Fundamental understanding of nanoscale heat transfer for thermal conductivity manipulation

Understanding and manipulating heat transfer to our advantages are essential to intentionally design energy-efficient devices and systems and limit deleterious effects of high or low temperatures on system performance. Nano-engineering offers unique opportunities to obtain previously unachievable properties for diverse applications, ranging from thermoelectric energy conversion and thermal insulation that demands ultra-low thermal conductivity to micro-electronics cooling that, in contrast, desires ultra-high thermal conductivity. Meanwhile, nano-engineering also imposes challenges in the scientific understanding because continuum theories break down at such small length scales. Despite significant effort, in-depth understanding of basic thermal transport processes at the nanoscale is limited, impeding the development of novel thermal applications. In this talk, I will present our computational and experimental efforts to deepen our fundamental understanding of nanoscale thermal transport processes and unveil their direct impacts on macroscopic thermal conductivity. I will show examples where we push the lower and higher boundaries of thermal conductivity as well as achieve switchable thermal conductivity and thermal rectification in organic materials.