Multi-wall effects on the thermal transport properties of nanotube structures.

Understanding the role of inter-layer interactions in multi-walled carbon nanotubes is one of the challenges in the design of potential materials because of their large impact on the physical properties of carbon nanotubes. We focused on the thermal properties of double-walled carbon nanotubes (DWCNTs), which are promising materials due to their high durability and thermal efficiency. We investigated the thermal conductance of DWCNTs by using the nonequilibrium Green's function method, and found that the quadratic temperature dependence of the thermal conductance at low temperatures consisted of three regions with different tendencies. Based on analysis of the transmission coefficients and the distribution of the normal modes, the three nonuniform regions were attributed to the energy shifts of the normal modes at the low-energy region. We examined the mechanism of these energy shifts using the coupled vibration model with the parameters from our simulations, and elucidated the multi-wall effects on the thermal transport properties of the nanotube structures. The effects we found demonstrated the significance of tailoring thermal properties to obtain the desired applications.