Engineering nanoscale phonon and photon transport for direct energy conversion

Nanostructures have a profound impact on the transport of heat and energy by electrons, phonons, and photons. In this paper, we will discuss some of the nanoscale heat transfer effects on phonon and photon transport and their implications for thermoelectric and thermophotovoltaic energy conversion technologies. For example, low thermal conductivity materials with good electrical properties are required in solid-state refrigerators and power generators to achieve high energy conversion efficiency. Various size effects on carrier transport in nanostructures can be utilized to engineer new structures with improved energy conversion efficiency. The thermal conductivity of superlattices will be used to illustrate the phonon transport characteristics in nanostructures. In another example, we will discuss some nanoscale thermal radiation phenomena, such as interference, tunneling, and surface waves, that can potentially be exploited to improve the efficiency of thermophotovoltaic power generation devices.