Thick beryllium coatings by ion-assisted magnetron sputtering

Thick (>150 μm) beryllium coatings are studied as an ablator material of interest for fusion fuel capsules for the National Ignition Facility. DC magnetron sputtering is used because of the relative controllability of the processing temperature and energy of the deposits. However, coatings produced by DC magnetron sputtering leak the fuel gas D2. By using ion-assisted DC magnetron, sputtered coatings can be made that are leak-tight. Transmission electron microscopy (TEM) studies revealed microstructural changes that lead to leak-tight coating. Ultrasmall angle x-ray spectroscopy is used to characterize the void distribution and volume along the spherical surface along with a combination of focused ion beam, scanning electron microscope, and TEM. An in situ multibeam optical stress sensor was used to measure the stress behavior of thick beryllium coatings on flat substrates as the material was being deposited.