Title: Bi-material microcantilever-based thermal sensing techniques
Description: Understanding thermal transport at the nanoscale has important implications for state-of-the-art engineering systems. Thermal management in electronic devices and nanostructuring of devices for thermoelectric energy conversion are two examples of important engineering problems which will benefit directly from improved understanding of nanoscale thermal transport. To this end, development of new techniques in thermal metrology is key to the advancement of this research topic. The ability to sense smaller magnitudes of heat transfer than currently possible will enable us to measure thus-far elusive phenomena such as the effects of molecular chain alignment on thermal conductivity in polymer nanowires, or even heat transport through single molecules. Bi-material cantilevers act as thermometers. A beam, made up of two material layers, will bend due to thermal stimuli because of the mismatch in thermal expansion coefficients for the two material layers. If the dimensions of the cantilever are scaled down to yield a bi-material microcantilever, this can be an extremely sensitive thermal sensor.

This thesis focuses on the development of bi-material microcantilever based thermal sensing for the study of nanoscale heat transfer. A microcantilever design optimized for thermal sensitivity is presented, along with a reliable process for fabrication of such sensors. With these optimized cantilevers, we can push past the picowatt-limit and measure sub-picowatt heat fluxes. In order to harness the high thermal sensitivity of these cantilevers for the purposes of thermal conduction measurements, a new measurement technique which we call the dual-cantilever technique is introduced, whereby a nanostructure is suspended between two cantilevers and thermal conduction measurements can be performed on this single nanostructure. Thermal measurements on single polymeric nanowires are performed to show the effectiveness of this method. The theory for the thermal and mechanical models of the dual-cantilever scheme is developed to corroborate the effectiveness of the technique. Making use of versatile and highly sensitive bi-material microcantilever sensors, this thesis seeks to enhance the measurement methods available for the study of nanoscale thermal transport effects.