Thin Sputtered Glass as a Permeation Barrier for Plasma Polymer Shells

We have successfully sputter coated sub-micron layers of quartz onto plasma polymer shells. An agitation mechanism based on an electromagnetic shaker was used. Coatings as thin as 0.4 μm that retain their integrity have been deposited. These coatings have permeation rates against helium at room temperature that are similar to those of thermal quartz. However, the permeation rates to D₂ and argon of coatings thinner than ≈ 2 μm are higher than expected. In contrast, coatings thicker than 2 μm had D₂ half-lives that were long enough to make them useful as a permeation barrier. Diffusion along grain boundaries or through pinholes is a likely reason for the high permeation rates through the thinner coatings. Because plasma polymer becomes thermally unstable near 300°C, these composite shells have to be filled at a maximum temperature of 250°C.