Absolute accuracy in membrane-based ac nanocalorimetry

► Nanocalorimetry with ac steady-state method. ► We study effect of membrane and sample thermal link. ► We present practical expressions for frequency dependence. ► We study the conditions for good absolute accuracy. ► Measurements are best performed at constant phase. To achieve accurate results in nanocalorimetry a detailed analysis and understanding of the behavior of the calorimetric system is required. There are especially two system-related aspects that should be taken in consideration: the properties of the empty cell and the effect of the thermal link between sample and cell. Here we study these two aspects for a membrane-based system where heater and thermometer are both in good contact with each other and the center of the membrane. Practical, analytical expressions for describing the frequency dependence of heat capacity, thermal conductance, and temperature oscillation of the system are formulated and compared with measurements and numerical simulations. We finally discuss the experimental conditions for an optimal working frequency, where high resolution and good absolute accuracy are combined.