Multiwalled carbon nanotube (CNT) arrays were grown by catalytic thermal decomposition of acetylene, over Fe-catalyst deposited on Si-wafer in the temperature range 700-750 °C. The growth parameters were optimized to obtain dense arrays of multiwalled CNTs of uniform diameter. The vertical cross-section of the grown nanotube arrays reveals a quasi-vertical alignment of the nanotubes. The effect of varying the thickness of the catalyst layer and the effect of increasing the growth duration on the morphology and distribution of the grown nanotubes were studied. A scotch-tape test to check the strength of adhesion of the grown CNTs to the Si-substrate surface reveals a strong adhesion between the grown nanotubes and the substrate surface. Transmission electron microscopy analysis of the grown CNTs shows that the grown CNTs are multiwalled nanotubes with a bamboo structure, and follow the base-growth mechanism. 相似文献
We report a detailed longitudinal and depth profiles of multi-wall carbon nanotubes (CNTs) arrays synthesized using xylene and ferrocene in a floating catalyst reactor. Point to point analyses of the CNTs grown in a “growth window” with CNTs arrays longer than 0.5 mm were performed using optical microscopy, Raman spectroscopy, FESEM, high-resolution TGA/DTA, and TEM techniques. The heights of the CNTs arrays show a maximum at a mid point of the growth window, while a reverse trend of minimum is observed for iron-to-CNTs atomic ratios. The ratio of amorphous carbon to CNTs sharply increases along the growth window and from the bottom to top of CNTs arrays. The CNTs diameter also increases along the growth window, due to deposition of the amorphous carbon, which can be almost removed by temperature programmed oxidation up to around 500 °C. A base growth mechanism, the variations of catalyst content, residence time and temperature profile along the growth window, the adsorption and decomposition of polycyclic aromatic hydrocarbons to amorphous carbon, and a limited diffusion of hydrocarbon species through the arrays covered by excessive amorphous carbon may explain the results. 相似文献
Previous energetic considerations have led to the belief that carbon nanotubes (CNTs) of 4 A in diameter are the smallest stable CNTs. Using high-resolution transmission electron microscopy, we find that a stable 3 A CNT can be grown inside a multiwalled carbon nanotube. Density functional calculations indicate that the 3 A CNT is the armchair CNT(2,2) with a radial breathing mode at 787 cm(-1). Each end can be capped by half of a C12 cage (hexagonal prism) containing tetragons. 相似文献
We report on the results of experimental study of an array of vertically aligned carbon nanotubes (VA CNTs) by scanning tunnel microscopy (STM). It is shown that upon the application of an external electric field to the STM probe/VA CNT system, individual VA CNTs are combined into bundles whose diameter depends on the radius of the tip of the STM probe. The memristor effect in VA CNTs is detected. For the VA CNT array under investigation, the resistivity ratio in the low- and high-resistance states at a voltage of 180 mV is 28. The results can be used in the development of structures and technological processes for designing nanoelectronics devices based on VA CNT arrays, including elements of ultrahigh-access memory cells for vacuum microelectronics devices. 相似文献
The current work reports the effect of multi walled carbon nanotubes and single walled carbon nanotubes dispersion on morphological, structural and thermal degradation of electrospun poly(vinyl alcohol) (PVA)/carbon nanotubes (CNTs) dispersed in sodium dodecyl sulfate (SDS) (PVA/CNTs–SDS) composites nanofibers. (PVA/CNTs–SDS) nanocomposites fibers were elaborated using the traditional electrospinning process to disperse and align CNTs into the fibers, especially for low CNTs loading fraction: 0.3 and 0.7 wt%. The morphology of the electrospun fibers was studied using the scanning electronic microscopy. The average diameter of the fibers changes significantly after the incorporation of the CNTs in the PVA. Furthermore, Fourier transform infrared spectroscopy elucidated the effect of CNTs on the crystallization of the PVA which was confirmed by X-ray diffraction analysis. Thermogravimetric analysis showed that the thermal stability of the composite fibers depends on the loading fraction and on the type of carbon nanotubes. 相似文献
Plasma treatments are established methods to functionalise carbon nanotubes (CNTs) and modify their surface structure. This paper presents a mild glow‐discharge plasma treatment of aligned arrays of multi‐walled carbon nanotubes employing sulfur hexafluoride (SF6), ammonia (NH3), and their mixtures as process gases. For the latter, sulfur was detected at the tip and sidewalls of the nanotubes via energy‐dispersive X‐ray spectroscopy, while electron microscopy served as method to verify the structural integrity of the CNTs after the plasma treatment. This approach provides the basis for an easy and quick alternative to existing sulfur functionalisation methods of MWCNTs. Furthermore, the proposed method can conveniently be applied to carbon nanotube arrays on substrate while preserving their structure and alignment.
SEM‐EDX map of SF6/NH3 plasma‐treated multi‐walled carbon nanotubes on substrate. Green, yellow and red correspond to silicon, carbon and sulfur signals, respectively. 相似文献
In this paper, we have studied field emission properties of highly dense arrays of multi-walled carbon nanotubes (CNTs) used
as cathodes in diode-type field emission devices with a phosphor screen. For the high-density CNT emitters it is demonstrated
that the emission sites are located on the CNT-cathode edges, which is direct experimental evidence of the ‘edge effect’.
The results of computer simulations (using ‘ANSYS Electromagnetic’ software) are presented to confirm the experimental data
and to analyze the effect of patterning on the electric field distribution for high-density CNT arrays. It is shown that selective-area
removal of nanotubes in the arrays leads to the formation of additional edges characterized by the high field enhancement
factor and enhanced emission from the CNT cathodes. In addition, scanning probe microscopy techniques are employed to examine
surface properties of the high-density CNT arrays. For CNT arrays of ‘short’ nanotubes, the work function distribution over
the sample surface is detected using a scanning Kelvin microscopy method. 相似文献
The effect of gas pressure on the structure of carbon nanotubes (CNTs) has been systematically investigated in the chemical
vapor deposition process. The yield of CNTs (defined as the weight ratio of CNTs vs. catalyst) increases significantly with
the gas pressure, reaches 600% at 600 Torr, then decreases with further increase of gas pressure. At low reacting gas pressure
the CNTs have completely hollow cores, whereas at high pressure the CNTs have a bamboo structure. The density of the compartments
in the bamboo-structured CNTs increases dramatically with the increase of the gas pressure. This result shows that the structure
and yield of carbon nanotubes are strongly affected by the growth gas pressure.
Received: 10 May 2001 / Accepted: 10 May 2001 / Published online: 20 June 2001 相似文献