The Study Of Thermal Transport Properties In Carbon Nanotubes

With the rapid development of nanotechnology, low dimensional carbon nanotubes exhibit many excellent characteristics as tip materials and thus received much attention. Carbon nanotubes are one of potential materials for nanotransistors, nanoscale thermal rectifiers, because of their excellent thermal properties. In the thesis, we investigate phonon thermal transport properties of carbon nanotubes by appling the nonequilibrium molecular dynamics methods. Some important results have been obtained.First of all, we investigate the existence of competition mechanisms for thermal transportation properties in MWCNTs. The results show that the thermal conductivity of MWCNTs is smaller than that of SWCNTs corresponding to the outer tube of MWCNTs, because the increase of cross-sectional area is larger than the increase of thermal conductance of MWCNTs. At the same time, it is quite funny to find that the effect of bending deformation on thermal conductance is greater than the effect of inter-wall van der Waals interactions on thermal conductance, which caused the thermal conductance of MWCNTs is significantly higher than that of SWCNTs. Last but not least, the thermal conductivity of four-wall CNTs is greater than that of the three-wall CNTs, and much higher than that of double-wall CNTs, due to the dominant position of outer tube in the distributions of heat flux. In short, the thermal transport properties of MWCNTs is not controlled by a single variable, but decided by the competitive relationship between these variables. These results are helpful in selecting MWCNTs as candidates for highly efficient thermal conductors in nanoelectronic devices.And then, by using nonequilibrium molecular dynamics methods, we investigate the difference of heat transport properties with pure SWCNT (10,10) and doping in SWCNT (10,10), and the way of doping, impurity percentage effects on thermal transport properties of SWCNT (10,10). The results show that the thermal conductivity of random doping is larger than the thermal conductivity of one-side doping of SWCNT (10,10), at the same temperature. With the increasing of the concentration of silicon impurity atoms, impurity doping methods have little influence on thermal conductivity. Moreover, both impurity concentration and temperature affect thermal conductivity of SWCNT (10,10), the effect of temperature on thermal conductivity is slighter than that of impurity concentration. At the end, the vibration amplitude is inharmonious in SWCNT (10,10), preventing the transmission of heat. But as the impurity concentration increases to 3%, the vibration amplitude of all became discipline. This is because the vibration mode of the impurity plays the leading role.