A femtojoule calorimeter using micromechanical sensors

TLDR

The authors present a highly sensitive calorimeter that uses a bimetallic micromechanical sensor whose deflection varies with temperature. The device operates by measuring deflection of a bimetallic cantilever, where temperature changes from ambient or absorbed heat cause bending, and its thermal response time determines the minimum detectable energy. In experiments, the sensor achieved a photothermal spectrometer sensitivity of ~100 pW and a minimum detectable energy of 150 fJ, with modeling suggesting ultimate limits of ~10 pW and ~20 fJ.

Abstract

We describe a highly sensitive new type of calorimeter based on the deflection of a ‘‘bimetallic’’ micromechanical sensor as a function of temperature. The temperature changes can be due to ambient changes, giving a temperature sensor or, more importantly, due to the heat absorbed by a coating on the sensor, giving a heat sensor. As an example we show the results of using the sensor as a photothermal spectrometer. The small dimensions and low thermal mass of the sensor make it highly sensitive and we demonstrate a sensitivity of roughly 100 pW. By applying a simple model of the system the ultimate sensitivity is expected to be of the order of 10 pW. The thermal response time of the cantilever can also be determined, giving an estimate of the minimum detectable energy of the sensor. This we find to be 150 fJ and again from our model, expect a minimum value of the order of 20 fJ.