超长定向含铁多壁碳纳米管阵列的制备

采用无模板化学气相沉积法,以二茂铁为催化剂,二甲苯为碳源,利用单温炉加热装置制备了定向碳纳米管阵列。运用扫描电子显微镜、透射电子显微镜、拉曼光谱和X射线衍射仪等对定向碳纳米管阵列的形貌、成分和物相进行细致的分析和表征。结果表明:制得的碳纳米管阵列具有良好的定向性和多壁管状结构,并且石墨化程度高;碳纳米管中除碳元素外,管中包含有少量以纳米颗粒和纳米线形式存在的铁及其化合物,主要成分是铁和碳化铁。结合碳纳米管的制备和透射电子显微镜分析表征结果,认为超长碳纳米管阵列的生长模式为底部生长方式,即经历催化剂分解、催化、成核、长大、中毒、凝聚成粒和连接成线的循环过程,正是由于碳源和催化剂的连续供应促成了碳纳米管阵列的快速定向生长。     

化学气相沉积法制备定向碳纳米管阵列

以二茂铁和二甲苯分别作为催化剂和碳源，采用一种无模板的化学气相沉积法，使用单温炉设备，成功地制备了高度定向的碳纳米管阵列.分别用扫描电子显微镜、透射电子显微镜和电子能量散射谱、拉曼光谱对碳纳米管阵列进行形貌观察和表征, 并研究了不同工艺参数对碳纳米管阵列形貌的影响.结果表明：在生长温度为800℃，催化剂浓度为0.02g/mL，抛光硅片上容易获得高质量的定向碳纳米管阵列，在此优化条件下生长的定向碳纳米管的平均生长速率可达25μm/min.     

基于HRTEM和Raman分析定向多壁碳纳米管阵列的生长机理

以二茂铁、二甲苯为前驱体,石英为衬底,在850 oC的管式炉内采用化学气相沉积法制备出了定向碳纳米管阵列. 高分辨透射电子显微镜和拉曼光谱的结果表明：碳纳米管阵列具有良好的定向性和多壁管状结构,石墨化程度高,并且只在表面存在少量单壁碳纳米管.定向多壁碳纳米管阵列的生长模式为“底部”生长模式,即在生长的初期,当催化剂颗粒较小时,析出的碳原子生成了单壁碳纳米管或与其性质类似的多壁碳纳米管(一般层数小于5层);催化剂颗粒逐渐长大后,大量的碳原子析出后生成了普通的多壁碳纳米管,从而形成了单壁碳纳米管只存在于碳纳米管阵列膜表面和多层碳纳米管膜表面与界面的现象.     

阵列碳纳米管的石墨化程度

采用化学气相沉积法制备了阵列碳纳米管薄膜,对阵列碳纳米管的石墨化程度进行了系统研究。利用扫描电子显微镜(SEM)、拉曼光谱(Raman)对样品形貌以及结构进行了表征。探讨了不同实验参数对阵列碳纳米管石墨化程度影响的机理。结果发现,在一定催化剂浓度范围内,催化剂浓度过低时,阵列碳纳米管的石墨化程度较差,而随着催化剂浓度的增加,阵列碳纳米管的石墨化程度逐渐变好;生长石墨化程度较好的阵列碳纳米管需要合适的进液速度,进液速度过低或过高都会使得碳纳米管的石墨化程度变差;此外,生长石墨化程度较好的阵列碳纳米管也需要合适的生长温度,生长温度过低或过高都会使得碳纳米管的石墨化程度变差。     

采用旋转涂膜法制备基底生长的定向碳纳米管阵列

 采用化学气相沉积技术，利用旋转涂膜法制备催化剂基底材料，通过对涂膜过程中的角速度、旋转时间以及基底还原过程中温度的控制改变催化剂颗粒的分布状态，获得了粒径均匀分布的催化剂基底，该基底上催化剂颗粒集中分布在47～62 nm区间，再利用该基底生长出定向碳纳米管阵列。运用扫描电镜、透射电镜、拉曼光谱仪对样品进行了表征。结果表明旋转涂膜法制备的基底平整性好于普通的滴膜法，且较其它基底制备方法具有简单易控、可使催化剂均匀分散等特点。利用该基底制备的碳纳米管阵列定向性良好。     

生长参数对碳纳米管阵列制备的影响

利用化学气相沉积法在沉积铁纳米颗粒的硅衬底上制备了垂直方向高度有序的碳纳米管阵列．扫描电子显微镜的观测发现，碳纳米管阵列的形貌受到若干生长参数的影响，包括催化剂颗粒大小、反应温度和反应气体的分压等．研究发现，当反应温度升高，或反应气体中碳源气体含量增加时，碳纳米管变粗、变短．当催化剂薄膜的厚度减小时，碳纳米管的直径随之减小而纳米管阵列的高度则先增后减，有一个最大值．这些结果表明，碳纳米管的直径和阵列的高度可通过选择合适的反应温度、匀胶机转速和反应气比率来调节．     

GaAs微尖上碳纳米管的制备

采用热化学气相沉积的方法在选择性液相外延方法制备的GaAs微尖上生长碳纳米管。利用扫描电子显微镜以及拉曼光谱对生长的碳纳米管进行表征。结果表明:GaAs微尖在高温下重新结晶成条状梯形GaAs阵列,生长的碳纳米管连接在相邻的GaAs阵列之间,形态规整,具有较好的石墨微晶结构。在此基础上,提出在微尖上生长纳米管的模型,为实现微纳器件互联提供了一种新方法。     

碳纳米管/硅纳米孔柱阵列的场发射性能

"通过热化学气相沉积的方法将碳纳米管生长到硅纳米孔柱阵列衬底上．采用场发射扫描电子显微镜、透射电子显微镜、高分辨透射电子显微镜、拉曼光谱和X射线能谱对所制备的样品形貌、组成进行了分析．结果发现：所制备产物为一种具有面积大、准周期性的碳纳米管/硅巢状阵列复合结构．能谱分析表明碳纳米管仅含有碳元素．对样品进行场发射性能测试表明该结构开启电压为1.3 MV/m,当外加电压为4.26 MV/m,发射电流为5 mA/cm2．由FN公式计算相应的场增强因子约为1.1￡104．碳纳米管/硅纳米孔柱阵列好的场发射性能被归     

电场诱导碳纳米管阵列准直生长的研究

在传统的热化学气相沉积(CVD)的基础上,引入针尖电场,开展了电场对碳纳米管阵列准直性改善的研究。利用扫描电子显微镜(SEM)和Raman光谱两种表征手段,研究了加电场与不加电场两种情况下得到的碳纳米管(CNT)阵列的准直性,证明了电场对碳纳米管阵列准直生长的有效性。文章还对电场诱导碳纳米管阵列准直生长的机理进行了初步的探讨,认为电场使碳纳米管极化是CNT阵列准直生长的主要原因。     

热丝和射频等离子体化学气相沉积法制备定向碳纳米管薄膜

采用热丝和射频等离子体复合化学气相沉积设备(PE-HF-CVD),以CH4、H2和N2为反应气体.在较低衬底温度下(500℃),用简单的催化剂制备方法--旋涂法在硅片上涂覆Ni(NO3)2溶液,经热处理及H2还原后的Ni颗粒为催化剂,在硅衬底上制备出了垂直于硅片且定向生长的碳纳米管薄膜.扫描电子显微镜(SEM)和透射电子显微镜(TEM)结果显示,1 mol/l的硝酸镍溶液旋涂硅片所得催化剂制得的碳纳米管管径为30～50 nm,长度超过4μm,定向性好.并用拉曼光谱(Raman)对不同摩尔浓度Ni(NO3)2溶液条件下制备的碳纳米管薄膜样品进行了表征.     

Fabrication of aligned carbon nanotubes on Cu catalyst by dc plasma-enhanced catalytic decomposition

Aligned multi-walled carbon nanotubes (ACNTs) are deposited using copper (Cu) catalyst on Chromium (Cr)-coated substrate by plasma-enhanced chemical vapor deposition at temperature of 700 °C. Acetylene gas has been used as the carbon source while ammonia is used for diluting and etching. The thicknesses of Cu films on Cr-coated Si (100) substrates are controlled by deposition time of magnetron sputtering. The growth behaviors and quality of ACNTs are investigated by scanning electron microscopy (SEM) and transmission electron microscopy. The different performance of ACNTs on various Cu films is explained by referring to the graphitic order as detected by Raman spectroscopy. The results indicate that the ACNTs are formed in tip-growth model where Cu is used as a novel catalyst, and the thickness of Cu films is responsible to the diameter and quality of synthesized CNTs.     

Synthesis and magnetic properties of aligned carbon nanotubes by microwave-assisted pyrolysis of acetylene

Aligned carbon nanotubes with high quality were synthesized at low temperature by microwave-assisted pyrolysis of acetylene in nitrogen atmosphere. The morphology and structure of the products were characterized by field-emission scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The results indicated that the ACNTs with high crystallinity are densely packed, and some Fe₃C nanoparticles are encapsulated in all parts of carbon tubes. In addition, the effect of the reaction temperature on the morphologies of the CNTs was also studied in detail. Magnetic measurements showed that the Fe₃C-filled ACNTs display ferromagnetic properties at room temperature, and can be easily manipulated by an external magnetic field.     

Study on effects of substrate temperature on growth and structure of alignment carbon nanotubes in plasma-enhanced hot filament chemical vapor deposition system

Alignment carbon nanotubes (ACNTs) were synthesized on silicon substrate coated with Ni catalyst film and Ta buffer layer by plasma-enhanced hot filament chemical vapor deposition using CH₄, NH₃, and H₂ as the reaction gas, and they were investigated by scanning electron microscopy and transmission electron microscopy. It is found that the diameter of the bamboo-structured ACNTs is increased from 62 to 177 nm when the substrate temperature was changed from 626 to 756 °C. Their growth rate is enhanced by the substrate temperature in a range of 626-683 °C and it is reversely reduced with the substrate temperature after the substrate temperature is over 683 °C. Beginning with wetting phenomenon, the effects of the substrate temperature on the structure and growth rate of the ACNTs are analyzed.     

Synthesis of nanoporous silicon carbide ceramics by thermal evaporation process

New nanoporous β-SiC ceramics were synthesized by a simple thermal evaporation method with commercial silicon powder and activated carbon fragments. The results of scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and X-ray diffraction indicated that the microstructure of the β-SiC nanoporous ceramics was uniform and consistent with the pore size of 50-100 nm. The β-SiC nanocrystal grains of 50-200 nm were accumulated together to form a nanopore network. The formation mechanism was attributed to a template synthesis process, in which activated carbon fragments were employed as the template and they reacted with vaporized silicon through a vapor-solid way.     

Using sonochemistry for the fabrication of hollow ZnO microspheres

Hollow ZnO microspheres assembled by nanoparticles have been prepared by a sonochemical synthesis at room temperature using carbon spheres as template. The growth process of the precursor was investigated. The prepared hollow spheres were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM). The diameter of the obtained hollow spheres is about 500 nm, and the walls are composed of numerous ZnO aggregate nanocrystallines with diameters of 90 nm. A possible growth mechanism for the formation of ZnO microspheres has been proposed, in which carbon spheres play a crucial role in the formation of the wurtzite hollow ZnO microspheres. The specific structure of the hollow spheres may find applications in nanoelectronics, nanophotonics and nanomedicine.     

Carbon nanowire made of a long linear carbon chain inserted inside a multiwalled carbon nanotube

A new type of one-dimensional (1D) carbon structure, carbon nanowires (CNWs), was discovered in the cathode deposits prepared by hydrogen arc discharge evaporation of carbon rods. Observation of high-resolution transmission electron microscopy (HRTEM) indicates that a CNW consists of a multiwalled carbon nanotube (MWNT) with a long 1D linear carbon chain (C chain) inserted into its innermost tube of 0.7 nm in diameter. The characteristic Raman peaks of CNWs appeared at around 1850 cm(-1). Raman scattering and HRTEM studies show the formation of a long linear C chain involving more than 100 carbon atoms inside a MWNT. This novel 1D carbon allotrope has potential applications in nanoelectronics, nanomechanics, and nanomaterials.     

非晶空心碳球的制备及生长机制

采用射频等离子体增强化学气相沉积技术,在CH4/H2的气氛中合成了非晶空心碳球.利用SEM,TEM,拉曼光谱对样品的形貌、成分和结构进行了表征.非晶空心碳球的直径在100～800nm之间,分布在弯曲的碳纳米管丛中.非晶空心碳球的生长机制可能为膨胀生长.