Nanoengineering heat transfer performance at carbon nanotube interfaces.

Carbon nanotubes are superb materials for nanoscale thermal management and phononic devices applications, due to their extremely high thermal conductivity (3000-6600 W/mK) and quasi-one-dimensional geometry. However, the presence of interfaces between individual carbon nanotubes as found widely in nanocomposites, nanoelectronics, and nanodevices severely limits their performance for larger scale applications. Solving this issue requires a deep understanding of the heat transfer mechanism at this nanoscale interface between low-dimensional structures, where conventional models developed for interfaces in bulk materials do not apply. Here we address this challenge through a bottom-up approach based on atomistic simulations. We demonstrate that the huge thermal resistance of carbon nanotube junctions can be significantly improved through modifying the molecular structure at the interface to enhance both the matching of phonon spectra and phonon mode coupling. Specifically, two approaches based on polymer wrapping and metal coatings are investigated here and have shown to improve both the structural stability and interfacial thermal conductivity of carbon nanotube junctions. By properly designing the interface molecular structure between individual carbon nanotubes, significant performance gains up to a factor of 4 can be achieved. These results pave the way for future designs of thermal management networks and phononic devices with thermally transparent and structurally stable interfaces.