【作者】 赵元春；

【导师】 孙连峰；

【作者基本信息】 中国科学院研究生院（国家纳米科学中心） ， 凝聚态物理， 2008， 博士

【摘要】 本文研究、优化了浮动催化化学气相沉积法制备单壁碳纳米管的生长参数,可控地制备出几种不同形貌的单壁碳纳米管并开展了相应的物性研究。在此基础上,开展了单壁碳纳米管器件的设计、构建以及电学输运特性研究。另外,利用气相沉积方法制备了富氮的碳氮微纳米线。主要内容如下:1.利用浮动催化CVD方法制备了三种不同形貌的单壁碳纳米管:单根单壁碳纳米管、单壁碳纳米管网格和单壁碳纳米管膜;利用不同的手段研究了单壁碳纳米管样品的形貌、结构和管径分布。在硅基底上制备了规则排列的金图案,并使同一根单壁碳纳米管同时沉积在硅和金的表面。拉曼光谱研究结果表明:与普通拉曼散射相比,表面增强拉曼散射能够更有效地实现对单根单壁碳纳米管的探测和表征。2.以PMMA光刻胶作为牺牲层,制备了悬空的单根碳纳米管器件;并在室温和低温下研究了碳纳米管器件的电学输运特性,观测到了半导体性碳管器件p/n型电导的双极性行为和明显的库仑振荡现象;测量结果表明碳纳米管-金属电极间的肖特基势垒对悬空碳纳米管器件的电学输运性质有着重要的影响。利用聚焦离子束技术将器件中单根碳管的两端开口,分别在真空和水蒸气气氛下研究了开口单根碳管的电学性质。通过一种经过改进的四电极方法从实验上证明:水可以进入到开口的单壁碳纳米管中,碳管的自由载流子与管内极性水分子存在一定程度的相互耦合;在外加电场的作用下,碳管内定向运动的载流子通过这种耦合引起水分子的定向运动。而水分子的定向运动可以在同一碳纳米管的另一部分导致载流子的运动和积累,从而建立起一个稳定的电动势。这说明水填充的单壁碳纳米管可以用作电能和水流动能的转换器。3.利用金刚石拉丝模对所制备的单壁碳纳米管膜进行后处理,得到了高密度、定向排列的碳纳米管样品。这种样品以单壁碳纳米管为结构单元构成了二维三角格子,晶格常数为19.62 ?;由于单壁管之间的距离与石墨层间距类似,在碳纳米管晶体中首次观测到尖锐、峰位与石墨(002)峰接近的衍射峰。同时,拉曼散射研究发现碳纳米管晶体中的呼吸模与原始的碳纳米管膜呼吸模相比存在明显的区别:在碳纳米管晶体中,较大管径碳管的呼吸模受到明显的抑制。碳纳米管晶体具有较大的密度、较小的电阻率和优良的光电导性能。4.对化学气相沉积方法进行了改进,采用具有较高热稳定性的碳氮粉末作为前驱物,在较低的实验温度下首次实现了富氮碳氮微纳米线的大规模制备。获得的碳氮微纳米线具有大的长径比和较好的石墨层状结构,样品表现出典型的sp2价键特征,并且在蓝绿光波段具有荧光特性。我们提出了富氮碳氮一维结构的气-固生长模型,并且认为在热蒸发过程中由碳氮原子组成的杂苯环(C3N3)及其衍生结构没有被破坏,而是作为基本的结构单元在温度和气流合适的位置沉积并生长成一维结构,从而保证了产物具有高的含氮量。实验结果对制备高含氮量的碳氮纳米结构和富氮掺杂的碳纳米管具有一定的指导意义。更多还原

【Abstract】 In this thesis, we have optimized the parameters of floating catalytic chemical vapor deposition (FCCVD) technique, and prepared single-walled carbon nanotubes (SWNTs) with several different morphologies. Their related physical properties have also been investigated. Meanwhile, we have fabricated suspended SWNT devices, and measured the electrical transport properties of the devices. Moreover, we have reported the large-scale synthesis of the nitrogen-rich carbon nitride micro/nanofibers. The main results of this thesis include the following four parts.Firstly, by using FCCVD method, we synthesized SWNTs with three different morphologies: individual SWNTs, SWNT networks and SWNT films. The morphology, structure and diameter distribution of the as-prepared SWNT products were characterized by using several techniques. Individual SWNTs were directly deposited on Au-patterned Si substrates, which allowed us to carry out comparative studies on surface-enhanced Raman scattering (SERS) and normal Raman scattering (NRS) from the different segments of an individual SWNT. It suggested that SERS is powerful for detecting Raman signals from individual and isolated SWNTs.Secondly, we directly deposited individual SWNTs on the Si/SiO2 substrates covered with a ~100-nm-thick polymethylmethacrylate (PMMA) film, and then used them to fabricate suspended SWNT devices. Electrical transport properties of the SWNT devices were investigated at both room temperature and low temperature. Ambipolar behavior was measured in some of the semiconducting SWNT devices, and Coulomb oscillations were also observed when experimental temperature was below 60 K. Our results indicated that Schottky barrier between nanotube and metal electrodes was significant for the electrical properties of the suspended SWNT devices. Moreover, we used focused ion beam (FIB) to open both ends of the SWNT in the nanotube device, and thus water molecules can enter the inner channel of SWNT when the device is exposed to the water vapor. As a voltage/current was applied on one part of the SWNT, an electromotive force was clearly detected along the other part of the same nanotube. We suggested the electromotive force can be induced by the mutual coupling between the free charge carriers of the SWNT and the water dipoles inside the nanotube channel. Thus, individual water-filled SWNTs can be used as hydroelectric power converters.Thirdly, the prepared SWNT films were post-treated by using a series of diamond wire drawing dies, and the obtained SWNTs were highly dense and perfectly aligned. X-ray diffraction (XRD) indicated that the highly dense and perfectly aligned SWNTs (HDPA-SWNTs) formed a two-dimensional triangular lattice with the lattice constant of 19.62 ?. A sharp (002) diffraction peak was also observed. Raman spectra revealed that the radial breathing modes (RBMs) of nanotubes with larger diameters in the HDPA-SWNTs were remarkably suppressed. The HDPA-SWNTs have large density, low resistivity and excellent photoconductance properties.Finally, we reported the first synthesis of the nitrogen-rich carbon nitride micro/nanofibers via a thermal evaporation method. Our successful synthesis is attributed to both the high thermal stability of the carbon nitride precursor and the lower experimental temperature, which allowed the CNx (x > 1) nucleus in the precursor remain stable during vapor transfer. They acted as the basic units for one-dimensional structure assembling, and thus made the produced micro/nanofibers nitrogen-rich. The products had graphitic structure, and exhibited sp2 hybridized bonding feature. Blue photoluminescence was observed with a broad full width at half maximum (FWHM), which was closely related to the high nitrogen content and weekly ordered structure of the micro/nanofibers. Our development of a vapor-phase synthesis should be helpful for synthesizing other nitrogen-rich nanostructures and nitrogen-doped carbon nanotubes.更多还原