Ion-Beam-Assisted Deposition of Mo Thin Films for TES Applications

Molybdenum/nonsuperconducting metal bilayers form the basis for many high-performance superconducting transition-edge sensors. The low-stress high-density molybdenum films required for this application are usually produced with sputter deposition or evaporation onto a heated substrate to keep the surface mobility of adatoms sufficiently high. However, reproducible and uniform superconducting transition temperatures are difficult to achieve via either technique. As an alternative, we are exploring the use of low-energy (50-150 eV) Ar ion assisted e-beam evaporation to provide an energy/momentum input that can be tuned to optimize film quality. We present measurements of stress, resistivity, and transition temperature of thin (40-100 nm) Mo films deposited over a range of conditions.