Size-dependent phononic thermal transport in low-dimensional nanomaterials

The reduced dimensionality makes low-dimensional nanomaterials possessing diverse unusual size-dependent transport properties, due to the distinct quantum confinement, surface and interfacial scatterings for electron, photon and phonon at the nanoscale. In this review, we summarize the state-of-the-art studies on the topic of size-dependent phononic thermal transport in low-dimensional nanomaterials, including both theoretical and experimental reports. First, the length-dependent thermal transport in quasi-one-dimensional (quasi-1D) and two-dimensional (2D) nanomaterials are discussed, in which the underlying fundamental physics are correspondingly summarized. Then, we review the various effects of transverse dimensions on the thermal conductivity, including the diameter effect in nanowires, and the thickness and width effects in 2D sheets and nanoribbons. Finally, considering the significant importance of interfacial thermal resistance in nanoscale devices due to the increased density of interface, the size effect on the interfacial thermal resistance and thermal rectification is also discussed. The basic concept of phononic engineering to control the interfacial thermal resistance and also the detailed phonon scattering mechanisms are summarized. This perspective review would provide basic and advanced knowledge to understand and utilize the size-dependent thermal transport in nanomaterials, which will be beneficial to the further understanding of energy transport and conversion in the low-dimensional quantum devices.