Extraordinary Heat Transfer Within Nanomaterials and Between Structures

 Nanoscale offers great promise for enhanced heat transfer and advanced thermal control by enabling novel material structures and promoting new mechanisms. This dissertation investigates the heat transfer behavior at the nanoscale of both the solid-based heat conduction and the media-less thermal radiation, and their applications in advanced thermal control, including thermal regulation and rectification. We first introduce the novel polyethylene (PE) nanofiber, which shows aligned molecular chains and suppressed intermolecular phonon scattering. We experimentally demonstrate that PE nanofiber is a thermal regulator by its intrinsic structural phase change. We further modify the nanofiber to realize thermal rectification through partial electron-beam irradiation. Then we explore the near-field thermal radiation between subwavelength dimensions. Near-field thermal radiation, the thermal radiation across subwavelength gap distances (generally nanoscale), has proven efficient in enhancing radiative heat transfer via evanescent waves. However, the influence of subwavelength dimensions on near-field thermal radiation remains unexplored, although it has proven non-trivial effect on far-field thermal radiation. To address this issue, we design and fabricate suspended nanodevices to accurately measure the near-field thermal radiation between co-planar membranes with subwavelength thickness. Besides 20-fold stronger thermal radiation than blackbody, we observe weaker heat transfer than the theoretical near-field predictions based on semi-infinite bodies. We investigate the reasons by identifying different near-field mechanisms and evaluating their contributions. We further realize thermal regulation by integrating overlapped nanograting structures into our co-planar nanodevices. Lastly we systematically apply platinum resistive thermometry to platinum heater for in-situ temperature monitoring. We find corrections are necessary for the widely-used thermometry formulas in literature, if it is under high temperature rise. Our work exemplifies the effectiveness of advanced thermal control through mechanisms at the nanoscale and encourages further studies in the physics of nanoscale heat transfer.