CVD Growth of Carbon Nanotubes and Nanofibers: Big Length and Constant Diameter

Summary: We report mass production of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) with relatively high length and aspect ratio. We synthesized carbon nanomaterials by chemical vapor deposition (CVD) of methane as the feeding gas on Fe/Mo nanoparticles that use alumina-aerogel support. Alumina-aerogel-supported Fe/Mo catalyst was prepared using sol-gel. Drying step performed using rotary evaporation and freeze-drying. CVD was performed using a quartz tube furnace. Samples were analyzed using scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Raman spectroscopy.     

The production of carbon nanotubes from carbon dioxide: challenges and opportunities

Recent advances in the production of carbon nanotubes (CNTs) are reviewed with an emphasis on the use of carbon dioxide (CO2) as a sole source of carbon. Compared to the most widely used carbon precursors such as graphite, methane, acetylene, ethanol, ethylene, and coal-derived hydrocarbons, CO2 is competitively cheaper with relatively high carbon yield content. However, CNT synthesis from CO2 is a newly emerging technology, and hence it needs to be explored further. A theoretical and analytical comparison of the currently existing CNT-CO2 synthesis techniques is given including a review of some of the process parameters (i.e., temperature, pressure, catalyst, etc.) that affect the CO2 reduction rate. Such analysis indicates that there is still a fundamental need to further explore the following aspects so as to realize the full potential of CO2 based CNT technology: (1) the CNT-CO2 synthesis and formation mechanism, (2) catalytic effects of transitional metals and mechanisms, (3) utilization of metallocenes in the CNT-CO2 reactions, (4) applicability of ferrite-organometallic compounds in the CNT-CO2 synthesis reactions, and (5) the effects of process parameters such as temperature, etc.     

Growth of carbon nanotubes on the novel FeCo-Al2O3 catalyst prepared by ultrasonic coprecipitation

FeCo-Al_2O_3 catalyst was prepared by an ultrasonic coprecipitation (UC) method for the growth of carbon nanotubes (CNTs) from catalytic decomposition of methane. Its catalytic performance was compared with that of the FeCo-Al_2O_3 catalyst counterparts prepared by stepwise impregnation (I) and conventional coprecipitation (C) methods, respectively. The structure and properties of the catalysts and the CNTs as produced thereon were investigated by means of XRD, XPS, TEM and N_2 adsorption techniques. It was found that the catalyst prepared by the ultrasonic coprecipitation method was more active, and the yield and purity of the synthesized CNTs were promoted evidently. The XPS results revealed that there were more active components on the surface of the catalyst prepared by the ultrasonic coprecipitation method. On the other hand, N_2 adsorption demonstrated that the catalyst prepared by the ultrasonic coprecipitation method conferred larger specific surface area, which was beneficial to dispersion of active components. TEM images further confirmed its higher dispersion. These factors could be responsible for its higher activity for the growth of CNTs from catalytic decomposition of methane.     

定位生长法制备AFM单壁碳纳米管针尖

采用粘性胶状物作为生长单壁碳纳米管(SWNTs)的催化剂前驱体, 在原子力显微镜下驱动废旧的硅探针粘附该种胶状物,随后进行化学气相沉积(CVD), 实现了SWNTs在硅探针末端的定位生长, 成功地制备出了SWNT针尖. 对SWNTs及SWNT 针尖进行了表征, 并对针尖的稳定成像条件进行了分析. 结果表明, 针尖一般由5-10 nm 的SWNT 管束构成, 伸出长度仅为几百纳米, 受热振动影响较小, 无需后处理即可稳定地成像, 成像分辨率与新的硅探针相当.     

Cathodoluminescence properties of silicon nanocrystallites embedded in silicon oxide thin films

Cathodoluminescence (CL) spectra for the Si nanocrystallites embedded in a matrix of silicon oxide films are measured at room temperature. The CL spectra consist of two principal bands whose peak energies are in a near-infrared (NIR) region (<1.6 eV) and in a blue region (2.6 eV), respectively. The spectral feature of the NIR CL band is similar to the corresponding PL spectra. The strong correlation between the presence of Si nanocrystallites and the formation of the NIR CL band are found as well as the PL spectrum. The peak energy of the blue CL band is slightly lower than that of the luminescence band originating from oxygen vacancies (≡Si–Si≡) in SiO₂. Therefore, the blue CL band is considered to come from Si_n clusters with n3 in the oxide matrix. Under irradiation of electron beams, degradation of the intensity is observed for both the CL bands but the decay characteristics are different.     

巴基管嵌锂电极性能的研究

用化学气相沉积法制备的巴基管作为锂离子电池的负极活性物质可以达到７００ｍＡｈ／ｇ的容量，远超过了石墨嵌锂化合物理论容量。ＣＶＤ巴基管电极经２０次充放电循环后，放电容量保持率为６５．３％，尽管ＣＶＤ巴基管电极初次充放电效率低，但经表面镀铜修饰后，初次充放电效率可提高到５５．９％。     

Laser Induced Damage in CVD Diamond Films

ＬａｓｅｒＩｎｄｕｃｅｄＤａｍａｇｅｉｎＣＶＤＤｉａｍｏｎｄＦｉｌｍｓＱＩＵＨｏｎｇＦＡＮＺｈｅｎｇｘｉｕ（ＳｈａｎｇｈａｉＩｎｓｔｉｔｕｔｅｏｆＯｐｔｉｃｓａｎｄＦｉｎｅＭｅｃｈａｎｉｃｓ，ＣｈｉｎｅｓｅＡｃａｄｅｍｙｏｆＳｃｉｅｎｃｅｓ，Ｐ．Ｏ．...     

Silicon carbonitride by remote microwave plasma CVD from organosilicon precursor: Growth mechanism and structure of resulting Si:C:N films

The remote microwave hydrogen plasma chemical vapor deposition (RP-CVD) from bis(dimethylamino)methylsilane precursor was used for the synthesis of silicon carbonitride (Si:C:N) films. The effect of thermal activation on the RP-CVD process was examined by determining the mass- and the thickness-based film growth rate and film growth yield, at different substrate temperature (T_S). It was found that the mechanism of the process depends on T_S and for low substrate temperature regime, 30 °C ≤ T_S ≤ 100 °C, RP-CVD is limited by desorption of film-forming precursors, whereas for high substrate temperature regime, 100 °C < T_S ≤ 400 °C, RP-CVD is a non-thermally activated and mass-transport limited process. The Si:C:N films were characterized by X-ray photoelectron and Fourier transform infrared spectroscopies, as well as by atomic force microscopy. The increase of T_S enhances crosslinking in the film via the formation of nitridic Si-N and carbidic Si-C bonds. On the basis of the structural data a hypothetical crsosslinking reactions contributing to silicon carbonitride network formation have been proposed.     

Effects of Ni catalyst–substrate interaction on carbon nanotubes growth by CVD

An investigation of the effects of substrate type and various treatments on carbon nanotubes (CNT) growth, using an evaporated Ni thin film as a catalyst, is presented. Barrier layers of SiO₂, Si₃N₄, and TiN on Si were used as substrates. The catalyst-insulating substrate systems have been processed in several gaseous atmospheres (Ar, NH₃ and H₂) and in the temperature range 700–900 °C, in order to obtain the most appropriate morphology, size and density of catalyst particles as seeds for the subsequent CNT growth. On this kind of substrates, the smallest nanoparticles were obtained on SiO₂ layers, in H₂ or NH₃ atmosphere even at 700 °C. However, the best vertically aligned and well-graphitized CNT resulted from the NH₃ annealing process, followed by the CNT deposition at 900 °C in C₂H₂ and H₂.On TiN conducting substrates, the best vertically aligned CNT were deposited using a shorter annealing step and a deposition process at reduced pressure. The samples were characterized by means of scanning electron microscopy (SEM) and Raman spectroscopy analysis.