Super-aligned Carbon Nanotube Films Research Articles

Formation of free-standing carbon nanotube array on super-aligned carbon nanotube film and its field emission properties

Flexible and free-standing well-aligned carbon nanotube arrays have been synthesized on super-aligned carbon nanotube films. The combined structure of the carbon nanotube array and carbon nanotube film was formed during chemical vapor deposition on a quartz substrate which had previously been covered with a super-aligned carbon nanotube film. It was found that the growing carbon nanotube array could support up the super-aligned carbon nanotube film entirely, and the top of the array became densely entangled with the super-aligned carbon nanotube film. The carbon nanotube array with the super-aligned carbon nanotube film could be easily peeled off from the quartz substrate as a whole, giving a flexible and free-standing structure with good mechanical properties. The bottom of the array was also exposed after being peeled off and was used as a field emitter. The combined structure of the carbon nanotube array with the carbon nanotube film allowed adsorbent-free field emission by passing a heating current through it. Furthermore, due to the fast thermal response of the structure and the long time needed for re-adsorption of adsorbates in vacuum, it was found that pulsed heating with a 10% duty ratio was sufficient for adsorbent-free field emission. The heating power necessary to sustain the adsorbent-free state can be lowered in this way. Open image in new window

Cross‐Stacked Superaligned Carbon Nanotube Films for Transparent and Stretchable Conductors

AbstractTransparent and stretchable conductors are essential components in many stretchable electronics. However, it is still a challenge to make this kind of conductor easily and cost‐effectively. Here, a way to utilize cross‐stacked superaligned carbon nanotube films to make transparent and stretchable conductors is reported. The as‐produced cross‐stacked films are isotropic in electrical conductivity, but anisotropic in mechanical properties, because of their microscale cross structures. Along some directions, the films can sustain a high strain, of more than 35%, which is helpful for applications as stretchable conductors. These cross‐stacked films can be further made into composite films with polyvinyl alcohol by a dip‐coating method, and with polydimethylsiloxane by an embedding method. The former composite films have similar isotropic electrical and anisotropic mechanical properties to SACNT films, but much larger capability in terms of tensile load. The latter composite films possess quite highly stretchable and reversible electrical behaviors, which can be used in stretchable touch panels, solar cells, strain sensors, and implanted conductors.

A polarized infrared thermal detector made from super-aligned multiwalled carbonnanotube films

Carbon nanotube (CNT) films, easily drawn from super-aligned CNT arrays with a largearea and a good compatibility with semiconductor technology, have been used as lightsensitive materials for infrared (IR) detection. A bolometric CNT detector madefrom one layer of super-aligned CNT film shows a 15.4% resistance change under10 mW mm − 2 of IR illumination and a fast characteristic response time of 4.4 ms due to its ultra-smallheat capacity per unit area in vacuum at room temperature. Besides the power intensitydetection, the anisotropic property of the super-aligned CNT films makes them idealmaterials to detect the polarization of IR light simultaneously, which provides greatpotential in infrared imaging polarimetry. Theoretical analyses have been carried out toinvestigate the influences of CNT film properties on the responsivity and response time ofthe detector.

A general surface-treatment-free approach to fabrication of alignment layers using a super-aligned carbon nanotube film template

We develop a general approach to the fabrication of films with unidirectional grooves, such as silicon nitride, silicon dioxide and aluminium oxide, in which the surface is not required to be treated. Super-aligned carbon nanotube (SACNT) film may be used as a template and as sacrificial layer, which is subsequently removed by heating in an atmosphere of air. The unidirectional morphology of the SACNT film turns into a desired film, which is found to possess the ability to align liquid crystal molecules. This approach also features high efficiency, low cost and easy scaling-up for mass production.

Highly Sensitive Surface-Enhanced Raman Scattering Substrate Made from Superaligned Carbon Nanotubes

Surface-enhanced Raman scattering (SERS) has attracted wide attention because it can enhance normally weak Raman signal by several orders of magnitude and facilitate the sensitive detection of molecules. Conventional SERS substrates are constructed by placing metal nanoparticles on a planar surface. Here we show that, if the planar surface was substituted by a unique nanoporous surface, the enhancement effect can be dramatically improved. The nanoporous surface can be easily fabricated in batches and at low costs by cross stacking superaligned carbon nanotube films. The as-prepared transparent and freestanding SERS substrate is capable of detecting ambient trinitrotoluene vapor, showing much higher Raman enhancement than ordinary planar substrates because of the extremely large surface area and the unique zero-dimensional at one-dimensional nanostructure. These results not only provide a new approach to ultrasensitive SERS substrates, but also are helpful for improving the fundamental understanding of SERS phenomena.

Flexible, Stretchable, Transparent Conducting Films Made from Superaligned Carbon Nanotubes

AbstractA straightforward roll‐to‐roll process for fabricating flexible and stretchable superaligned carbon nanotube films as transparent conducting films is demonstrated. Practical touch panels assembled by using these carbon nanotube conducting films are superior in flexibility and wearability—and comparable in linearity—to touch panels based on indium tin oxide (ITO) films. After suitable laser trimming and deposition of Ni and Au metal, the carbon nanotube film possesses excellent performance with two typical values of sheet resistances and transmittances (208 Ω □−1, 90% and 24 Ω □−1, 83.4%), which are comparable to ITO films and better than the present carbon nanotube conducting films in literature. The results provide a route to produce transparent conducting films more easily, effectively, and cheaply, an important step for realizing industrial‐scale applications of carbon nanotubes for transparent conducting films.

Super-aligned carbon nanotube films as aligning layers and transparent electrodes for liquid crystal displays

Super-aligned carbon nanotube (CNT) film is a transparent conductive film composed of numerous parallel CNTs connected to each other by the van der Waals force. We have found that such films, attached to glass, can readily align liquid crystal molecules. A prototype liquid crystal display (LCD) using the film as the aligning layer has been fabricated. The on–off ratio of the as-prepared display cell is 85 when 24V is the applied voltage. Because of its high transparency, the film can simultaneously be used as a transparent electrode material, in place of expensive indium tin oxide. The resistance of the film makes it a suitable built-in heating layer, extending the working temperature range of LCDs.

Periodically striped films produced from super-aligned carbon nanotube arrays

We report a novel way to draw films from super-aligned carbon nanotube arrays at largedrawing angles. The obtained super-aligned carbon nanotube films have a periodicallystriped configuration with alternating thinner and thicker film sections, and the width ofthe stripes is equal to the height of the original arrays. Compared with ordinary uniformfilms, the striped films provide a better platform for understanding the mechanism ofspinning films from arrays because carbon nanotube junctions are easily observed andidentified at the boundary of the stripes. Further studies show that the carbon nanotubejunctions are bottleneck positions for thermal conduction and mechanical strength of thefilm, but do not limit its electrical conduction. These films can be utilized as striped andhigh-degree polarized light emission sources. Our results will be valuable for newapplications and future large-scale production of tunable super-aligned carbon nanotubefilms.

Superaligned Carbon Nanotube Grid for High Resolution Transmission Electron Microscopy of Nanomaterials

Nano is one of the hottest topics in current science and technology. Characterizations of nanomaterials by high resolution transmission electron microscopy (TEM) are becoming indispensable today. To gain better performance of TEM, people are expecting a novel TEM grid of which the supporting film should be highly conductive, ultrathin but robust, and preferably nanoholey. Here we report a method of mass producing such a kind of carbon nanotube TEM grids. The supporting films are made by cross stacking ultrathin superaligned carbon nanotube films, resulting in a large number of nanosized holes and numerous effective edges. Together with the robustness, good conductivity, and strong adsorbability inherited from carbon nanotubes, these TEM grids show much better performance than conventional amorphous carbon grids.