Studies Of The Impact And Modulation On Carrier Transport Properties Of Single-Walled Carbon Nanotubes Induced By Several Typical Intrinsic Defects

Carbon nanotubes (CNTs) have drawn a great deal of attention due to the state-of-the-art potentials in physics and chemistry, material science and nanotechnology since discovered. However, different kinds of defects always exist in process, and these defects can significantly affect the electronic structures and functiinal properties of CNTs. Thus, the studies of the influence of structural defect on the charge tanrsport property of CNTs should be of great significance. This dissertation presented the charge carrier transport properties of zigzag CNTs induced by three typical intrinsic defects, Stone-Wales (SW), mono-vacancy, and doble-vacancy defects, based on the density functiinal theory (DFT). The main factors to affect the carrier mobilities were explored and the rules of the impact and modulation on the carrier transport were obtained.1. The carrier mobilities of zigzag CNTs with SW defects were investigated and compared with those of pristine tubes by using self-consistent field crystal orbital (SCF-CO) method combined with DFT. For the zigzag CNT (11,0) with SW defect, the obtained carrier mobility of several defective tubes are unusuaral increased. This result is further confirmed by the IIV characteristics by means of the non-equilibrium Green’s function (NEGF) method. It was found that the most important reason for the unusual increase in the carrier mobility of defective (11,0) tube is the decreased DP constant, as determined by the weaker acoustic scattering of the carriers. This result can be understood with the aid of crystal orbital analysis. Additionally, the size effect on the carrier mobility induced by SW defects was considered. It was observed that the increased mobility presents a 3-fold periodic pattern for zigzag CNT (n,0) with n= 9-17 and that is similar to the three distinct groups of electronic structures for CNTs.2. First-principle investigations were conducted to study the charge carrier mobility of (10,0) carbon nanotubes with mono vacancy defects under the condition of structural evolution. Although the carrier mobilities of some defective structures are decreased, unexpected enhancement for the electron mobility occurs as the defect B introduced into (10,0) tube. The influence of the defects on the carrier mobility is understood with the aid of crystal orbital analysis. It is found that the most important factor for the increased carrier mobility is the weaker acoustic scattering caused by the defects. As to the decreased mobility, it is mainly due to the heavier carriers derived from the localized wave-functions induced by the defect. Thus the modification of the carrier mobility of the zigzag (10,0) tube can be achieved by the intruduction of mono vacancy defects with different structures.3. The carrier mobilities of zigzag CNTs induced by mono vacancy defects under the condition of the qutntum size effect of CNTs with different diameters were investigated by using the first-principle SCF-CO method. It is found that the carrier mobilities of CNTs (n,0) n= 9-17 changed different with different diameters. Although the carrier mobilities of some defective structures are decreased as expected, some defective structures are increased. The decreased carrier mobility is mainly due to the heavier carriers.And from the crystal orbital analysis, it is found that the most important factor for the increased carrier mobility is the weaker acoustic scattering caused by the defects.4. The carrier mobilities of zigzag CNTs (n,0) n=7-15 with double vacancy defects by means of the DFT combined with SCF-CO method. For the zigzag CNT (14,0) with double vacancy defects, the obtained carrier mobility are increased compared with those of the pristine tube. It found that the main factor leading carrier mobility increased is the weaker acoustic scattering caused by the defects by the crystal orbital analysis.We also considered the effect of size on the carrier mobility induced by double vacancy defects,it is found that some defective structures are decreased and some increased.The reason of increased mobility is similar with CNT (14,0).