Thermoelectrical micro-calorimetry and microanalysis on free-standing membranes

Abstract

The heat evolution of exothermic reactions and the thermal response to electrical and chemical heating of small volumes of solids and liquids were studied using thermopiles with free-standing thin-film membranes. Therefore, the adapted layout of a miniaturized absolute radiometer was used. The chosen arrangement is marked by the combination of highly sensitive thermopiles with an extreme reduction of parasitic heat capacity in comparison with conventional calorimeters or sensors. The sample is in contact with the free-standing membrane only, so a very small heat flow to the heat sink of the sensor substrate is guaranteed. A thermopile transducer made from 76 bismuth/antimony thin-film thermocouples was used for the measurement of temperature differences between sample and surroundings. Thin-film heaters of copper and silver were integrated into the microsystem. The average thickness of the whole thin-film system is less than 5 μm. Microcalorimetric measurements were carried out in the temperature range 295–373 K, where thermoelectrical transducer signals up to 750 mV were observed. Evaporation, melting, solidification, redox reactions and enzymatic reactions were tested as examples, where a sample quantity in the nmole range was found to be sufficient.