Sensitive power compensated scanning calorimeter for analysis of phase transformations in small samples

We have designed and developed a sensitive scanning calorimeter for use with microgram or submicrogram, thin film, or powder samples. Semiconductor processing techniques are used to fabricate membrane based microreactors with a small heat capacity of the addenda, $120nJ∕K$ at room temperature. At heating rates below $10K∕s$ the heat released or absorbed by the sample during a given transformation is compensated through a resistive Pt heater by a digital controller so that the calorimeter works as a power compensated device. Its use and dynamic sensitivity is demonstrated by analyzing the melting behavior of thin films of indium and high density polyethylene. Melting enthalpies in the range of $40–250μJ$ for sample masses on the order of $1.5μg$ have been measured with accuracy better than 5% at heating rates $∼0.2K∕s$⁠. The signal-to-noise ratio, limited by the electronic setup, is $200nW$⁠.