Synthesis of carbon nanofiber films and nanofiber composite coatings by laser-assisted catalytic chemical vapor deposition

Uniform carbon nanofiber films and nanofiber composite coatings were synthesized from ethylene on nickel coated alumina substrates by laser-assisted catalytic chemical vapor deposition. Laser annealing of a 50 nm thick nickel film produced the catalytic nanoparticles. Thermal decomposition of ethylene over nickel nanoparticles was initiated and maintained by an argon ion laser operated at 488 nm. The films were examined by scanning electron microscopy and by transmission electron microscopy. Overall film uniformity and structure were assessed using micro-Raman spectroscopy. Film quality was related to the experimental parameters such as incident laser power density and irradiation time. For long irradiation times, carbon can be deposited by a thermal process rather than by a catalytic reaction directly over the nanofiber films to form carbon nanocomposite coatings. The process parameters leading to high quality nanofiber films free of amorphous carbon by-products as well as those leading to nanofiber composite coatings are presented.     

Growth and microstructures of carbon nanotube films prepared by microwave plasma enhanced chemical vapor deposition process

Well-aligned carbon nanotubes (CNTs) were grown on iron coated silicon substrates by microwave plasma enhanced chemical vapor deposition. Effect of plasma composition on the growth and microstructures of CNTs were investigated by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and optical emission spectroscopy. Morphology and microstructure of nanotubes were found to be strongly dependent on the plasma composition. Aligned bamboo-shaped nanotubes consisting of regular cone shaped compartments were observed for C₂H₂/NH₃/N₂ and C₂H₂/NH₃/H₂ gas mixtures. Randomly oriented or no nanotubes growth were observed in C₂H₂/H₂ and C₂H₂/N₂ gas mixtures respectively. CNTs grown in nitrogen rich plasma had more frequent short compartments while compartment length increased with decreasing nitrogen concentration in the plasma. Raman spectroscopy of CNTs samples revealed that CNTs prepared in nitrogen rich plasma had higher degree of disorder than those in low nitrogen or nitrogen free plasma. In-situ optical emission spectroscopy investigations showed that CN and H radicals play very important role in both the growth and microstructure of CNTs. Microstructure of CNTs has been correlated as a function of CN radical concentration in the plasma. It is suggested that presence of nitrogen in the plasma enhances the bulk diffusion of carbon through the iron catalyst particles which causes compartment formation. Based on our experimental observations, growth model of nanotubes under different plasma composition has been suggested using base growth mechanism.     

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。     

Electrical properties/Doping efficiency of doped microcrystalline silicon layers prepared by hot-wire chemical vapor deposition

Microcrystalline silicon (μc-Si) doped films were prepared by hot-wire chemical vapor deposition (HWCVD) to investigate the doping efficiency. The incorporation probability of different dopant atoms into the solid-phase is always increasing with the doping gas concentrations, but very different for the doping gases used: trimethylboron (TMB), boron trifluoride (BF₃) and phosphine (PH₃). At the same doping gas concentration in the process gas the incorporation of phosphorus atoms into the solid μc-Si phase is much larger than that of boron atoms with respect to the dissociation probability of the doping gases. The electron and hole concentrations, estimated from Hall measurements, are directly related to the solid phase concentration of the doping atoms and independent of the type of dopant and the doping gas used. This results in an equal doping efficiency of about 20 % for the incorporated B and P atoms in doped HWCVD μc-Si films. For the dopant atom concentration regime investigated the doping efficiency of B atoms is in good agreement with corresponding PECVD doping efficiencies however, the doping efficiency of P atoms is considerably lower for our n-doped films.     

Synthesis of carbon nanowalls by hot-wire chemical vapor deposition

Carbon nanowall (CNW) is a carbon nano-material which has a wall structure that stood on substrates. CNWs can be synthesized by hot-wire chemical vapor deposition (HWCVD) using methane without hydrogen dilution. The synthesis of CNWs by HWCVD is discussed along with reviewing the experimental results. The growth of CNWs is affected by hydrogen dilution ratio and substrate surface temperature. Based on these results, it is suggested that hydrogen radical density and substrate surface temperature are the important parameters for the synthesis of CNWs. The growth process of CNWs is also discussed.     

Synthesis and characterization of Y-shaped carbon fibers by chemical vapor deposition

In this work, Y-shaped carbon fibers with high purity were successfully synthesized by CVD using copper tartrate as a catalyst precursor at low reaction temperature, 279 °C. A model has been proposed for interpreting the mechanism of the Y-shaped carbon fibers growth. It is suggested that the introduction of hydrogen is the key factor to the formation of three carbon fibers growth faces on every the agglomeration of copper monocrystalline catalyst particles and lead to the formation of Y-shaped carbon fibers subsequently. The Y-shaped carbon fibers were characterized by field emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction.     

Fabrication of PTFE thin films by dual catalytic chemical vapor deposition method

Dependence of catalyzing materials on deposition of polytetrafluoroethylene (PTFE = ”Teflon” in commercial) films by catalytic chemical vapor deposition (Cat-CVD) method is investigated. It has been clarified that Ni-containing catalyzers has a catalyzing effect that can decompose hexafluoropropylene-oxide (HFPO) to form PTFE films. A novel method named Dual Cat-CVD is also proposed. In the method, carbonized and fluorinated surface of Ni-containing catalyzer is removed and refreshed using atomic hydrogen generated by additionally introduced tungsten (W) catalyzer in the same chamber. This Dual Cat-CVD method enables to recover the deposition rate of PTFE films drastically.     

爆炸辅助气相沉积法制备炭纳米线的研究

根据爆炸辅助气相沉积法生长碳纳米管的机理,设计了两种制备炭纳米线的方案:(1)使用低活性铁-镍二元金属催化剂;(2)对钴催化剂作用下碳纳米管的生长实施冷冻。透射电子显微镜显示这两种方法制备的炭纳米线均为纳米颗粒组装而成,具有非常粗糙的表面。其中,使用铁-镍二元催化剂所制炭纳米线直径分布不均匀,黏结情况严重;而在冷冻钴催化剂作用下炭纳米管生长过程所得的炭纳米线直径分布比较均匀,黏结情况也大为减少。这两种纳米线的差别与金属催化剂的活性有关。光催化降解亚甲基蓝实验表明:冷冻碳纳米管生长所得炭纳米线具有良好的催化辅助功能,可以提高ZnS纳米晶的光催化活性。     

Magnetic behavior of cobalt oxide films prepared by pulsed liquid injection chemical vapor deposition from a metal-organic precursor

Thin films of cobalt oxide were prepared by the pulsed liquid injection chemical vapor deposition technique from metal-organic precursor. By using a β-diketonate complex of cobalt, namely cobalt (II) acetylacetonate (Co(acac)₂) as the precursor, oxygen as the reactant and argon as the carrier gas, cobalt oxide films 100 nm in thick were deposited onto Si (100) substrates at 650 °C in about 40 min. According to the characterization by X-ray diffraction and atomic force microscopy, smooth and polycrystalline films, consisting exclusively of the Co₃O₄ phase, were deposited. Magnetic properties, such as saturation magnetization, the remanence, the coercivity, the squareness ratio and the switching field distribution, were extracted from the hysteresis loop. Cobalt oxide films with coercivities of 6.61 mT, squareness ratio of 0.2607 and saturation magnetization of 12.17 nA m², corresponding to a soft magnetic material, were achieved.     

直流热阴极CVD金刚石薄膜生长特性研究

为了获得高质量的金刚石薄膜,采用直流热阴极化学气相沉积系统分别在不同基片温度和不同碳源气体含量条件下生长金刚石薄膜,利用Raman光谱、SEM和XRD检测方法研究了基片温度和碳源气体含量对金刚石薄膜生长特性的影响.结果表明,金刚石薄膜与基片Mo之间有Mo2C的过渡层存在;1000℃的温度能够促进金刚石晶体的生长,抑制其他碳杂质的形成,CH4体积分数为2%适于快速生长高纯度的金刚石薄膜.     

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.     

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     

Synthesis and characterization of carbon spheres prepared by chemical vapour deposition

Carbon spheres, with uniform diameters of about 1 μm, have been achieved via Chemical vapour deposition (CVD). The fabricated materials have been fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray analysis (EDX). The results show that the spheres are 95% carbon. The formation mechanism of carbon spheres has also been discussed.     

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.     

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.     

Polymer layers by initiated chemical vapor deposition for thin film gas barrier encapsulation

A combination of SiN_x and polymer layers, in our case poly(glycidyl methacrylate) (PGMA) is very suitable as a permeation barrier layer on sensitive electronic devices. Our experiments thus far concentrate on increasing the stability and deposition rate of the polymer layers. To reach the thermal stability needed for the deposition of SiN_x on PGMA by HWCVD, the PGMA chain length must be large. PGMA with a very high molecular weight (M_W) (78,000 Da, ~ 548 monomers) was deposited at a high deposition rate (> 60 nm/min). To mimic the reactive atomic H ambient during SiN_x deposition conditions during HWCVD, the polymer layers were exposed to an atomic hydrogen environment for 0 to 550 s. Surprisingly, the most important factor for stability under these conditions was the filament temperature which was used during PGMA deposition, rather than the expected parameters such as M_W or surface roughness. Using lower filament temperatures for PGMA deposition, the layers were much more stable in atomic H ambient.     

Optimization of processing parameters of the chemical vapor deposition process for synthesizing high-quality single-walled carbon nanotube fluff and roving

The use of the Taguchi method to optimize the processing parameters for the synthesis of high-quality single-walled carbon nanotubes (SWCNTs) in a vertical chemical vapor deposition reactor was demonstrated. An investigation containing 18 experiments featuring different parameters and levels was performed. SWCNTs with a low intensity D-band to G-band ratio of 0.027 of a Raman spectrum were obtained when the optimal processing conditions were adopted. The quantitative contribution of the processing parameters can be calculated using the analysis of variance. According to the analysis, the reactor temperature and the evaporation temperature of ferrocene significantly affect the graphitization of the synthesized SWCNTs, while the chamber pressure exerts an insignificant effect. The formation of carbon nanotube films with entangled networks during synthesis was recorded using a digital camera, and a synthesis mechanism was proposed. Using the optimal parameters, SWCNT fluff with a diameter of 7.0 cm and SWCNT roving with a diameter of approximately 1.0 cm and a length of over 30.0 cm can be attained. In this work, field-emission scanning electron microscopy and Raman spectroscopy and high-resolution transmission electron microscopy were adopted to examine the morphology and microstructure, respectively.     

Thin-film phases of organic charge-transfer complexes formed by chemical vapor deposition

Thin films of organic charge-transfer salts, (TTF)(TCNQ) and (TTF)(DMDCNQI), are prepared by the chemical vapor deposition method, where TTF is tetrathiafulvalene, TCNQ is tetracyanoquinodimethane, and DMDCNQI is dimethyldicyanoquinonediimine. Depending on the substrate temperatures, we have obtained randomly oriented polycrystalline phases composed of relatively large crystals and microcrystalline thin-film phases, which sometimes contain well-grown nanowires. The latter shows much different conducting properties from the bulk crystals, and particularly the (TTF)(DMDCNQI) film is nearly as conductive as the (TTF)(TCNQ) film in spite of the bulk insulating property coming from the mixed-stack crystal structure.     

Characterizations of gallium-doped ZnO films on glass substrate prepared by atmospheric pressure metal-organic chemical vapor deposition

Ga-doped zinc oxide (ZnO:Ga) films were grown on glass substrate by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD) using diethylzinc and water as reactant gases and triethyl gallium (TEG) as an n-type dopant gas. The structural, electrical and optical properties of ZnO:Ga films obtained at various flow rates of TEG ranging from 1.5 to 10 sccm were investigated. X-ray diffraction patterns and scanning electron microscopy images indicated that Ga-doping plays an important role in forming microstructures in ZnO films. A smooth surface with a predominant orientation of (101) was obtained for the ZnO:Ga film grown at a flow rate of TEG = 7.5 sccm. Moreover, a lowest resistivity of 3.6 × 10^− 4 Ω cm and a highest mobility of 30.4 cm² V^− 1 s^− 1 were presented by the same sample, as evaluated by Hall measurement. Otherwise, as the flow rate of TEG was increased, the average transmittance of ZnO:Ga films increased from 75% to more than 85% in the wavelength range of 400-800 nm, simultaneously with a blue-shift in the absorption edge. The results obtained suggest that low-resistivity and high-transparency ZnO films can be obtained by AP-MOCVD using Ga-doping sufficiently to make the films grow degenerate and effect the Burstein-Moss shift to raise the band-gap energy from 3.26 to 3.71 eV.     

乙炔催化裂解制备碳纳米带及其结构表征

以乙炔（C2H2）为碳源,铁为催化剂,通过化学气相沉积技术在单晶硅衬底上制备了碳纳米带.采用场发射SEM、TEM、激光Raman光谱等先进分析手段对其形态和结构进行了表征.研究发现：碳纳米带是一种准二维材料,厚度约30nm,宽度在几百纳米,长度在100μm量级.碳纳米带的碳层沿着与其生长轴方向一致的（002）晶向排列,碳层的边缘都弯曲折叠成封闭结构.碳纳米带中碳层的排列不很平直,其中存在大量的层错.由此认为碳纳米带可用于能源等领域.