A femtojoule calorimeter using micromechanical sensors

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.

Fabrication and characterization of a micromechanical sensor for differential detection of nanoscale motions

“…We estimate from the maxima of the slopes of the two curves that the differential measurement is approximately 50 times less sensitive to temperature changes than the absolute measurement. The temperature sensitivity of a cantilever with the material and geometric properties reported here is calculated as 70 nm C [12]. Accordingly, the differential thermal sensitivity is calculated as 1.4 nm C. In a system using a single cantilever, bending induced by a 1 C temperature change could easily exceed that caused by a typical biological reaction.…”

“…In bending experiments with single cantilevers [1]- [6], [12], the ambient temperature has to be controlled precisely during the experiment to avoid bending due to the temperature sensitivity of the cantilevers. In addition, controls to determine the specificity of the bending have to be done sequentially using different cantilevers.…”

Peer Reviewed: Microcantilever Transducers: A new Approach in Sensor Technology

“…This application took advantage of the extremely low heat capacity of the micromachined suspended bi-material structure and the subnanometer accuracy of cantilever deflection measurements using the optical lever method. With AFM optical cantilever readout, the device had the potential to detect 1 pJ of thermal energy and 10 -5 K of the local temperature difference (30). Using this approach and a modified AFM instrument, researchers could detect enthalpy changes associated with phase transitions in nanogramsize samples.…”

Novel uncooled infrared detectors

“…Thermomechanical detector approach was pioneered by Barnes et al when they coated microcantilevers with a metal as the sensing active layer to form the bimaterial [36]. Figure 3 shows a schematic diagram of the capaci− tively sensed microcantilever structure.…”

“…Between them, the most important are bimaterial microcantilevers that mechanically respond to the absorp− tion of the radiation. These sensing structures were origi− nally invented at the Oak National Laboratory (ORNL) in the mid 1990's [11][12][13][14][15], and subsequently developed by ONRL [16][17][18][19][20], the Sarnoff Corporation [21,22], Sarcon Microsystems [23][24][25] and other for imaging [26][27][28][29][30][31][32][33] and photo spectroscopic applications [34,35].…”