Rate-Limiting Processes in the Formation of Single-Wall Carbon Nanotubes: Pointing the Way to the Nanotube Formation Mechanism

Single-walled carbon nanotubes synthesized by laser ablation from coal for field-effect transistors

Single-walled carbon nanotubes (SWCNTs) have been attracting extensive attention due to their excellent properties. We have developed a strategy of using coal to synthesize SWCNTs for high performance field-effect transistors (FETs). The high-quality SWCNTs were synthesized by laser ablation using only coal as the carbon source and Co-Ni as the catalyst. We show that coal is a carbon source superior to graphite with higher yield and better selectivity toward SWCNTs with smaller diameters. Without any pre-purification, the as-prepared SWCNTs were directly sorted based on their conductivity and diameter using either aqueous two-phase extraction or organic phase extraction with PCz (poly[9-(1-octylonoyl)-9H-carbazole-2,7-diyl]). The semiconducting SWCNTs sorted by one-step PCz extraction were used to fabricate thin film FETs. The transformation of coal into FETs (and further integrated circuits) demonstrates an efficient way of utilizing natural resources and a marvelous example in green carbon technology. Considering its short steps and high feasibility, it presents great potential in future practical applications not limited to electronics.

Carbon nanotube catalysts: recent advances in synthesis, characterization and applications

Carbon nanotubes are promising materials for various applications.

Spatial recognition of defects and tube type in carbon nanotube field effect transistors using electrostatic force microscopy

The exceedingly high current capacity of single wall carbon nanotubes (SWCNTs) and the high currents that SWCNT thin films can sustain are driving significant efforts to fabricate high quality horizontally aligned SWCNTs. Dielectrophoresis is being increasingly used to prepare aligned nanotubes. However, the aligned nanotubes are generally of low quality since the processing involved can introduce defects. In addition, in arrays of tubes, tube-tube contact resistance can be high. Electrostatic force microscopy is a technique similar to atomic force microscopy, but in this case a bias voltage between the conductive tip and sample enables one to probe the long range electrostatic force. In this study we confirm that the technique can be successfully used to spatially determine defects, crossover points between tubes and nanotube electronic type.

FORMATION OF CARBON NANOTUBES ON CARBON PAPER AND STAINLESS STEEL SCREEN BY OHMICALLY HEATING CATALYTIC SITES

A newly designed gas phase thermal decomposition reactor, ohmically heating the catalytic sites, has been used to synthesize multiwall carbon nanotubes (MWCNTs) on carbon paper and stainless steel screen. Co-Ni catalyst particles were dispersed by a silane intermediate layer adsorbed onto the carbon fibers or the stainless steel threads of the supports. MWCNTs were obtained on both substrates by a tip grown mechanism. They are about 20 μm in length and 15–50 nm in diameter. A methanol pretreatment of the carbon fibers significantly increased the density of the tubes on the carbon paper, but the same treatment had a negative effect on stainless steel. The MWCNTs, which adhere firmly to the carbon paper and the stainless steel screen, may find applications as electrodes in fuel cells, sensors and in photonics.

Growth of few-wall carbon nanotubes with narrow diameter distribution over Fe-Mo-MgO catalyst by methane/acetylene catalytic decomposition

Few-wall carbon nanotubes were synthesized by methane/acetylene decomposition over bimetallic Fe-Mo catalyst with MgO (1:8:40) support at the temperature of 900°C. No calcinations and reduction pretreatments were applied to the catalytic powder. The transmission electron microscopy investigation showed that the synthesized carbon nanotubes [CNTs] have high purity and narrow diameter distribution. Raman spectrum showed that the ratio of G to D band line intensities of IG/ID is approximately 10, and the peaks in the low frequency range were attributed to the radial breathing mode corresponding to the nanotubes of small diameters. Thermogravimetric analysis data indicated no amorphous carbon phases. Experiments conducted at higher gas pressures showed the increase of CNT yield up to 83%. Mössbauer spectroscopy, magnetization measurements, X-ray diffraction, high-resolution transmission electron microscopy, and electron diffraction were employed to evaluate the nature of catalyst particles.

Emprego de subprodutos da produção de piches de petróleo na síntese de nanoesferas de carbono

Nanoesferas de carbono foram produzidas a partir de resíduos de petróleo, obtidos da produção de piches pela destilação de óleos decantados, pela técnica de deposição química de vapor a 1200 °C, sem catalisadores, em um processo contínuo. Três resíduos foram selecionados de forma a representar a faixa de propriedades tipicamente encontradas para este material. Nitrogênio e argônio foram empregados como gases de arraste. As nanoesferas obtidas apresentaram propriedades semelhantes para os três resíduos diferentes, sendo a influência do precursor menos significativa que a do gás de arraste empregado. Os rendimentos obtidos, na faixa de 40-50%, e a baixa sensibilidade do processo à composição do precursor indicam que o processo é adequado à utilização industrial.

Novel catalysts, room temperature, and the importance of oxygen for the synthesis of single-walled carbon nanotubes

In this letter, we show for the first time the use of metal oxides as catalysts in the synthesis of single-walled carbon nanotubes (SWCNTs) using laser ablation. Further, SWCNTs have been synthesized at low temperature (down to room temperature), where their nucleation cannot be explained via fullerene nucleation. The data point to a nucleation mechanism previously not identified, that places a stable oxidized ring as the root cause for the growth of SWCNTs.

Comparison of analytical techniques for purity evaluation of single-walled carbon nanotubes

We compare popular analytical techniques, including scanning and transmission electron microscopy (SEM and TEM), thermogravimetric analysis (TGA), and Raman and near-infrared (NIR) spectroscopy, for the evaluation of the purity of bulk quantities of single-walled carbon nanotubes (SWNTs). Despite their importance as imaging techniques, SEM and TEM are not capable of quantitatively evaluating the purity of typical inhomogeneous bulk SWNT samples because the image frame visualizes less than 1 pg of SWNT material; furthermore, there is no published algorithm to convert such images into numerical data. The TGA technique is capable of measuring the amount of metal catalyst in an SWNT sample, but does not provide an unambiguous separation between the content of SWNTs and carbonaceous impurities. We discuss the utilization of solution-phase near-infrared spectroscopy and solution-phase Raman spectroscopy to quantitatively compare arbitrary samples of bulk SWNT materials of different purities. The primary goal of this paper is to provide the chemical community with a realistic evaluation of current analytical tools for the purity evaluation of a bulk sample of SWNTs. The secondary goal is to draw attention to the growing crisis in the SWNT industry as a result of the lack of quality control and the misleading advertising by suppliers of this material.