Methodology to Characterize Thermal Properties of Thin Film Superconductors Using a DynaCool Physical Property Measurement System

We describe a methodology to characterize heat capacity
C$_{p}$
of 1 µm thick Nb thin films at a temperature range of 60 K to 1.8 K. We used a commercially available relaxation calorimeter device by Quantum Design DynaCool Physical Property Measurement System (PPMS). The mass of thin films is negligible compared to the minimum coarse estimate required by the heat capacity module of the PPMS. To overcome this limitation, a vertical stack of multiple diced substrates of the same material with uniform dimensions of 2.5 mm × 2.5 mm was joined by cryogenically compatible grease to form a stack resulting in a larger effective mass of the target film. The critical behavior of heat capacity in the region of the transition temperature is demonstrated. The heat capacity of Nb thin films was measured by subtracting the total heat capacity of the joining grease and stack of substrate used as addenda. Results in this work prove that a vertical stacking approach is viable for measuring the behavior of deposited thin films.