We have investigated the use of frequency variation in ac calorimetry in the measurement of thermal quantities within controllable distances of the sample heater and thermometer. This technique, useful in studies of heterogeneous samples where only a small part of the sample is of interest, e.g., surfaces, thin films, and interfaces, is applied to study the thermal properties of a test sample made from indium (In) sandwiched between layers of bulk gallium arsenide. We measure and analyze the frequency dependence of the thermal response of the sample, as well as the variation with frequency of the relative size of the anomaly observed at the In superconducting transition. The data are consistent with a model assuming a thermal diffusionhyphen;limited sampling volume.
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