Fusion Science and Technology / Volume 49 / Number 4 / May 2006 / Pages 721-727
Technical Paper / Target Fabrication
The surface of vapor-deposited polyimide (PI) coating onto a mechanically agitated mandrel has always been rougher than the NIF standard. The roughness has been attributed to various sources, including defects and contamination on substrate mandrels, abraded damage from mechanical agitation, or off-stoichiometric compositions.
At near-stoichiometric deposition conditions, the surface roughness is primarily due to damages from collisions. Using a plastic mesh container with a suitable opening size and synchronized gentle tapping, we have greatly improved the surface quality of 1 mm diameter 4-5 m thick polyimide shells. The plastic mesh improves the surface quality by limiting shell movements and reducing the impact force and number of collisions between the shells during coating. The surface smoothness of the as-deposited polyamic acid coating meets the NIF surface smoothness standard. Appropriate pressure and heat profiles are used to remove the mandrel and convert the thin polyamic acid coating into polyimide and preserve the surface smoothness. The AFM spheremaps, patch scans and WYKO optical interferometer measurement showed a root-mean-square smoothness ranging 3-5 nm.