Non-adiabatic thin-film (chip) nanocalorimetry

To study the kinetics of processes on a millisecond time scale a thin-film nanocalorimeter based on a commercially available microchip (thermal conductivity vacuum gauge, TCG 3880, from Xensor Integration, NL) was constructed. The gauge consists of a submicron silicon nitride membrane with a film-thermopile and a film-heater, which are located at the 100 μm × 100 μm central part of the membrane. Controlled fast cooling is possible in addition to fast heating at essentially non-adiabatic conditions. To allow fast cooling the measurements are performed in an ambient gas atmosphere. It is proved that the maximum rate of the controlled cooling can be achieved with a gas cooling agent, rather than in a system with a solid heat-sink. The advantage of the gauge TCG 3880 is that its central heated region is small enough to be considered as a point source of the heat-flow into the gas, which essentially simplifies the calorimeter calibration. The maximum cooling rate is inversely proportional to the radius of the heated region. The gauge is placed in a thermostat with controlled gas pressure and temperature to be utilized as a device for fast scanning calorimetry of sub microgram samples with sensitivity 1 nJ/K and time resolution ca. 5 ms.