碳纳米管及其包覆结构的电弧法制备和性能研究

IMR OpenIR

	碳纳米管及其包覆结构的电弧法制备和性能研究
	张艳丽
学位类型	博士
导师	成会明 ; 刘畅
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	电弧可控制备碳纳米管纳米电缆场发射 Arc Discharge Controllable Synthesis Carbon Nanotube(Cnt) Nanocables Field Emission
摘要	"理论和实验研究表明碳纳米管具有优异的力学、电学、光学性质，因而在复合材料、纳电子、光电器件等诸多领域有着广阔的应用前景，目前，宏量可控制备高质量的碳纳米管仍然是制约其科学研究和应用发展的瓶颈问题之一。电弧法制备的碳纳米管具有结构完整性好和缺陷少的特点。但由于电弧发生是一个远离平衡态的过程，因此利用电弧法控制生长碳纳米管十分困难。本文改进与完善氢电弧方法，通过原位施加电场、使用新型催化剂及优化反应参数等方法调控碳纳米管的结构及性能。取得的主要研究结果如下：（1）改进制备单壁碳纳米管的电弧放电法。在弧柱区施加125和250 V/cm的直流电场。研究表明：施加电场可以显著提高单壁碳纳米管的产量，并使碳纳米管沿电力线方向定向排列。透射电镜和拉曼光谱研究表明：施加电场后单壁碳纳米管管束尺寸减小，管束尺寸小于10 nm。热重分析表明：原位施加电场制备的单壁碳纳米管的抗氧化温度提高了68 °C，这说明原位施加电场使得碳纳米管结构更加完整，提高了碳纳米管的结晶度。多波长拉曼光谱表征表明：沉积于电极板之外的单壁碳纳米管为金属性富集。（2）以非金属硅为催化剂，制备出具有尖锐端头的碳纳米管。扫描和透射电镜观察表明：尖锐端头碳纳米管主要有锥形、缩颈形和铅笔形三种尖端形貌。尖端直径2-15 nm，底座碳纳米管直径分布较宽，一般在20-130 nm。共振拉曼研究表明：宏量样品中尖锐端头的大量存在，且多为单壁或双壁。这种缩颈形碳纳米管的生长遵循开口生长机制；硅原子的掺杂、无定形炭、相邻碳层间的键合、碳五元环等的引入是形成这些尖锐端头碳纳米管的主要原因。场发射性能研究表明：场发射阈值电场值仅为3.75 V/m；作为单根电子源场发射体时，在1.6×105 A/cm2高场发射电流密度下，经过20 min较长时间的发射过程未发生结构破坏或电流衰减，场发射稳定性优异。这种碳纳米管兼具有较低的阈值电场和稳定性，该优异的场发射性能归结于这种碳纳米管具有良好的结构完整性和独特的尖端结构特征。（3）以铁-钴-镍为催化剂，以炭粉和硅粉的混合物为原料，通过调控生长条件，利用电弧法原位制备出氧化硅包覆单壁碳纳米管的纳米电缆。电镜观察表明：产物中纳米电缆的纯度高，长度达几十微米，直径在20-50 nm之间，包覆层为无定形氧化硅，芯部为1-5根单壁碳纳米管；拉曼光谱分析证明：芯部为单壁管，对纳米电缆的生长机制进行了探讨。该单壁碳纳米管基纳米电缆可望用于构建场效应晶体管器件。"
其他摘要	"Theoretical and experimental studies have shown that carbon nanotubes (CNTs) possess excellent mechanical, electrical, and optical properties, and therefore, CNTs may find applications in a variety of areas, such as composite materials, nanoscale electronic devices, nanoscale optoelectronic devices, etc. Now the controllable, large-scale synthesis of high quality CNTs with specific structures and properties is still one of the key issues in CNTs’ scientific research and application. CNTs obtained by arc discharge usually have good structural completeness and low content of defects. However, the controlled growth of CNTs by arc discharge is quite difficult, since the arc generation is a non-equilibrium process. In this thesis, we controlled the structures and properties of the CNTs by applying external electric field, using novel catalyst, and optimizing the preparation parameters. The main results obtained are as follows: Improved the synthesis of SWCNTs by arc discharge through applying an electric field. A direct current electric field of 125 V/cm or 250 V/cm was applied to the arc column zone. Comparative studies showed that the yield of SWCNTs was largely improved, and the produced SWCNTs were aligned along the direction of the power lines. Characterizations by transmission electron microscopy and laser Raman spectroscopy showed that the mean bundle size of the SWCNTs was decreased to smaller than 10 nm. Thermal gravimetric analysis displayed that the anti-oxidation capability of the SWCNTs was improved (the oxidation temperature was improved by 68 °C), which can be attributed to the better crystallinity of the SWCNTs grown with the electric field exerted. Moreover, multi-wavelength laser Raman spectroscopy study showed that the SWCNTs collected outside the electrode panels were metallic enriched. By using silicon powder as a catalyst, CNTs with a sharp tip were prepared. Scanning and transmission electron microscopy observations revealed that the sharp-tip CNTs have three kinds of tip morphologies, i.e. cone-shaped, suddenly-shrinking, and pencil point-like structure. The diameter of tip part is quite small (2~15 nm), while the diameter of base part is widely distributed (20~130 nm). Resonance raman study verified that large amounts of small tips exist and most of them are single walled or double walled. The growth of CNTs with suddenly-shrinking tips followed open-end mechanism. Dopping of Silicon cluster, introducing of amorphous carbon, bonding of carbon layers, importing of carbon pentagon led to the formation of the sharp-tip CNTs. Study of field emission property of these sharp-tip CNTs showed a low threshold electric field of 3.75 V/m. When served as an electron field emitter, the field emission current was stabilized at around 1.5 mA in a period of 20 min. The desirable field emission performance of the sharp-tip CNTs can be attributed to the good crystallinity and the unique tip structure of the CNTs. Using iron-group metals as catalyst, mixed carbon and silicon powder as raw materials, coaxial nanocables of SWCNTs sheathed with an amorphous silica layer were directly synthesized by arc discharge. Electron microscopy observations showed that the sample was very pure and the nanocables were usually tens of micronmeter in length and about 20~50nm in diameter. The sheathed layer was revealed to be amorphous silica and each nanocable contains one to several SWCNTs in the center part. These SWNT/amorphous silica nanocables may find applications in field effect transistors and other related nanodevices."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64429
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	张艳丽. 碳纳米管及其包覆结构的电弧法制备和性能研究[D]. 北京. 中国科学院金属研究所,2012.