Calorimetry provides a method of fundamental, thermodynamic characterization. It can give insight to phase diagrams, phase transitions, and general understanding of materials. The benefits of using and studying small samples in calorimetry are many. Samples may be available only in small quantities, have decreasing quality with increasing size, or be costly to produce in large quantities. Reducing the sample size furthermore decreases equilibration times and thermal diffusion distances, thereby improving temperature and time resolution.
Here, I will describe the current efforts to develop a differential, steady-state AC calorimeter for sub-microgram samples. The current design is based on a Si3N4-membrane with thin film heaters and Au-(2.1%)Co vs Cu thermocouples. The calorimeter shows good absolute accuracy down to 1 K and excellent performance with very high relative resolution, DC/C ~ 10-5. The addenda heat capacity is less than 1 mJ/K at room temperature and below a few nJ/K at 1 K.
The physics of AC calorimetry, electronics and instrumentation aspects, and future plans will be discussed.