【作者】 马赫；

【导师】 潘路军；

【作者基本信息】 大连理工大学 ， 光学， 2013， 博士

【摘要】 碳纳米管是由石墨层卷曲而成的中空纳米管,随着直径的不同,碳纳米管可表现出金属性,半金属性和半导体性,这种性质使得了碳纳米管在半导体等领域具有广泛应用。目前,化学气相沉积法是可控生长碳纳米管的主要方法,由于其反应中包含复杂的气相反应和固相反应,所以化学气相沉积法生长碳纳米管的机理及参数最优化一直是人们研究的热点。在这方面,研究人员做许多了实验和模拟工作。但是,人们更多关注碳纳米管生长过程中的固相反应,而对化学气相沉积过程中的气相反应研究较少。本论文的第二章中建立了局部加热化学气相沉积系统并定性地研究了乙炔气相反应对碳纳米管生长的影响。在此基础上,本章还建立了碳纳米管生长的计算流体力学模型,并分析了生长条件,催化剂颗粒及乙炔气相产物对碳纳米管生长的影响。由于碳纳米线圈具有纳米尺度上的特殊形态,使其在纳米电子学,微纳机电系统中具有潜在应用。目前对碳纳米线圈的研究尚处于起步阶段,主要集中于碳纳米线圈的电学特性,力学特性以及磁学特性,但是并不系统完善。本论文从实验上研究了碳纳米线圈的导热特性,光学特性,并进一步研究了碳纳米线圈的电学特性与其结构上的关系。论文第三章研究了场发射对碳纳米线圈结构的影响。由于焦耳热的作用,场发射之后的碳纳米线圈中的sp2品粒尺寸有所增大且晶粒取向趋于一致。此外,本章还研究了激光处理后碳纳米线圈的场发射特性。激光处理导致的碳纳米线圈尖端曲率半径减小和碳纳米线圈表面非晶碳的去除提高了其场发射特性。论文第四章通过单根碳纳米线圈场发射所引起的热辐射光谱研究了单根碳纳米线圈上的热传导。并且,通过制作悬空单根碳纳米线圈器件初步分析了碳纳米线圈的电阻率和温度的关系。在一维热传导模型的基础上,计算得到的碳纳米线圈热导率为38W/m-K。论文第五章研究了悬空单根碳纳米线圈的电驱动热辐射光谱。悬空单根碳纳米线圈的黑体辐射光谱上叠加有发射峰。发射峰的出现是由于热激励高能电子向低能级跃迁所致。因此,在碳纳米线圈的费米能级附近至少存在四对能级。通过测量碳纳米线圈的光致发光谱,发现光致发光谱具有和电致发光谱类似的发射峰,这一结果也支持了文中对碳纳米线圈能带结构的推论。论文第六章研究了单根碳纳米线圈的红外响应特性。当激光功率为90mw时,碳纳米线圈电导变化率最大可达22%。碳纳米线圈器件的响应时间为5ms左右。进一步的实验表明碳纳米线圈光响应的机理主要为热效应。随着电压增加,由于焦耳热的作用激光照射引起的碳纳米线圈电导变化率下降,但是响应率却随之增加,最大的响应率为0.22A/W。论文第七章利用四探针法研究了碳纳米线圈电学特性和其内部结构的关系。相比于未经退火的碳纳米线圈,经过高温退火后,碳纳米线圈的导电特性有明显的改善。但是,当退火温度高于1273K时,结构变化对碳纳米线圈的室温电阻率变化影响较小。此外,本章还研究了各个退火温度下碳纳米线圈电阻随温度的变化并计算了碳纳米线圈的激活能,发现激活能随碳纳米线圈内晶粒的长大和晶粒间非晶成分的减少而快速降低。此外,在碳纳米线圈发生小形变的情况下,碳纳米线圈的电阻基本不发生变化。更多还原

【Abstract】 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.更多还原