【作者】 程进；

【导师】 张福学； 邹小平；

【作者基本信息】 北京邮电大学 ， 物理电子学， 2010， 博士

【摘要】 纳米结构材料,因其特殊的纳米结构而具有许多与块体材料不同的特性,使其在物理学、电子学、化学、生物学等领域有许多潜在应用,因而引起了人们的广泛关注。然而要使纳米结构材料真正地走向实际应用,发展成本低、工艺简单、重复性好的制备工艺至关重要。基于此,本论文重点研究和开发制备相关纳米结构材料的简单、成本低、重复性好的工艺,具体的研究内容和相关结论如下：1.研究了乙醇浮动催化化学气相沉积法制备碳纳米结构材料,包括碳纳米纤维,多壁碳纳米管及阵列,单壁碳纳米管,铁填充碳纳米管及阵列。通过研究发现,由催化剂先体二茂铁热解后形成的大小不同的铁催化剂颗粒,在重力和载气粘性阻力的作用下,会发生按尺寸分离的现象,根据这一现象,可实现碳纳米纤维、多壁碳纳米管及阵列(或铁填充碳纳米管及阵列)、以及单壁碳纳米管的同时制备。此外,利用这一工艺制备的单壁碳纳米管是沉积在温度低于400℃的区域,因此可将单壁碳纳米管沉积在不能承受高温的基底上,如ITO玻璃。这一工艺可以较简单的制备单壁碳纳米管薄膜电极,作为染料或量子点敏化太阳能电池的碳对电极。通过增加催化剂先体二茂铁的用量,可制备出铁填充碳纳米管及其阵列,利用振动样品磁强计表征了其磁特性。通过分析得到的磁滞回线,获得了铁填充碳纳米管的矫顽力约为257.05G,铁填充碳纳米管的矫顽力约为589.97G,比多晶铁材料和纳米晶铁材料高很多。2.讨论了多分支型碳纳米纤维的可能形貌,对于Y形碳纳米纤维,有四种基本的可能形貌,对于多方向生长碳纳米纤维可能具有任意整数个分支,在实验中四种Y形碳纳米纤维的基本形貌都观察到了,实验中观察到的多方向生长碳纳米纤维的分支个数有2,3,4,5。这些分支型碳纳米纤维的形成可能与扩散火焰的不稳定有关。为了改善火焰的稳定性,本论文提出了限域稳定扩散火焰法制备碳纳米结构,这种方法是将火焰限定在一定的区域内燃烧,在燃烧区域之外没有火焰,这种火焰具有高稳定性,为碳纳米管的生长提供了稳定的环境。利用这种方法,采用噻吩/乙醇作为燃料,可制备出碳纳米管及阵列和单壁碳纳米管,而且重复性好。3.研究了利用直流电化学沉积法在ITO基底上制备氧化铅纳米棒。与先前利用直流电化学沉积法在不锈钢片上制备氧化铅纳米棒相比,在ITO基底上氧化铅纳米棒的产量明显提高。利用UV-vis吸收光谱表征了氧化铅纳米棒薄膜的光吸收特性,得到氧化铅纳米棒的带隙约为2.85eV。利用沉积在ITO基底上的氧化铅纳米棒薄膜作为染料敏化太阳能电池的光阳极是有效的,基于氧化铅纳米棒薄膜的染料敏化太阳能电池的开路电压约为0.5V。讨论了氧化铅纳米棒的生长机理,利用无水乙醇洗涤初级沉积物的方法,获得了氧化铅纳米棒生成不同阶段的形貌图,基于实验观察,提出了氧化铅纳米棒生长的一个可能的模型。4.提出了利用液相反应法制备氢氧化铅纳米棒。这种方法是基于氢氧化铅不同晶面对无机氯离子吸附能力的不同,使氢氧化铅纳米棒在生长过程中形成择优生长方向,从而快速形成纳米棒。因此在这种方法中,添加氯离子是制备氢氧化铅纳米棒最关键的因素,本论文比较深入的研究了氯离子浓度对产物的影响,并提出了氢氧化铅纳米棒可能的生长模型。利用矢量网络分析仪,对制备的氢氧化铅纳米棒的微波介电特性进行了表征,结果表明氢氧化铅纳米棒对微波吸收很弱,因此氢氧化铅纳米棒可作为多层吸波材料的过度层。最后对全文进行了总结,并对下一步工作方向作了简要讨论。更多还原

【Abstract】 Nanostructured materials have aroused much attention due to their remarkable properties different from bulk materials. They have many potential applications in physical, electronic, chemical and biological field. However, to achieve the pratical application of nanostructured materials, it is important to develop simple, cost-effective and good-reproducibility method to sythesis nanomaterials. Therefore, in this thesis, we emphasize to investigate and develop simple, cost-effective and good reproducibility route to prepare nanoscale materials. The detailed contents, results and conclusions of this thesis are listed as follows:1. The synthesis of carbon nanostructures, such as carbon nanofibers, multi-walled carbon nanotubes and their arrays, iron-filled carbon nanotubes and their arrays, and single-walled carbon nanotubes, by employing ethanol floating catalyst chemical vapor deposition (EFCCVD). Our results show that the formed nanoscale iron particles with different sizes could be seperated and deposited on different position in a furnace tube under gravity and viscous resistance of carrier gas. Utilizing this phenomenon, we can achieve the synthesis of carbon nanofibers, multi-walled carbon nanotubes and arrays (or iron-filled carbon nanotubes and arrays), single-walled carbon nanotubes at the same time. More important, the single-walled carbon nanotubes can be deposited in the low-temperature (<400℃) area at the growth temperature of 900℃in this process. This gives opportunity to deposit the single-walled carbon nanotubes on the substrates that can not suffer from the high growth temperature, such as ITO glass. So, single-walled carbon nanotube film electrodes on ITO glass, which can apply to dye or quantum-dot sensitized solar cell as a carbon counter-electrode, can be easy to obtain by this simple process. Iron-filled carbon nanotubes and their arrays can be synthesis by EFCCVD with a great excess of ferrocene and their magnetic properties are characterized by vibrating sample magnetometer. The obtained iron-filled carbon nanotubes and arrays have an average coercivity of about 257.05 and 589.97G, respectively, which are higher than that for the bulk polycrystalline iron and nanocrystalline iron.2. The possible morphologies of multi-branched carbon nanofibes have been discussed. For Y-shaped carbon nanofibers, there are four basic possible morphologies; for multi-direction carbon nanofibers, the possible number of branch fibers is a positive integer. Interestingly, we have observed these multi-branched carbon nanofibers in our experiments. The number of branch fibers of multi-direction carbon nanofibers is 2,3,4,5 observed in our experiments. The formation of these multi-branched carbon nanofibers may be related to the unstability of diffusion flames. To improve the stability of flames, we develop a new simple method of stably confined diffusion flames (SCDF) to synthesis carbon nanostructures. In this mehod, the flames only burn in a confined space and no flames exists out of this confined space. This confined flame has high stability that can offer a steady condition to grow carbon nanotubes. By employing thiophene/ethanol as fuel for SCDF, carbon nanotubes and their arrays, single-walled carbon nanotubes can be synthesized with good reproducibility.3. The synthesis of PbO nanorods on an ITO substrate by DC electrochemical deposition has been investigated. Compared with previous report on the electrochemical deposition of PbO nanorods on stainless steel substrates, massive PbO nanorods were obtained with good reproducibility. The optical property of the PbO nanorod film is characterized by UV-vis absorption spectrum and the bandgap of PbO nanorods can be inferred to be 2.85eV according to UV-vis absorption spectrum. The PbO nanorod films on ITO glass can be applied to fabricate dye-sensitized solar cell as a light electrode. The open-curcuit voltage of a dye-sensitized solar cell based on PbO nanorod films can reach 0.5V. The growth mechanism of PbO nanorods prepared by DC electrochemical deposition has been discussed. The intermediate state during the formation of PbO nanorods is obtained by a simple washing of primary deposits with absolute ethanol. According to the obsvervation on the intermediate state, we have proposal a possible model to describe the growth of the PbO nanorods.4. A new simple method to synthesize lead hydroxide nanorods by solution-phase reaction has been developed. The growth of lead hydroxide nanorods is due to the adsorption of chloride ions on the certain crystal planes. So, to obtain lead hydroxide nanorods by solution-phase reaction of lead nitrate with alkali, chloride ions is need to be added into lead nitrate solution. The concentration of chloride ions has a dramatic effect on the morphology and microstructure of the precipitates obtained from the lead nitrate and alkali solution, and this effect has been intensively disscussed. Futher more, a possible growth model has been proposed according to our experimental results. The microwave dielectric property of lead hydroxide nanorods is measured by vector network analyzer. The results indicate that lead hydroxide nanorods have a low dielectric loss tangent and they can be applied to fabricate multi-layer microwave absorption materials as transition layers.In the finality, the problems requiring further studies are discussed.更多还原