Experimental investigations on the influence of curvature and materials on near-field thermal radiation

Abstract

The bimaterial cantilever based near-field thermal radiation measurement setup was an experimental breakthrough in the field of near-field thermal radiation. The setup distinguishes itself from other experimental configurations at that time by allowing a direct measurement of the near-field thermal radiation without the need of fitting parameters. Part of this thesis was devoted to improve the measurement setup. The improved measurement setup is then further modified to experimentally investigate near-field thermal radiation between different geometries and materials. To date, the challenges of alignment of two heat-exchanging bodies have limited the existing experimental investigation on near-field thermal radiation to plate-plate, sphere-plate, and tip-plate measurement. However, theoretical calculations predict more interesting phenomenon beyond these three configurations. This thesis presents a method to measure near-field thermal radiation between two microspheres. The procedure to align two microspheres presented in this thesis extends the existing experimental capability, which is limited to sphere-plate configuration. This method can be further used to investigate the effect of different curvatures of the surface, such as two spheres with different radii, and sphere-cylinder. Recent progress on nanoscale radiative heat transfer has generated strong interest in controlling near-field thermal radiation. The ability to control near-field thermal radiation plays a significant role for applying this technology into applications such as radiative thermal diode, transistor, amplifier, and memory devices. Near-field thermal radiation can be tuned by changing carrier concentration. Using a doped silicon sphere, we demonstrate the tuning effect of near-field thermal radiation between doped silicon surfaces. This demonstration shows the potential application of near-field thermal radiation on controlling radiative transfer by modulating carrier concentration.