Ion beam sputter deposition onto levitated and stalk mounted laser fusion targets

Abstract

Ion beam sputter deposition has been used to coat both levitated and stalk mounted hollow glass microballoon (GMB) laser fusion targets. GMBs levitated with a focused molecular beam were coated with Cu at pressures which ranged from 0.020 Pa (0.15 mTorr) to 0.13 Pa (1.0 mTorr). Stalk mounted GMBs were coated with Cu, Fe, Ta, or Mo at pressures from 0.0050 Pa (0.038 mTorr) to 0.10 Pa (0.75 mTorr). Beam energies of 300–1000 eV and beam current densities of 4–8 mA/cm2 were used. Scanning electron micrographs of fractured cross sections of the coatings were examined for film structure and surface smoothness. As the deposition pressure was reduced, both Cu and Fe exhibited a transition from zone 1 to zone T growth, in agreement with Thornton’s Structure Zone Model. The Ta and Mo coatings were dense and had surface roughness less than 100 nm at all beam powers and pressures studied.