Studies On Thermal Conductance Of Carbon Nanotubes

The carbon nanotube (CNT) has attracted researchers'great attention due to its superior electrical, mechanical, thermal and field-emission properties since it has been discovered. People not only study the nature of one-dimensional system through the CNT, but also do extensive works in technology developments and practical applications with its various superior performances.This thesis focuses on the thermal conduction of the CNT. We not only measured and updated the thermal conductivity of the CNT itself, but also further studied the heat transfer properties at the interface of CNTs and other materials.A CNT can be regarded as a seamless tube curled by graphite layers. Theoretical calculations show that the axial thermal conductivity of an individual single-walled CNT is as high as 6000Wm ^-1 K ^-1 . Several research groups measured the thermal conductivity of an individual CNT, but there are significant differences among these experimental results. The main reason is that the thermal contact resistance caused considerable impacts to the measurements. So we designed a non-contact spectral measurement as follows: an individual CNT was grown on a self-designed micro-device, and the middle part of the CNT was suspended and heated by electricity through four electrodes. Using the characteristics that the Raman frequencies of the CNT change with temperature linearly, we determined the temperature difference between the center and the endpoint of the suspended CNT. Then the thermal conductivity of the CNT can be calculated. We have measured the thermal conductivity of an individual single-walled CNT and a multi-walled CNT with the above method, and the values are 2400Wm ^-1 K ^-1 and 1400Wm ^-1 K ^-1 , respectively. This measurement not only can eliminate the impact of thermal contact resistance, but also is applicable to measure the thermal conductivity of other one-dimensional materials.Due to the high thermal conductivity, CNTs are expected to be applied in interface heat transfer. However, the thermal boundary resistance (TBR) between the CNTs and target materials largely restrains the CNTs'high-heat-transfer capability into full play. Withal, we did the experimental and theoretical researches to explore the origin of the TBR, impact factors and application improvements. Through infrared heating and non-contact temperature detecting method, we measured the TBRs between the CNTs and 6 typical metals as well as 6 typical polymers, and found that the CNT-polymer TBRs are obviously less than the CNT-metal TBRs, although the thermal conductivities of the polymers are much lower. Based on the experimental results, the subsequent theoretical analyses show that the interface transmission coefficient is the key factor which affects the TBR. In addition, the TBR is also influenced by the phonon mode matching of the two materials on both sides of the interface. Hence, the measurement results can be interpreted as follows: more low-frequency phonon mode overlapping between CNTs and polymers as well as the high phonon transmission coefficient in low-frequency region results in the lower CNT-polymer TBRs; in addition, less low-frequency phonon mode overlapping between CNTs and metals as well as the very low intermediate and high-frequency phonon transmission coefficient leads to the larger CNT-metal TBRs. The above experimental and theoretical researches may inspire deeper and clearer understandings of the TBRs between CNTs and various materials, and are of great significance for the further improvements and applications of the CNTs in the interface heat transfer field.