Membrane-based microcalorimetry for thin films and sub-milligram single-crystal

We report on the design, fabrication and use of micro-machined, membrane-based calorimeters for heat capacity measurements in the 20 K < T < 300 K temperature range. The membrane is made of Si3N4 and its thickness is as small as 250 nm. Thermometer and heater are fabricated in Pt by sputtering and optical lithography. Remarkably, the addenda of our devices are three to four orders of magnitude smaller than the most commercially performing available calorimeters. This leads to a high sensitivity, making them suitable for addressing samples in the form of thin films and sub-milligram single-crystals. Automated measurements are performed using a custom-made programme based on the quasi-adiabatic thermal relaxation method. A sample measurement is taken for a Na-Mn-O sub-milligram, and the results are reported so as to compare with the expected signal.