THERMOELECTRICAL MICRO-CALORIMETRY AND MICROANALYSIS ON FREESTANDING MEMBRANES

The heat evolution of exothermic reactions and the thermal response to electrical and chemical heating of small volumes of solids and liquid s were studied using thermopiles with free-standing thin-film membrane s. Therefore, the adapted layout of a miniaturized absolute radiometer was used. The chosen arrangement is marked by the combination of high ly sensitive thermopiles with an extreme reduction of parasitic heat c apacity in comparison with conventional calorimeters or sensors. The s ample is in contact with the free-standing membrane only, so a very sm all heat flow to the heat sink of the sensor substrate is guaranteed. A thermopile transducer made from 76 bismuth/antimony thin-film thermo couples was used for the measurement of temperature differences betwee n sample and surroundings. Thin-film heaters of copper and silver were integrated into the microsystem. The average thickness of the whole t hin-film system is less than 5 mu m. Microcalorimetric measurements we re carried out in the temperature range 295-373 K, where thermoelectri cal transducer signals up to 750 mV were observed. Evaporation, meltin g, solidification, redox reactions and enzymatic reactions were tested as examples, where a sample quantity in the nmole range was found to be sufficient.