Magnetron sputter deposition onto fluidized particle beds

A system for sputter deposition of thin (10–1000 nm) metal and ceramic coatings onto vibro-fluidized beds of millions of microparticles has been demonstrated. Coatings are sputtered onto microspheres of various size distributions. Experiments show that the coating deposition rate onto particles decreases with decreasing particle size, for the case of a fixed total bed mass. Factors affecting particle coating thickness also include sputter power and fluidized bed container size. Coating surface morphology is evaluated using scanning electron microscopy. Lower sputter deposition power creates smoother, less porous coatings. Fluidizing parameters, such as vibration amplitude and frequency, are also shown to affect coating morphology. Dual-layer metal-ceramic coatings are also demonstrated using the sputter deposition technique. A dual-layer aluminum/tin-oxide coating is produced on glass microspheres, which are then shown to have distinct reflectance characteristics and colors. A model is developed to estimate coating thickness based on size, shape and number of particles.