Boundary scattering effect on the thermal conductivity of nanowires

Tuning the surface boundary structures of crystal nanowires (NWs) is one of the most popular ways to control the thermal conductivity of NWs. In this paper, non-equilibrium molecular dynamic simulations (NEMD) and time domain normal mode analysis (TDNMA) are performed to investigate the thermal transport properties of Ar (length of 52.9 nm, width of 4.23 nm) and Ge (56.5 nm long and 4.52 nm wide) NWs with different surface boundary structures. Results show that both the total and modal thermal conductivity have a dramatic difference among the NWs with the same diameter (the maximal and minimal thermal conductivity of Ar (Ge) NWs are 1.25 (15.3) and 0.60 (5.64) W/mK, respectively), which suggests the efficiency of nanoscale thermoelectric devices and heat dissipation devices can be largely tuned by only changing the boundary orientation. The fundamental mechanism responsible for such a discrepancy is found to mainly originate from different phonon group velocity (combined with phonon relaxation time for Ar NWs). The results are quite helpful for understanding the boundary scattering effect on thermal transport and also facilitating the design of nanoscale devices by tailoring the boundary structures.