Active control of thermal transport is of significant interest for a wide range of applications, such as thermoregulation of individuals, buildings, vehicles and batteries, thermo-electric and solar-thermal energy conversion, bio/chemical sensing, and micro/nanomanufacturing. However, heat transfer processes are often difficult to actively control: heat conduction is usually diffusive in nature owing to the incoherence of heat carriers (phonons and electrons) and thermal radiation is generally broadband or have wide energy distribution. If one could engineer the transport of thermal energy, arguably the most ubiquitous form of energy, with similar degree of controllability as electrical and optical energy, a variety of energy transport and conversion technologies can be improved or even revolutionized. This dissertation presents my work aiming to actively manipulate heat transport with multidisciplinary approaches, including thermo-electric and thermo-photonic engineering.

In the first part of my dissertation, I discuss the strategy for developing flexible thermoelectric materials, which can be used for active thermoregulation of individuals. The ongoing effort to reduce the energy consumption of climate control systems has mainly focused on the development of more efficient thermoregulation technologies. In particular, interests in personalized thermoregulation devices have inspired studies on high-performance flexible thermoelectric materials for integration with emerging wearable electronics. Towards this end, I have developed a generic screen printing strategy using nanostructured thermoelectric materials with optimized printing ink formulation, by considering and satisfying the complex requirements for the printability as well as electrical and thermal transport properties. I used two different approaches, 1) all-inorganic but printable inks and 2) organic-inorganic composite inks.

In the latter part, I introduce a thermo-photonic engineering approach to manipulate nanoscale heat transport by using surface phonon polaritons (SPhP). This dissertation mainly focuses on how the SPhP can be utilized to tailor thermal radiation properties, especially to achieve a coherent, near-monochromatic far-field thermal emission, which is a big departure from the classic textbook incandescent behavior as described by the Planck’s law. The key feature of the design is to utilize nanoscale emitters whose dimension is comparable to or smaller than the thermal wavelength, a regime when the Planckian energy distribution no longer holds (as Planck himself originally noted). Experimental and theoretical work quantify the far-field thermal radiation from these rationally-designed single nano-emitters.