SUMMARY

Near-field thermal radiation can exceed blackbody radiation by several orders of magnitude and has potential applications in energy conversion systems, near-field thermal microscopy, and nanomanufacturing. This dissertation is devoted to a thorough analysis of near-field energy transfer at nanometer distances between two semi-infinite plane media. To start with, infrared radiative properties of heavily doped Si are experimentally investigated near room temperature. Accurate carrier mobility and ionization models are identified via a critical review of available literature and then incorporated in to a Drude model to predict the dielectric function of heavily doped Si. The calculated radiative properties of several samples are compared with those measured with a Fourier-transform infrared spectrometer. The improved dielectric function model is then employed to calculate near-field radiative energy transfer between two semi-infinite Si plates using fluctuational electrodynamics. The effects of doping level, polarization, and vacuum-gap width on the spectral and total radiative transfer are studied. An intriguing question in nanoscale thermal radiation has been the existence of an upper limit of the heat transfer between two media as the separation distance is arbitrarily reduced. This issue is addressed here by calculating the maximum achievable near-field heat transfer between two parallel plates separated at very small distances. Initially, frequency-independent dielectric functions are considered to determine what combinations of the real and imaginary parts of the dielectric function will maximize the heat transfer. This is followed by a parametric optimization of the Drude and the Lorentz model for maximum achievable near-field heat transfer in realistic material systems. A better understanding of the surface wave effect on near-field heat transfer is thus obtained. Furthermore, it is found that, unlike far-field radiation, the penetration depth during near-field heat transfer depends on the vacuum gap thickness in addition to material properties. Consequently, a 10 nm thick SiC film can become essentially opaque when the vacuum gap is less than 10 nm. In addition to the calculation of near-field energy transfer between the two media, it is important to understand the direction of energy flow between them. An improved algorithm that is consistent with the fluctuational electrodynamics is developed to correctly trace the energy streamlines, representing the direction of energy flow, inside the emitter, receiver, and the vacuum gap. The results obtained from this research will facilitate the future design of MEMS devices and applications of nanoscale radiation for energy harvesting