AC Temperature Calorimetry for Thin Films at Low Temperatures

Abstract
An apparatus for heat-capacity measurements of thin films is devised for the temperature range 0.4–3.5 K using ac temperature calorimetry. The total heat capacity of the addenda is about 2×10-9 J/K at 0.5 K and a heat-capacity change as small as ∼5×10-12 J/K is detectable at this temperature. The performance of the apparatus is checked by measuring the superconducting transition of a thin Al film having a thickness of 2040 Å.