| Carbon nanotubes (CNTs) were considered to be hollow graphene cylinders. With different diameter, carbon nanotubes could be metal, semi-metal and semiconductor, which enabled CNTs to apply in the fields of semiconductor industry. At present, controllable synthesis of CNTs was mainly realized by chemical vapor deposition. Because CNT-growth process contained complicated gas phase reactions and surface reactions, the mechanism of CNT growth by chemical vapor deposition and the optimization of parameters were research focus. Up to now, many experimental and computational work has been done on this subject. In previous research, the researchers took more attention to the surface reactions of CNT growth. The gas phase reactions, however, have not been studied in detailed. When acetylene was used as the carbon source, the reaction temperature is always700℃, under which CNTs was synthesized, accompanying complicated gas phase reaction. These reactions should affect the growth of CNTs.In the second chapter of this thesis, the local heating CVD system was built and the influence of gas phase reaction on the growth of CNTs was studied. Basing on above experiment and simulation, the influence of reaction parameters, catalyst and gas phase reaction on the growth of CNTs was analyzed.With unique helical morphology in nanoscale, carbon nanocoils (CNCs) may have excellent physical properties and may be applied in the fields of nano-electronic and MEMS system. In recent years, the research on the properties of the CNCs just started, which mainly concentrated on the electrical, mechanical and magnetic properties of CNCs. However, the study was not systematical. In this thesis, the thermal conduction in the CNCs, optical property of CNC and the relationship between the electrical property and the structure of CNCs were studied.In the third chapter, the field-emission properties of an individual CNC was investigated. The electron diffraction patterns and Raman scattering spectra for the CNC before and after the field emission showed the improvement of the crystallinity of the CNC. Joule heating induced by the high field-emission current was considered to be the main reason for this result. Furthermore, the tip morphology of a CNC was also modified by laser irradiation. The field emission property of the modified CNC was improved. It was found that the curvature radius of the modified CNC tip was smaller than that of the initial one, which was the main factor contributing to the enhancement of field-emission properties. In the fourth chapter, the spectra of thermal radiation induced by field emission from a single CNC were obtained, from which its thermal conductivity was investigated. By preparing the CNC device, the dependence of resistivity of the CNC on temperature was studied. The thermal conductivity of the CNC was evaluated to be38W/m-K by an one-dimensional thermal conduction model.In the fifth chapter, electrically driven thermal radiation spectra from single suspended CNCs were investigated. The suspended CNC showed thermally excited emission peaks superimposed on the blackbody radiation spectrum in the wavelengths above600nm. It was believed that at least four pairs of energy bands existed around the Fermi energy level and the observed emission peaks were attributed to thermally-excited interband electron transitions in the CNC.In the sixth chapter, the near-infrared photoresponse of a single suspended CNC was investigated. Under the irradiation of a785nm laser beam, the photoresponse was generated in the voltage-biased CNC. At a voltage of50mV, the sensitivity could reach22%and the typical response time was5ms. It was found the photoresponse of the CNC was mainly attributed to the bolometric effect. Because of the increase of Joule heating, the sensitivity reduced with the elevation of the bias voltage. However, the responsivity increased with the increase of the bias voltage, which was opposite to the change of the sensitivity. The maximum responsivity of the single CNC IR sensor was0.22A/W.In the seventh chapter, the relationship between the internal structure of CNCs and the electrical property of CNCs were investigated by a four-wire method. It was found that the room-temperature resistivity of the CNCs annealed at the temperature higher than1273K deceased significantly, compared with pristine CNCs, because of the improvement of crystallinity of CNCs. The change of the resistance of the annealed CNCs with temperature was also studied. From room temperature to about380K, the change of CNC resistance with temperature could be described by an exponential function. From above experiment, the activation energy of the CNCs annealed at various temperature was calculated. It was found that the activation energy decreased quickly when the size of nano-crystallines increased and the amorphous structure between nano-crystallines reduced. Moreover, when the tensile of the CNC was not large, the resistance of the CNC did not change with the expansion of the CNC. |
PDF Full Text Request