Hot-wire chemical vapor deposition of carbon nanotubes

Hot-wire chemical vapor deposition (HWCVD) has been employed for the continuous gas-phase generation of both carbon multi-wall and single-wall nanotube (MWNT and SWNT) materials. Graphitic MWNTs were produced at a very high density at a synthesis temperature of 600 °C. SWNTs were deposited at a much lower density on a glass substrate held at 450 °C. SWNTs are typically observed in large bundles that are stabilized by tube–tube van der Waals’ interactions. However, transmission electron microscopy analyses revealed only the presence of isolated SWNTs in these HWCVD-generated materials.     

Structure of multiwalled carbon nanotubes grown by chemical vapor deposition

Carbon nanotubes have been grown by chemical vapor deposition at 650°C in an argon atmosphere using a butane-propane mixture and a nickel catalyst and have been characterized by scanning and transmission electron microscopy and Raman spectroscopy. The results indicate that the multiwalled nanotubes have an imperfect graphite-like structure with a conical supramolecular configuration. A phenomenological technique is proposed for statistical analysis of the state of carbon nanotubes in measurements of the intensity of the defect zone D in their Raman spectra.     

Diameter controlled chemical vapor deposition synthesis of single-walled carbon nanotubes

In this study, we systematically investigated the influence of catalyst preparation procedures on the mean diameter of single-walled carbon nanotubes (SWNTs) synthesized by the alcohol catalytic chemical vapor deposition (ACCVD) process. It was found that the SWNT diameter is dependent upon both reduction temperature and time, with lower reduction temperature and/or shorter reduction time resulting in smaller diameter SWNTs. The morphology of the SWNTs also changed from vertically aligned to randomly oriented when the reduction temperature was below 500 degrees C. We also found that introducing a small amount of water during the catalyst reduction stage significantly decreased the mean diameter of the SWNTs. Lastly, we report on the use of a new binary catalyst system in which rhodium was combined with cobalt. This new Co/Rh combination produced SWNTs of smaller diameter than the conventional Co/Mo catalyst.     

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.     

Catalytic chemical vapor deposition of carbon nanotubes using Ni-La-O precursors

Carbon nanotubes (CNT) are synthesized by catalytic chemical vapor deposition with different compositions of Ni-La-O catalyst precursors obtained by citric acid complexometry. Only two compounds: LaNiO₃ (perovskite-type crystal structure, hexagonal system) and La₂NiO₄ (spinel-type crystal structure, orthorhombic system) in the obtained Ni-La-O catalyst precursors have the ability to grow CNT. Moreover, CNT obtained with the two different crystal structure catalyst precursors have different characteristics: different yield, pattern and oxidation resistance performance.     

Synthesis of phosphorus doped carbon nanotubes using chemical vapor deposition

Phosphorous-doped carbon nanotubes (PCNTs) was prepared via two-step methodology employing chemical vapor deposition, by using available starting materials and catalyst. First, CNTs was produced from acetylene gas at 750 ºC and then, PCNTs have been prepared with total yield of 44% by recooking of the prepared CNT with Ph₃P at 600 ºC. The product was characterized with FESEM, TEM and EDS analyses, which confirmed its nanotube shape and the presence of phosphorous atom. The high thermal stability of the product was obtained from TGA analysis, showing only 16.5% weight loss up to 890 ºC. The Raman spectrum of the product showed the I_D/I_G ration equal to 0.84. Moreover, the catalytic potency of the product has been examined in ORR electrochemical reaction using CV and LSV diagrams. The results confirmed appropriate catalytic activity and high stability of the product for this process.     

改进化学气相沉积法在炭纤维表面生长碳纳米管(英文)

采用一种改进的化学气相沉积法在炭纤维表面制备碳纳米管。为了提高炭纤维表面的润湿性能,炭纤维在浸渍之前先在CVD设备中在真空下973 K的高温处理,然后在硝酸和浓硫酸体积比为3∶1的混合酸中酸处理30 min。而改进的化学气相沉积法关键在于让催化剂的还原步骤和碳纳米管的生长步骤同时进行。这样通过减小过渡金属元素与炭纤维之间的接触时间从而降低了它们之间的相互扩散,在确保了炭纤维本身的力学性能下降程度明显小于用普通化学气相法制备的情况下生长出长且茂密的碳纳米管阵列。另外,经过对工艺参数的优化发现当用乙醇作溶剂,Fe(NO3)3.9H2O溶度为100 mmol/L,氢气和碳源气体比值为4/1,而生长时间为30 min时得到最好的碳纳米管阵列。     

Growth control of carbon nanotubes by plasma enhanced chemical vapor deposition

Plasma enhanced chemical vapor deposition (PECVD), which enables growth of vertically aligned carbon nanotubes (CNTs) directly onto a solid substrate, is considered to be a suitable method for preparing CNTs for nanoelectronics applications such as electron sources for field emission displays (FEDs). For these purposes, establishment of an efficient CNT growth process has been required. We have examined growth characteristics of CNTs using a radio frequency PECVD (RF-PECVD) method with the intention to develop a high efficiency process for CNT growth at a low enough temperature suitable for nanoelectronics applications. Here we report an effect of pretreatment of the catalyst thin film that plays an important role in CNT growth using RF-PECVD. Results of this study show that uniform formation of fine catalyst nanoparticles on the substrate is important for the efficient CNT growth.     

Growth of well-aligned carbon nanotubes by RF-DC plasma chemical vapor deposition

Highly aligned carbon nanotubes (CNTs) were grown under high sheath electric field and gas pressure conditions by the radio frequency (RF) plasma-enhanced direct current (DC) plasma chemical vapor deposition (CVD) method due to a stabilized DC discharge. The uniform growth of highly aligned multi-walled CNTs was achieved over the entire surface area of a 50 × 50 mm² iron foil. The growth of multi-walled CNTs on a 75 × 75 mm² iron foil was also confirmed.     

Synthesis of multi-walled carbon nanotubes by microwave plasma-enhanced chemical vapor deposition

Microwave plasma-enhanced chemical vapor deposition (MW-PECVD) has been employed to synthesize carbon nanostructures by using Fe (or Co, Ni)/γ-Al₂O₃ as catalysts and a mixture of benzene, hydrogen, and argon as precursors. By regulating the types of catalyst, the microwave incident power, the ratio and flux of the precursors, many morphologies such as ordinary geometric, helix-shaped, and planar spiral carbon nanotubes with aspect ratios of 100–1000 have been observed. Furthermore, two novel nanostructures, which are probably the missing link between onion-like carbon particles and nanotubes, have also been obtained. The striking feature of this new approach is the low synthesis temperature (<520°C) due to the non-equilibrium characteristic of microwave plasma operated at low pressure, which is crucial for some fascinating applications.     

A vapor-liquid-solid model for chemical vapor deposition growth of carbon nanotubes

Although carbon nanotubes (CNTs) with a variety of morphologies have been successfully synthesized, there is no clear physical picture of the growth process. Correspondingly, the growth mechanism is still not clear up to now. Here we suggest a VLS model for the growth process of CNTs, which involves a liquid or liquid-like state catalyst. The basic idea is that, due to the high thermal conductivity and nanometer size of the catalyst and the fast diffusion of carbon atoms in it, both the temperature and the carbon atom distribution across it are uniform. The supersaturation level can be expressed as a function of the carbon concentration and temperature, which determines the nucleation dynamics and growth kinetics. Based on this model, the growth rate equation was obtained to describe the growth kinetics of carbon nanotubes, which shows good accordance with the experimental results.     

Catalytic chemical vapor deposition of single-wall carbon nanotubes at low temperatures

We report surface-bound growth of single-wall carbon nanotubes (SWNTs) at temperatures as low as 350 degrees C by catalytic chemical vapor deposition from undiluted C2H2. NH3 or H2 exposure critically facilitates the nanostructuring and activation of sub-nanometer Fe and Al/Fe/Al multilayer catalyst films prior to growth, enabling the SWNT nucleation at lower temperatures. We suggest that carbon nanotube growth is governed by the catalyst surface without the necessity of catalyst liquefaction.     

Role of carbon atoms in plasma-enhanced chemical vapor deposition for carbon nanotubes synthesis

The role of carbon atoms in a dc plasma-enhanced chemical vapor deposition for carbon nanotubes (CNTs) synthesis was investigated. It was observed that at 1.33 kPa pressure of CH₄ gas in plasma, a high value of the ratio between the intensities of the graphite peak (G peak) and the disorder peak (D peak) in the Raman spectrum corresponds to the maximum value of the excited C number density in the vicinity of the Si substrate. It was found that a CH₄ gas pressure higher than 1.33 kPa leads to an increase of the relative density of the C₂, C₃ molecules and the clusters, and to a decrease of the C excited atom number density in plasma. The presence of a high amount of sp²-graphite in the composition of CNTs observed in Raman spectrum was also confirmed by the measurement of the IR-active G peak at 1584 cm^- 1 in the transmission spectrum.     

热化学气相沉积法在硅纳米丝上合成碳纳米管

利用热化学气相沉积法在负载不同厚度催化剂的硅纳米丝(SiNW)表面生长碳纳米管(CNTs),探讨了生长条件对所合成SiNW-CNT的结构和场发射特性的影响.这种类似树状的三维结构具有较高碳纳米管表面密度及降低的电场筛除效应等潜在优势.使用拉曼光谱( Raman)、电子显微镜(SEM)、透射电子显微镜(TEM)、能量扩散分光仪(EDS)分析了碳纳米管的结构性质,并在高真空下施加电场测得碳纳米管的场发射特性.结果表明:随硅纳米丝上负载催化剂镍膜厚度的变化,所合成碳纳米管的表面特性、结晶结构及功函数改变,导致电子发射难易程度的改变,进一步影响碳纳米管的场发射特性.     

Synthesis of sulfur-doped carbon nanotubes from sulfur powder using chemical vapor deposition

Sulfur-doped carbon nanotubes (SCNT) with high sulfur contents have been prepared using chemical vapor deposition (CVD) from sulfur powder, acetylene gas and Fe/CaCO₃ (as catalyst). In this regard, various growth's temperatures were examined to investigate its effects on the structure and the sulfur content of prepared SCNT. The best condition was obtained at 700°C and using 4 g of sulfur powder. The product was characterized using FE-SEM and EDS, which showed rode-like SCNT with about 40 nm diameter and 10.75% sulfur content. Moreover, TEM, Raman and XPS analyses were employed to obtain more details related to the product. The XPS results confirmed the presence of sulfur atoms, which covalently incorporated in the carbon framework. Finally, the catalytic ability of the product in oxygen evolution reaction was examined and the results showed high stability and low oxygen production rate for this product.     

定向碳纳米管的化学气相沉积制备法

报道了一种简便有效的合成定向碳纳米管 (CNTs)的化学气相沉积 (CVD)制备方法。以铁为催化剂 ,乙炔为碳源 ,采用单一反应炉 ,直接在石英基底上沉积催化剂颗粒薄膜 ,成功合成了定向性好、管径均匀的高质量大密度的碳纳米管     

In situ synthesis of ceria decorated carbon nanotubes by chemical vapor deposition

Ceria decorated carbon nanotubes (CNTs) were in-situ synthesized by chemical vapor deposition using a Ni/Ce/Cu catalyst. Ceria nanoparticles, with a diameter of about 3-8 nm, were highly dispersed on the CNTs, and it is believed that they are formed at the same time as the CNTs.     

Structure control of carbon nanotubes using radio-frequency plasma enhanced chemical vapor deposition

Carbon nanotube structures such as tube diameter, growth site, and formation density are controlled using radio-frequency (RF, 13.56 MHz) plasma enhanced chemical vapor deposition (RF-PECVD) method. We have produced uniformly well-aligned multi-walled carbon nanotubes (MWNTs) grown over the large scale area and linearly arrayed MWNTs grown in a selected area without any highly-sophisticated patterning process. In our RF-PECVD experiment, furthermore, individually grown single-walled carbon nanotubes (SWNTs) or their thin bundles are synthesized for the first time within the scope of the PECVD methods. These results indicate that PECVD method provides the high potential for the further development of nano-technology.     

Structure determinations of double-wall carbon nanotubes grown by catalytic chemical vapor deposition

We report an application of nanoarea electron diffraction for structure determination of double-wall carbon nanotubes (DWNT) grown by catalytic chemical vapor deposition. The structures of 30 tubes were determined from experimental diffraction patterns. Among these tubes, the inner and outer wall structure of 18 tubes was precisely determined by comparison with kinematic electron diffraction simulations. For the structure of the DWNTs, our experiment revealed a mixture of semiconducting-metallic (S-M), S-S and M-M tubes. The spacing between the two walls ranges from 0.335 nm to 0.384 nm. Most DWNTs are incommensurate and chiral.     

Carbon dioxide as a carbon source for synthesis of carbon nanotubes by chemical vapor deposition

Carbon dioxide was successfully used as carbon source in the synthesis of carbon nanotubes (CNTs) by chemical vapor deposition (CVD) over Fe/CaO catalyst. The product was evaluated using both transmission electron microscopy (TEM) and Raman spectroscopy. Crooked and branching structures of multi-walled carbon nanotubes (MCNTs) with diameters of around 50 nm were observed on the TEM micrographs. Raman spectrum results show that the nanotubes have small defects, which is in agreement with the results of TEM. The influence of reaction variable such as furnace temperature and types of support media was also studied and the reaction mechanism was then discussed in this paper.