to forced flow and, if needed, boosting the diffusion and lengthening the time the precursor gases stay in the reaction chamber with the PICOFLOW™ diffusion enhancer.