定向生长碳纳米管阵列的制备及其应用研究进展

碳纳米管在力、热、光、电等方面都显示出独特的性质，受到众多领域专家的广泛关注，而定向生长的碳纳米管阵列的获得具有更深远的科学意义。详细介绍了国内外定向生长碳纳米管阵列的制备方法，重点阐述了化学气相沉积法（CVD）的制备流程和生长机理以及其工艺参数对生成碳管阵列的影响。简要论述了碳纳米管阵列在几个典型应用领域的研究进展。     

阵列式碳纳米管研究进展

阵列式碳纳米管(Aligned Carbon Nanotubes or ANTs)是指碳纳米管垂直于基底生长形成的碳纳米管阵列,在场发射管和生物传感器等领域具有潜在应用价值.介绍了阵列式碳纳米管的主要制备方法和应用.     

垂直定向碳纳米管的化学气相沉积法制备及其应用进展

垂直定向碳纳米管独特的结构和性能使其成为碳纳米管领域的研究热点,而可控制备是其重点研究方向之一。概述了近年来垂直定向碳纳米管的常用制备方法(热化学气相沉积和等离子体增强化学气相沉积)及其影响因素,以及垂直定向碳纳米管在热界面、光电、场发射和传感器方面的研究进展,重点介绍了一些具有优异性能的研究领域以及存在的问题。     

无氢化学气相沉积法制备碳纳米管

采用无氢的化学气相沉积法（CVD）进行碳纳米管的制备技术研究,并成功地制备了由20—φ80nm左右,长度为50-100μm左右的碳纳米管。通过改变气体的流量等影响因素实现了定向碳纳米管薄膜和多层碳纳米管薄膜以及其它各种形态的碳纳米管的制备。采用微区Raman光谱、扫描电子显微镜（SEM）和透射电子显微镜（TEM）等方法对产物的形貌和结构进行了表征,结果表明采用无氢CVD法可以制备出多种形态的碳纳米管。     

单壁碳纳米管的制备及生长特性研究

采用Fe/MgO作为催化剂 ,催化裂解CH4制备了较纯的单壁碳纳米管 ,用TEM和Raman对碳纳米管进行了表征 ,对不同生长温度下制备的碳纳米管Raman径向呼吸振动峰 (RBM)进行了分析 ,研究了生长温度对单壁碳纳米管生长特性和结构特性的影响     

大内径碳纳米管的制备研究

采用化学气相沉积法（chemical vapor deposition）制备碳纳米管．在高温裂解甲烷制备碳纳米管的反应体系中，比较研究了碳酸钠、碳酸钾、碳酸钙和碳酸钡等碳酸盐作为毒物对镍基催化剂和碳纳米管的影响；另外，还考察了裂解温度对碳纳米管的产率和管型的影响。实验中采用气相色谱（gas chromatography）在线检测甲烷的转化率，从而比较镍基催化荆的催化活性；采用透射电子显微镜（transmission electron microscopy）对合成的碳纳米管的外部形貌进行观察。结果发现，无论是从碳纳米管的产率还是形貌，碳酸钠均优于其它几种碳酸盐，内管径可达到70-80nm，另外还发现，750℃为此法制备碳纳米管的最佳裂解温度。     

定向碳纳米管薄膜的制备研究

采用化学气相沉积法制备了定向碳纳米管薄膜,研究了向反应室载入水、氨水对定向碳纳米管薄膜的影响,并用SEM、TEM、XRD对碳纳米管进行了表征。结果表明：向反应室载入水的量增大,定向碳纳米管的长度先增加后减小。载入水的氩气流量为400ml／min,定向碳纳米管的长度1750μm;向反应室载入氨水,得到疏密相间排列的定向碳纳米管薄膜,氨水量增加,定向碳纳米管薄膜的厚度减小。     

定向生长碳纳米管阵列的制备及其应用研究进展

碳纳米管在力、热、光、电等方面都显示出独特的性质,受到众多领域专家的广泛关注,而定向生长的碳纳米管阵列的获得具有更深远的科学意义.详细介绍了国内外定向生长碳纳米管阵列的制备方法,重点阐述了化学气相沉积法(CVD)的制备流程和生长机理以及其工艺参数对生成碳管阵列的影响.简要论述了碳纳米管阵列在几个典型应用领域的研究进展.     

化学气相沉积法制备多壁碳纳米管

以带程序升温装置的管式电阻炉为实验装置,采用化学气相沉积法,在一定的工艺条件下裂解二茂铁与双鸭山精煤的混合物制备出多壁碳纳米管.采用透射电镜、Raman光谱以及X射线衍射技术对碳纳米管产物进行表征,同时研究了碳纳米管的生长机理.     

Fe-Ni双活性金属催化剂制备碳纳米管的研究

利用催化化学气相沉积法,以Fe-Ni双活性金属为催化剂来制备碳纳米管.其中,Fe-Ni双活性金属催化剂由柠檬酸络合法制得.催化剂的组成和碳纳米管的形貌分别用XRD和TEM来进行了表征.实验结果表明,由于催化剂中的活性成分Fe-Ni形成了固溶体,相互之间产生了协同作用,使得其催化性能大大提高,因而由其制备的碳纳米管的产率明显高于由单一活性金属Fe或Ni催化剂所制备碳纳米管的产率.特别当双活性金属催化剂中的Fe的摩尔百分含量为75%时,产率为最高,达到2000%(gCNTs/gcatalyst precursor·h),这约是相同制备条件下,由单一活性金属Fe或Ni所得到碳纳米管产率的6或4倍.     

A possible role of the dipole moment of the catalyst droplet in nanotube growth, alignment, chirality, and characteristics

Why vapor species land on the surface of the nanoparticle seed for nanotube synthesis is a vital question. An investigation has been carried out to find an answer to it. For this, a model of the dipole moment has been developed. A bimetallic alloy (non-alloy, solid solution) exhibiting the shape of a cap has been assumed to function as the nanoparticle seed. Various features of the dipole moment have been examined. The influence of the dipole moment on nanotube synthesis, alignment, chirality, and characteristics has also been studied. Available experiments on the synthesis of carbon nanotubes employing bimetallic catalysts have been compared with the results from calculations. Close correspondence between the two demonstrates that the catalysts may exhibit a dipole moment and have a crucial role in nanotube synthesis and characteristics. The dipole moment has also been employed to determine why some nanotubes grow vertically, while others are bent. Calculated results appear to explain the basic causes for this. These results suggest that the electric field resulting from the dipole moment of catalysts may be important for the vertical alignment of nanotubes. They may attest to the validity of the model and to the existence of a dipole moment in seeds. Although considered for nanotube syntheses, the results may be applicable to other nanomaterials (nanotubes, nanowires, nanodots).     

Effective reinforcement in carbon nanotube-polymer composites

Carbon nanotubes have mechanical properties that are far in excess of conventional fibrous materials used in engineering polymer composites. Effective reinforcement of polymers using carbon nanotubes is difficult due to poor dispersion and alignment of the nanotubes along the same axis as the applied force during composite loading. This paper reviews the mechanical properties of carbon nanotubes and their polymer composites to highlight how many previously prepared composites do not effectively use the excellent mechanical behaviour of the reinforcement. Nanomechanical tests using atomic force microscopy are carried out on simple uniaxially aligned carbon nanotube-reinforced polyvinyl alcohol (PVA) fibres prepared using electrospinning processes. Dispersion of the carbon nanotubes within the polymer is achieved using a surfactant. Young's modulus of these simple composites is shown to approach theoretically predicted values, indicating that the carbon nanotubes are effective reinforcements. However, the use of dispersant is also shown to lower Young's modulus of the electrospun PVA fibres.     

Pulsed plasma-induced alignment of carbon nanotubes

The growth of uniform films of well-aligned carbon nanotubes (CNTs) using pulsed plasma-enhanced chemical vapor deposition is reported here. It is demonstrated that nanotubes can be grown on a certain critical catalyst film thickness and that their alignment is primarily induced by pulsed plasma excitation time. It is, in fact, found that switching the plasma source for 0.1 s effectively turns the alignment mechanism on, leading to a sharp transition between the pulsed plasma-grown straight nanotubes and continuous plasma-grown curly nanotubes. Raman spectroscopy was successfully applied to confirm that, by employing a suitable plasma excitation time, it is possible to obtain the growth of nanotubes with a limited presence of amorphous carbon on the substrate surface. The pulsed biasing technique offers an efficient method to adjust the CNTs' alignment by independent control of the neutral radical and ion fluxes to the surface.     

Electrospinning carbon nanotube polymer composite nanofibers

The unique and exceptional physical properties of carbon nanotubes have inspired their use as a filler within a polymeric matrix to produce carbon nanotube polymer composites with enhanced mechanical, thermal and electrical properties. A powerful method of synthesising nanofibers comprising these polymer composites is electrospinning, which utilises an applied electric stress to draw out a thin nanometer-dimension fiber from the tip of a sharp conical meniscus. The focussing of the flow due to converging streamlines at the cone vertex then ensures alignment of the carbon nanotubes along the fiber axis, thus enabling the anisotropic properties of the nanotubes to be exploited. We consider the work that has been carried out to date on various aspects encompassing preprocessing, synthesis and characterisation of these electrospun polymer composite nanofibers as well as the governing mechanisms and associated properties of such fibers. Particular attention is also dedicated to the theoretical modelling of these fiber systems, in particular to the electrohydrodynamic modelling of electrospinning polymer jets.     

Carbon nanotube guided formation of silicon oxide nanotrenches

The potential applications of carbon nanotubes are varied. Although it has long been known that solid carbon can reduce SiO2 to its gaseous state at high temperatures, exploiting this reaction to pattern surfaces with carbon nanotubes has never been demonstrated. Here we show that carbon nanotubes can act as the carbon source to reduce (etch) silicon dioxide surfaces. By introducing small amounts of oxygen gas during the growth of single-walled carbon nanotubes (SWNTs) in the chemical vapour deposition (CVD) process, the nanotubes selectively etch one-dimensional nanotrenches in the SiO2. The shape, length and trajectory of the nanotrenches are fully guided by the SWNTs. These nanotrenches can also serve as a mask in the fabrication of sub-10-nm metal nanowires. Combined with alignment techniques, well-ordered nanotrenches can be made for various high-density electronic components in the nanoelectronics industry.     

Re-grown aligned carbon nanotubes with improved field emission

In this work, a simple technique to improve the field emission property of multi-walled carbon nanotubes is presented. Re-grown multi-walled carbon nanotubes are grown on the same substrates after the as-grown multi-walled carbon nanotubes are transferred to other substrates using polydimethylsiloxane as intermediation. For the duration of the synthesis of the re-grown multi-walled carbon nanotubes, similar synthesis parameters used in growing the as-grown multi-walled carbon nanotubes are utilized. As a form of possible application, field emission studies show -2.6 times improvement in field enhancement factor and more uniform emission for the re-grown multi-walled carbon nanotubes. In addition, the turn-on field is reduced from 2.85 V/microm to 1.40 V/microm. Such significant improvements are attributed to new emission sites comprising of sharp carbonaceous impurities encompassing both tip and upper portion of the multi-walled carbon nanotubes. As such, this technique presents a viable route for the production of multi-walled carbon nanotubes with better field emission quality.     

Alignment of muscle precursor cells on the vertical edges of thick carbon nanotube films

The development of scaffolds and templates is an essential aspect of tissue engineering. We show that thick (> 0.5 mm) vertically aligned carbon nanotube films, made by chemical vapour deposition, can be used as biocompatible substrates for the directional alignment of mouse muscle cells where the cells grow on the exposed sides of the films. Ultra high resolution scanning electron microscopy reveals that the films themselves consist mostly of small diameter (10 nm) multi-wall carbon nanotubes of wavy morphology with some single wall carbon nanotubes. Our findings show that for this alignment to occur the nanotubes must be in pristine condition. Mechanical wiping of the films to create directional alignment is detrimental to directional bioactivity. Larger areas for study have been formed from a composite of multiply stacked narrow strips of nanotubes wipe-transferred onto elastomer supports. These composite substrates appear to show a useful degree of alignment of the cells.     

石英基底上定向单壁碳纳米管阵列可控生长

以铜为催化剂,甲烷为碳源,采用化学气相沉积法在石英单晶基底上生长定向单壁碳纳米管阵列,分别用扫描电子显微镜、原子力显微镜对其结构进行表征,研究了使用聚合物聚乙烯丙烯酸甲脂（PMMA）分散催化剂对碳纳米管密度和定向性的影响,利用PMMA分散催化剂能提高催化剂的活性,增加定向碳纳米管的密度,使催化剂形成规则的条状,能进一步提高其密度和定向性。采用微加工工艺做成器件,并利用半导体参数测试仪对器件进行了电学测试。     

Fabrication and characteristics of field emitter using carbon nanotubes directly grown by thermal chemical vapor deposition

We experimentally present the effects of vertical alignment and density of carbon nanotubes on the emission current level. For practical display application, we have fabricated the triode type emitter using directly grown nanotubes as emission tip, and characterized their basic field emission properties. The triode type emitter exhibited a turn-on voltage of 37 V and an anode current density of 1.7 μA with gate voltage at 47 V. The vertical alignment of nanotubes does not play a key role in improving the emission properties in triode type nanotubes emitter.     

Growth of phthalocyanine doped and undoped nanotubes using mild synthesis conditions for development of novel oxygen reduction catalysts

Precious metal alloys have been the predominant electrocatalyst used for oxygen reduction in fuel cells since the 1960s. Although performance of these catalysts is high, they do have drawbacks. The two main problems with precious metal alloys are catalyst passivation and cost. This is why new novel catalysts are being developed and employed for oxygen reduction. This paper details the low temperature solvothermal synthesis and characterization of carbon nanotubes that have been doped with both iron and cobalt centered phthalocyanine. The synthesis is a novel low-temperature, supercritical solvent synthesis that reduces halocarbons to form a metal chloride byproduct and carbon nanotubes. Perchlorinated phthalocyanine was added to the nanotube synthesis to incorporate the phthalocyanine structure into the graphene sheets of the nanotubes to produce doped nanotubes that have the catalytic oxygen reduction capabilities of the metallo-phthalocyanine and the advantageous material qualities of carbon nanotubes. The cobalt phthalocyanine doped carbon nanotubes showed a half wave oxygen reduction potential of -0.050 ± 0.005 V vs Hg\HgO, in comparison to platinum's half wave oxygen reduction potential of -0.197 ± 0.002 V vs Hg\HgO.