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 mu m 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 D-2 and argon of coatings thinner than approximate to 2 mu m are higher than expected. In contrast, coatings thicker than 2 mu m had D-2 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 degrees C, these composite shells have to be filled at a maximum temperature of 250 degrees C.