Sputtered Au–Ta films with tunable electrical resistivity

Abstract

Gold–tantalum alloy films are attractive for hohlraums used in indirect drive magnetized inertial confinement fusion. A high electrical resistivity of over ∼100 µΩ cm at cryogenic temperatures is an essential requirement for allowing an externally imposed pulsed magnetic field to soak through a hohlraum and magnetize the fusion fuel. Here, we systematically study properties of Au–Ta alloy films in the entire compositional range from pure Au to pure Ta with thicknesses up to 30 µm. These films are made by direct current magnetron co-sputtering on planar substrates. Films are characterized by a combination of high-energy ion scattering, x-ray diffraction, electron microscopy, nanoindentation, and electrical transport measurements. Results show that an alloy with ∼80 at.% of Ta forms a metallic glass exhibiting a maximum electrical resistivity of ∼300 µΩ cm with a weak temperature dependence in the range of 5–400 K. The deposition of a film with ∼80 at.% of Ta onto a sphero-cylindrical substrate for hohlraum fabrication is also demonstrated.