多层纳米碳管膜的大面积可控制生长

文章介绍了利用化学气相沉积法在Si和石英基片上大面积生长多层碳纳米管膜的研究成果,通过调节生长参数,不仅可以获得高度取向的碳纳米纤维,还可获得不同直径,不同图案的高度取向的碳纳米管膜,取向碳纳米管膜的可控制制备,为研究碳纳米管的物理,化学性能,特别是为碳纳米管场发射平面图像显示器的应用研究,奠定了坚实的基础。     

碳纳米管/金刚石复合材料的场发射特性

采用微波烧结方法制备了碳纳米管/金刚石复合材料。将碳纳米管和纳米金刚石粉末混合后研磨压片,然后在微波等离子气相沉积系统中采用微波烧结。利用扫描电镜对复合材料的表面形貌和微观结构进行了分析,结果显示碳纳米管比较均匀地分散于复合材料中,并在表面形成了发射微尖。利用二极管结构在动态真空室中对复合材料的场发射特性进行了研究,复合材料有较好的场发射特性,电流密度接近15mA/cm2。     

碳、碳氮和硼碳氮纳米管场发射性能的比较研究

采用高温热解法在860℃分别制备出了碳、碳氮和硼碳氮纳米管，提纯后利用丝网印刷工艺分别将它们制备成薄膜，并测试了它们的场发射性能.结果表明：碳纳米管、碳氮纳米管和硼碳氮纳米管薄膜的开启电场分别为2.22，1.1和4.4V/μm，当电场增加到5.7V/μm时，它们的电流密度分别达到1400，3000μA/cm²和小于50μA/cm².碳和碳氮纳米管薄膜的场增强因子分别为10062和11521.可见，碳氮纳米管的场发射性能优于碳纳米管，而硼碳氮纳米管的场发射性能比前两者要差.解释了这三种纳米管场发射性能差别的原因. 关键词： 碳纳米管 碳氮纳米管 硼碳氮纳米管 场发射     

催化剂对纳米非晶碳膜场发射性能的影响

利用微波等离子体增强化学气相沉积(MPECVD)法,在经处理的单晶硅衬底上沉积了纳米非晶碳薄膜.通过Raman、SEM、XRD表征,研究了催化剂对纳米非晶碳膜的生长速率及场发射性能的影响.结果表明,在制备纳米非晶碳膜时使用FeC13,作为催化剂可大幅提高其生长速率.在相同的制备条件下,与未加FeCl3催化剂制备的纳米非...     

刻线镍膜上沉积的碳纳米管场发射特性

利用微波等离子体化学气相沉积(MWPCVD)方法,在刻线的镍膜上沉积碳纳米管膜。通过SEM和拉曼光谱表征,讨论了催化剂厚度、制备温度、反应时间以及甲烷浓度对碳纳米管场发射的影响。结果表明：不同条件下制备的碳纳米管的场发射性能有很大差异,保持氢气的流量(100sccm)不变,当甲烷流量为5sccm、生长时间为5min、催化剂膜厚为150nm、温度为700～800℃时,场发射性能最好,开启场强为1．3V／um,最大发射电流达到6．8mA／cm^3。     

石墨基底上垂直生长碳纳米管为芯的碳锥结构

采用一种改进的化学气相沉积方法，成功地在石墨基底上自组装生长出以碳锥为支撑的、碳纳米管为芯的新型功能材料.该结构的材料可以用作扫描电子显微镜探针和场发射电子显微镜的针尖.利用电子显微镜研究了不同合成条件对该碳纳米管与碳锥结构生长的影响，给出了最优生长条件，并讨论了生长机制. 关键词： 碳锥 碳纳米管 化学气相沉积 场发射     

连续碳纳米管线及其应用

如何将碳纳米管组装成宏观尺度的结构对于碳纳米管的宏观应用来说具有重要意义．自从碳纳米管被发现以来，在合成大面积碳纳米管阵列方面已经取得很多的进展，并有望应用于场发射平板显示器．然而，在如何将碳纳米管顺排起来连成连续的长线方面则鲜有进展．这里介绍的是作者最近的新发现：当从一种作者称之为“超顺排”碳纳米管阵列中拔出一束碳纳米管时，碳纳米管以可自组织成一条连续的长线．在这个过程中，“超顺排”碳纳米管阵列起的作用如同一个蚕茧，阵列中的碳纳米管则由范德瓦耳斯力首尾相连形成连续的纯碳纳米管线．这种碳纳米管线平行排列起来构成的偏振片可以工作在紫外波段．这种碳纳米管线还可以用作白炽灯的灯丝，仅需很小的功率就可以发出白炽光．不仅如此，这种碳纳米管线经过高温处理后，强度和导电性都得到明显增强，这将使碳纳米管线在宏观领域内得到更多的应用．     

利用胶体小球掩蔽刻蚀技术制备的半导体纳米阵列的场电子发射特性

利用胶体小球掩蔽刻蚀技术,制备了单晶硅纳米阵列,利用原子力显微镜观察了硅阵列的表面形貌,实验结果表明,硅柱阵列具有高密度和较好的均匀性。同时研究了单晶硅纳米阵列的场电子发射特性。为了提高样品的场发射性能,在所制备的单晶硅有序纳米阵列上生长了一层非晶碳薄膜。与单晶纳米硅柱阵列相比,覆盖有非晶碳膜的样品的场电子发射特性有了明显的改善,表现在场发射的开启电场下降,同时场发射增强因子得到增加。结果表明非晶碳膜确实能够降低电子发射的表面有效势垒,从而增强了场电子发射特性。     

高压退火对碳纳米管微结构转变的影响

利用高分辨电子显微镜研究了在高压退火条件下碳纳米管的微结构变化规律，发现在5.5GPa下，770℃退火后即发生了明显的结构改变；在950℃退火25min后发现形成了类碳纳米洋葱和纳米碳条带结构.碳纳米管转变成类碳纳米洋葱可以分成几个步骤，首先碳纳米管破裂，然后形成碳纳米球，最后形成类碳纳米洋葱结构.讨论了高压和退火温度对碳纳米管结构变化的影响. 关键词：     

基片偏压对MCECR溅射硬碳膜特性的影响

采用封闭式电子回旋共振(MCECR)氩等离子体溅射碳靶的方法在硅片上沉积了高质量的硬碳膜, 膜层厚度约40 nm. 使用X射线光电子能谱仪(XPS)和高分辨率透射电子显微镜(HRTEM)分析了碳膜结构,并用POD摩擦磨损仪测试了碳膜的摩擦磨损特性,用纳米压入仪测试了碳膜的纳米硬度.详细研究了基片偏压对碳膜的结构、摩擦磨损特性以及纳米硬度的影响,得到了最佳基片偏压.     

Efficient field emission from coiled carbon nano/microfiber on copper substrate by dc-PECVD

Crystalline coiled carbon nano/micro fibers in thin film form have been synthesized via direct current plasma enhanced chemical vapor deposition (PECVD) on copper substrates with acetylene as a carbon precursor at 10 mbar pressure and 750 °C substrate temperature. The as-prepared samples were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). XRD pattern as well as selected area electron diffraction (SAED) pattern showed that the samples were crystalline in nature. SEM and HRTEM studies showed that as synthesized coiled carbon fibers are having average diameter ∼100 nm and are several micrometers in length. The as-prepared samples showed moderately good electron field emission properties with a turn-on field as low as 1.96 V/μm for an inter-electrode distance 220 μm. The variation of field emission properties with inter-electrode distance has been studied in detail. The field emission properties of the coiled carbon fibrous thin films are compared with that of crystalline multiwalled carbon nanotubes and other carbon nanostructures.     

Electric field aligned growth of single-walled carbon nanotubes

Electric field aligned, single-walled carbon nanotubes are grown between electrodes using thermal chemical vapour deposition (CVD) of methane. The growth occurs on a thin film layered catalyst of aluminium, iron and molybdenum patterned on top of electrodes. The nanotubes bridge 10 μm sized electrode gaps and have a typical diameter of less than 2 nm as measured by Raman spectroscopy and atomic force microscopy. We present electrical transport measurements on a directly grown nanotube which shows p-type semiconducting behaviour.     

Formation mechanism of H2Ti3O7 nanotubes

Formation mechanism of H2Ti3O7 nanotubes by single-step reaction of crystalline TiO2 and NaOH has been investigated via transmission electron microscopy examinations of series specimens with different reaction times and extensive ab initio calculations. It was found that the growth mechanism includes several steps. Crystalline TiO2 reacts with NaOH, forming a highly disordered phase, which recrystallized into some H2Ti3O7 thin plates. H-deficiency on the top surface leads to an asymmetrical environment for the surface Ti3O2-7 layer. The calculations of the surface tension, elastic strain energy, interlayer coupling energy, and Coulomb force indicated that the asymmetrical environment is the principal driving force of the cleavage of the single sheets of H2Ti3O7 from the plates and the formation of the multiwall spiral nanotubes.     

一种平行栅碳纳米管阵列阴极的场发射特性研究

建立一种平行栅碳纳米管阵列阴极,利用悬浮球模型和镜像电荷法进行计算,给出碳纳米管顶端表面电场与电场增强因子的解析式. 在此基础上,进一步分析器件各类参数以及接触电阻对阴极电子发射性能的影响. 分析表明,碳纳米管间距大约为2倍碳纳米管高度时阵列阴极的分布密度最佳,靠边缘部位的碳纳米管发射电子能力比其中心部位的大;除碳纳米管的长径比之外,栅极宽度和栅极间距也对电场增强因子有一定作用;接触电阻的存在大幅度降低碳纳米管顶端表面电场与发射电流,而接触电阻高于800 kΩ时,器件对阳极驱动电压的要求更高. 关键词： 平行栅碳纳米管阵列 悬浮球 场增强因子 接触电阻     

Selective growth, characterization, and field emission performance of single-walled and few-walled carbon nanotubes by plasma enhanced chemical vapor deposition

Single-walled carbon nanotubes (SWCNTs) and few-walled carbon nanotubes (FWCNTs) have been selectively synthesized by plasma enhanced chemical vapor deposition at a relative low temperature (550 °C) by tuning the thickness of iron catalyst. The parametric study and the optimization of the nanotube growth were undertaken by varying inductive power, temperature, catalyst thickness, and plasma to substrate distance. When an iron film of 3-5 nm represented the catalyst thickness for growing FWCNT arrays, SWCNTs were synthesized by decreasing the catalyst thickness to 1 nm. The nanotubes were characterized by field emission scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. Electron field emission properties of the nanotubes indicate that the SWCNTs exhibit lower turn-on field compared to the FWCNTs, implying better field emission performance.     

Field emission characteristic of screen-printed carbon nanotube cathode

The fabrication of carbon nanotube emitters with excellent emission properties is described. The multi-walled carbon nanotubes (MWNTs) produced by chemical vapor deposition (CVD) method were purified with oxidation method and mixed with organic binding pastes and then screen-printed on glass substrates with ITO film. We applied anode voltage gradually to refine the emission behavior of the emitter by cleaning the top surface of screen-printed carbon nanotubes (CNTs). The density of the carbon nanotubes is about 2.5×10⁸/cm². Diode field emission experiments were performed in dynamic vacuum system to study the emission current, the emission uniformity, etc. Bright and stable character emission images were obtained in the diode structure and the emission current could approach 1 mA/cm².     

Synthesis of single-walled carbon nanotubes in mesoporous silica film and their field emission property

We have succeeded in direct synthesis of single-walled carbon nanotubes (SWNTs) on a conductive substrate coated with a 3D mesoporous silica film, and observed the field emission. Co catalysts for the growth of SWNTs are deposited on the substrate by electroplating. The particle size of the catalyst is well-controlled inside defined space of the mesoporous silica film. Furthermore, the location of Co particles can be controlled in the mesopores by the electroplating method. Mono-dispersed SWNTs are grown along with the mesopores that are normal to the substrate, because Co particles are deposited at the bottom of the mesopores. It is also found that the mesoporous silica film prevents the aggregation of Co catalysts and the distortion of Au layer as the conductive substrate. The field emission measurement shows that the turn-on field is 4.2 V/μm at 10 μA/cm². The field enhancement factor is about 1500. This approach provides an efficient methodology for fabricating an SWNTs-based field emitters. PACS 73.63.Fg; 78.55.Mb     

沉积工艺参数对碳纳米管薄膜场发射性能的影响

利用微波等离子体化学气相沉积(MWPCVD)方法,在不锈钢衬底上直接沉积碳纳米管膜。通过SEM、拉曼光谱和XRD表征,讨论了制备温度和甲烷浓度对碳纳米管膜场发射的影响。结果表明:不同条件下制备的碳纳米管膜的场发射性能有很大差异,保持氢气的流量(100sccm)、生长时间(10min)、反应室压力不变,当甲烷流量为8sccm、温度为700~800℃时,场发射性能最好,开启场强仅为0.8V/μm,发射点分布密集、均匀。