(a) Example image of a large wall particle scraped from the wall of the deposition tube. These particles are large and flat, providing sites for smaller 1 μm particles to grow from or attach to. The yellow inset box is subfigure (b), and the red inset box is subfigure (c). (b) A more magnified image of the wall particle showing smaller, 1 micron spherical particles attached to the wall particle. The red inset box is subfigure (c). (c) A more magnified image of the wall particle, with identifiable spherical particles attached. The green arrow indicates the exposed, smooth area of the wall particle.