Anisotropic Nature of Thermal Transport in Nanoscale Materials

In this work, an equilibrium technique is developed to study the thermal transport in nanomaterials. By directly tracking the relaxation behavior of energy carriers, the developed technique is able to determine the effect of boundary scattering on thermal transport. Since no temperature differential across the material is required to determine its thermal conductivity, the developed technique is applicable to nanomaterials of different shapes and capable of capturing the anisotropic nature of the thermal transport inside. Applying this technique, the thermal transport in several typical nanomaterials—nanofilms, square and round nanowires, and spherical and cubic nanoparticles are studied in detail. A strong anisotropic nature of thermal transport in nanomaterials is observed. For nanofilms and nanowires, the thermal conductivity in the restricted directions (thickness and radial) is smaller than that in the unrestricted direction. This anisotropic nature is more obvious and important when the characteristic size of nanomaterials becomes comparable to or smaller than the mean free path of energy carriers. Our results comparison shows that with the same characteristic size, the shape of the cross section of nanowires has appreciable effect on the thermal transport in the axial direction. For spherical and cubic nanoparticles, little difference is observed between their thermal conductivities.