Investigation of nanoscale thermal radiation : theory and experiments

Abstract

The ability to control the radiative properties of objects is of prime importance in diverse areas like solar and thermophotovoltaic energy conversion, narrowband thermal emitters, and camouflage in military applications. Thermal radiation at the nanometer scale is significantly different from classical or macroscopic radiative energy transport - wave effects, such as interference and diffraction, and near-field effects play a significant role. By modeling thermal radiation as governed by Maxwell's equations and relating the source of thermal radiation to temperature induced fluctuations of electric currents, it becomes possible to capture the nanaoscale effects that differrentiate it from classical blackbody radiation. This work is focused on two aspects of nanoscale thermal radiation - the ability to tailor the emissive properties using 1D photonic crystals and the enhancement of radiative heat transfer due to electromagnetic surface waves. Theoretical investigation of thermal radiation in ID photonic crystals led to the proposal of new type of selective emitters using 1D metallo-dielectric photonic crystals that rival the more intricate 2D and 3D counterparts.

(cont.) In addition to far-field spectral control, near-field enhancement due to surface phonon polaritons is shown to be useful for enhancing the power density of thermophotovoltaic energy conversion. The difficulties of experimental investigation of near-field phenomena between macroscopic parallel surfaces led to the theoretical investigation of near-field effects between two spheres and experimental investigation between a sphere and a flat plate. A new technique for measuring the radiative transfer between a sphere and a substrate using a bi-material atomic force microscope cantilever as the sensor was developed. By measuring "heat transfer-distance" curves, just as one measures "force-distance" curves in atomic force microscopy, the experimental results are shown to be in agreement with a theory.