Nanojoule Thermal Transfer in Micromechanical Heterostructures

We describe recent experiments on heat-transfer processes in silicon-nitride micromechanical heterostructures using nanoscale-science techniques. The influence of various media surrounding the structures, such as ethanol, air, and vacuum, on heat loss is discussed. Key factors investigated are thermal response time and thermomechanical sensitivity. Both the effects of ohmic and laser-irradiated heating are discussed. Using a heterostructured micromechanical calorimeter, heat-transfer processes at phase transitions are determined down to the nanojoule levIn recent years, micromechanical sensors that combine very high sensitivity with short response times and compact size have attracted significant attention. Heterostructured sensors based on the ``bimetallic'' effect are able to detect heat down to 1~pJ. Combined with their short response time (ms), the technique demonstrates a new approach to the thermal analysis of very small samples. In this contribution we describe experiments with our bimetallic micromechanical sensor in vacuum, gas, air, and liquid environments. We further demonstrate its application to the thermal analysis of picoliter volumes of solid materials BBimetallic micromechanical sensors were first reported in the study of the chemical reaction of hydrogen and oxygen to form water over a catalytic Pt layer in high vacuum. From those experiments, a temperature resolution of 10**(-5)~K was estimated. Such devices are theoretically able to detect heat changes with attojoule sensitivity.