Surface-engineered nanoscale diamond films enable remarkable enhancement in thermal conductivity and anisotropy

Nanoscale diamond films have attracted increasing attention due to their great potential for coating and thermal management in nanoscale electronic and opto-electronic devices. However, in strong contrast to the ultrahigh thermal conductivity of bulk diamond, nanoscale diamond films with typical 2 × 1 reconstructed dimer surfaces show rather disappointing thermal characteristics. Here we demonstrate an effective route to significantly enhance the thermal conductivity of nanoscale diamond films via reconstructing their surfaces by forming carbon nanotubes (CNT). For the same film thickness, the film with the CNT-reconstructed surfaces shows a surprising 3-fold enhancement in thermal conductivity compared to that with the typical 2 × 1 reconstructed dimer surfaces. In addition, a large anisotropy in the in-plane thermal conductivity is observed and remarkably, this strong anisotropy can be effectively tuned by varying the film thickness. We further show that the orientation-dependent lifetime of long wavelength phonons is responsible for the remarkable anisotropy in thermal conductivity. The present work underscores the use of surface engineering to manipulate heat transport at the nanoscale, which provides opportunities for developing effective thermal channeling devices.