Structure and energetics of carbon nanotube ropes

High-resolution electron microscopy observation and energetic analysis have been performed on ropes formed from single-walled carbon nanotubes. When individual nanotubes are twisted, the nanotube ropes become energetically stable—a configuration that also offers better structural stability. Electron microscopic image simulations of an energetically-stable rope composed of seven single-walled carbon nanotubes have been carried out as well to elaborate the salient features that were observed experimentally.     

化学气相沉积工艺制备绳状纳米碳管的研究

用硝酸铁作催化剂,乙炔作碳源气体,高纯氮气作稀释气体,在750℃下化学气相沉积生长了绳状纳米碳管,用高分辨扫描电镜观察了所得绳状纳米碳管的形貌.纳米碳管的直径为100～200nm,长度为10～20 μm.文中还提出了绳状纳米碳管的生长机理.     

Carbon nanotube films as electron field emitters

Carbon nanotubes have been recognized as one of the most promising electron field emitters currently available. We review the state of the art of current research on the electron field emission properties of carbon nanotube films and present recent results outlining their potential as field emitters as well as illustrating some current concerns in the research field.     

Carbon nanotube yarns

A CNT yarn is a collection of interlocked CNTs which form a long and continuous fiber of macroscopic scale. CNT yarns of more than a kilometer are now available so that they have been drawing ever-growing attention from the scientific community. In principle, CNT yarns can inherit the excellent electrical, mechanical and chemical properties of CNTs provided they are produced perfectly. In this perspective review, the production methods of CNT yarns are extensively investigated and reported in detail. Although CNT yarns have a great potential to revolutionize our future, it can only be possible by improving their essential material properties such as tensile strength and edectrical conductivity.     

Carbon nanotube biogels

There are numerous biomedical devices that rely on efficient electrical communication with living tissue. Advancement of these devices depends on effectively bridging the tissue/electrode interface and is dependent on advances in new materials. We report on the modification of carbon nanotubes with various biomolecules to develop biological based conducting material suitable for bridging this interface. The non-covalent modification of single-wall carbon nanotubes (SWCNT) with three biological molecules (DNA, hyaluronic acid and chitosan) has been achieved. Coherent SWCNT biofilms were produced from the dispersions by drop casting onto glassy carbon electrodes. The SWCNT biofilms underwent hydration upon immersion into electrolyte to form a gel that exhibited considerably lower impedance than the glassy carbon substrate. In addition, incorporation of the neurotrophin NT-3 into these CNT biogels was possible with the controlled release of the NT-3 being influenced by the application of electrical stimulation. Compatibility of the materials prepared with a fibroblast cell line (L-929) was also tested and it was determined that they were non-toxic to the cells under consideration. The soft character of these conducting biogels coupled with their dynamic nature provides an extra dimension in designing interfaces between the hard, digital electronics world and the soft, amorphous world of biological systems.     

Carbon nanotube growth mechanism switches from tip- to base-growth with decreasing catalyst particle size

The growth of carbon nanotubes by a plasma assisted catalytic chemical vapor deposition was investigated using cobalt, nickel and iron catalyst particles of different sizes. For the three catalysts examined, it was shown that the growth mode switches from “tip-growth” for large particles (>>5 nm) to “base-growth” for smaller ones (<5 nm). While single-walled nanotubes and those with few walls (typically <7 walls) grow from their base, larger multi-walled nanotubes are fed with carbon via their tips which support the catalyst particle. A growth scenario involving two different pathways for carbon diffusion is proposed in order to explain the change in growth mode.     

Carbon nanotube cloth as a promising electrode material for flexible aqueous supercapacitors

Journal of Applied Electrochemistry - Electrochemical cyclic recharging of a binder-free flexible carbon material in respect to supercapacitor applications is reported. To provide high enough and...     

Mechanical and NH3 sensing properties of long multi-walled carbon nanotube ropes

Mechanical properties of long multi-walled CNT ropes prepared using the floating catalyst chemical vapour deposition method were tested, obtaining an average tensile strength and Young’s modulus of 210 MPa and 2.2 GPa, respectively. Furthermore, the ropes showed excellent NH₃ detecting sensitivity at both high and low NH₃ concentrations. Increasing the temperature, NH₃ desorbed from the ropes, indicating an exothermal absorption reaction.     

Carbon nanotube wires for high-temperature performance

We developed carbon nanotube wires (CNWs) and monitored in situ their electrical properties at high temperature conditions for the first time. The dominant type of CNTs present in the material and packing density of thereof proved to have a dominant effect on the thermal stability of CNWs. Furthermore, we showed that kinetics of CNW oxidation plays an important role and slow heating rates or prolonged heating times are essential for the proper determination of thermal stability of CNTs. To enhance the stability at high temperatures, we applied SiC coating onto the CNWs, what allowed a 300 °C improvement to the operational window, eventually reaching 700 °C in the long-haul. Correlation of the change in electrical properties with thermogravimetric response showed that the loss of electrical percolation takes place at 100 °C lower temperature than the last observed weight loss in CNTs content. Finally, we demonstrated feasibility of SiC-coated CNWs under high temperature conditions, by creating a heating device out of them. The presence of SiC layer gave rise to a significant improvement to the thermal stability of the CNT heaters, which now offer unprecedented range of operation reaching 700 °C, as compared to 400 °C when uncoated.     

Carbon nanotube networks on different platforms

Carbon nanotube (CNT) networks are an emerging class of material with potential applications that range from biotechnology to sensors. However, the design and fabrication of CNT networks with specific properties necessitates a deep understanding on how a variety of factors affect the performance of these materials. Of particular interest is how the substrate on which the CNT networks are assembled also influences on the applicational aspects of the CNT network. In this review, we overview the variety of substrates reported as CNT networks supports, and the different applications of these networks. Substrates can be varied from rigid to flexible to porous materials. Interestingly, the method of network preparation and the nature of the scaffold have a direct influence on the properties and the potential applications of the final material.     

Carbon nanotube toughened aluminium oxide nanocomposite

This paper describes the mechanical properties of carbon nanotube-reinforced Al₂O₃ nanocomposites fabricated by hot-pressing. The results showed that compared with monolithic Al₂O₃ the fracture toughness, hardness and flexural strength of the nanocomposites were improved by 94%, 13% and 6.4% respectively, at 4 vol.% CNT additions. For 10 vol.% CNT additions, with the exception of the fracture toughness, which was improved by 66%, a decrease in mechanical properties was observed when compared with those for monolithic Al₂O₃. The toughening mechanism is discussed, which is due to the uniform dispersion of CNTs within the matrix, adequate densification, and proper CNT/matrix interfacial connections.     

Carbon nanotube synthesis upon stainless steel meshes

In this paper we report and interpret the effectiveness of different bulk metal catalyst preparations and of various components within reactive gas mixtures for carbon nanotube (CNT) synthesis. The combined catalyst precursor and supporting material is type 304 stainless steel mesh. The steel mesh keenly illustrates the net effect of different pretreatments upon the catalyst because of its resistance to oxidation. These preparative treatments include oxidation, reduction, and their combinations. Finally the utility of the different components within the reactive gas mixture are illustrated by synthesis tests in their individual absence. The effect of catalyst preparation and gas mixture on CNT synthesis is judged on the basis of the relative surface density and morphology of the CNTs (as observed via SEM) and their graphitic structure (as observed via TEM).     

Carbon nanotube growth by rapid thermal processing

A new method for carbon nanotube (CNT) growth by rapid thermal processing (RTP) of amorphous carbon film is reported. This is a two-step method, involving an ion-beam sputtering process followed by an RTP treatment. Amorphous carbon film containing iron was first deposited by ion-beam sputtering. The as-deposited films were then annealed by RTP under an inert environment. High-density multi-wall carbon nanotubes with a length of 1 μm and a diameter of approximately 30 nm were observed on the surface of amorphous carbon film after RTP at 1200°C for 30 s in nitrogen (N₂). Detailed morphology and structure analyses of carbon nanotubes thus obtained using SEM and HR-TEM indicated that the number density and growth rate of the CNT were dependent on the process temperature and ambient gas. The use of RTP provides a straightforward, convenient and cost-effective method to grow carbon nanotubes with controllable length and density.     

Carbon nanotube capacitors arrays using high-k dielectrics

The electrical characteristics and fabrication process of nanocapacitor arrays using metal-high-k dielectric-carbon nanotube-metal layers (MICntM) were studied. MWCNTs arrays were fabricated using an electron beam lithography based lift-off process for catalyst definition and the high-k dielectric layer, hafnium oxide (HfO₂), was deposited using rf magnetron sputtering. The MICntM structures show high capacitance and the compatibility with high-k dielectric material and its deposition processes. MICntM capacitors arrays with sputtered HfO₂ show specific capacitance of 0.62 μF/cm². The leakage current density at 1 V is less than 5 μA/cm². The high aspect ratio of MWCNTs increases the effective electrode area and HfO₂ allows higher permittivity, hence, higher capacitance structures are realized.     

Carbon nanotube reinforced shape memory polyurethane foam

Multiwalled carbon nanotube (MWCNT)/polyurethane (PU) foams have been synthesized from polypropylene glycol and 2,4/2,6-toluene diisocyanate following the one-shot foaming method in the presence of water as the chemical blowing agent. The effects of CNT content on the performances of the foams have been analyzed in terms of reactivity, mechanical and dynamic mechanical properties, and shape memory properties of the foams. It was found that the cream time, rise time, tensile, and compressive strengths at room temperature, glassy and rubbery state moduli, glass-transitional temperature (T _g), and shape fixity and shape recovery increased with the addition and increasing amount of MWCNT.     

Carbon nanotube–carbon nanotube contacts as an alternative towards low resistance horizontal interconnects

We propose to use carbon nanotube (CNT)–CNT contacts instead of CNT–metal contacts as a route towards low resistance CNT horizontal interconnects. We characterize by electrical transport measurements and Kelvin probe force microscopy the contacts present in CNT horizontal interconnects grown by chemical vapor deposition between titanium nitride electrodes.When two CNTs with diameter around 30 nm grow from opposing electrodes and touch each other with their outermost shells, typical contact resistances around 16 kΩ are obtained. The corresponding contact resistivity of about 14 Ω μm² is one order of magnitude smaller than the contact resistivity of a CNT touching the TiN surface with its outermost shell. On the other hand, the contact resistance of a CNT grown from a nickel catalyst particle deposited on a TiN electrode is negligibly small when compared to the above mentioned contact resistances. Our results demonstrate that we are able to grow from opposing electrodes CNTs that touch each other with a corresponding high density (up to 10¹¹ cm⁻²) of CNT–CNT contacts. This may offer an effective solution towards the growth of low resistance CNT horizontal interconnects.