Semi-empirical modeling of the sputter deposition of coatings onto spherical capsules

The sputter deposition of coatings onto spherical capsules is accomplished using a chambered substrate platform. Oxides and metal coatings are sputter deposited through a screen-aperture array onto a 0.3–1.2 mm diameter, solid spheres and hollow shells. Each capsule is individually chambered within a larger array. Ultrasonic vibration is used to produce a random bounce of each chambered capsule in order to produce a coating with uniform thickness. Characterization of aluminum-oxide coated, platinum solid spheres and copper–gold layer coated, hollow capsules indicate that uniform coatings can be produced using a screen-apertured chamber as the substrate platform. Potential advantages of this approach compared to open-bounce pans include improved sample yield and reduced surface roughness since exposure to debris is minimized. A semi-empirical process model for the coating growth on the capsules is developed to assess selection of the screen aperture based on the sputtering parameters and the coating materials.