| Description |
The investigation of thermal transport across extremely small vacuum gap distances is of both practical and fundamental significance. Previous theoretical studies have predicted that in the near-field, or when the emitter-receiver separation is less than the thermal wavelength defined byWien's Law, thermal radiation can exceed Planck's blackbody limit by up to several orders of magnitude due to radiation tunneling of evanescent electromagnetic waves. This enhancement has been verified quantitatively by experimental efforts providing exciting opportunities for novel advancements of thermophotovoltaic energy conversion, passive radiative cooling, and nanoscale thermal management. While experimental findings for gap distances above 20 nm have consistently observed good agreement with near-field thermal radiation theory based on the fluctuational electrodynamics framework, the underlying physics of thermal transport at sub-10 nm gaps (i.e., extreme near-field regime) is still in significant debate. Furthermore, minimal experimental effort has investigated thermal transport between the gap and contact regimes to elucidate the radiation-to-conduction transition mechanism. To address these fundamental knowledge barriers, this dissertation is divided into four research objectives: (1) the theoretical evaluation of extreme near-field thermal radiation between a tip and planar surface, (2) development of a measurement platform enabling sub-10-nm tip-plane gap control, (3) quantitative measurement of nanoscale thermal transport using a feedback-controlled nanoheater, and (4) measurement of thermal transport between a tip and planar surface separated by single-digit nanometer vacuum gap distances. The dissertation begins with a literature survey and a general overview of the dissertation organization. Then, extreme near-field thermal radiation is evaluated theoretically using the finite dipole model based on the fluctuational electrodynamics framework. To experimentally evaluate nanoscale thermal transport at sub-10-nm gap distances, a measurement platform to precisely control the tip-plane separation and measure tip-scattered near-field radiation is developed and tested. Afterwards, the capability to quantify tipinduced thermal transport is verified through the combination of on-substrate platinum nanoheaters with temperature feedback control. Lastly, thermal transport between a silicon tip and platinum nanoheater is measured in the near-contact, asperity-contact, and bulk-contact regimes. The outcomes of this dissertation shed light on the fundamental physics of thermal transport across nanogaps as well as providing new avenues for its control. |
