Photonic Sorting of Aligned, Crystalline Carbon Nanotube Textiles

Abstract

Floating catalyst chemical vapor deposition uniquely generates aligned carbon nanotube (CNT) textiles with individual CNT lengths magnitudes longer than competing processes, though hindered by impurities and intrinsic/extrinsic defects. We present a photonic-based post-process, particularly suited for these textiles, that selectively removes defective CNTs and other carbons not forming a threshold thermal pathway. In this method, a large diameter laser beam rasters across the surface of a partly aligned CNT textile in air, suspended from its ends. This results in brilliant, localized oxidation, where remaining material is an optically transparent film comprised of few-walled CNTs with profound and unique improvement in microstructure alignment and crystallinity. Raman spectroscopy shows substantial D peak suppression while preserving radial breathing modes. This increases the undoped, specific electrical conductivity at least an order of magnitude to beyond that of single-crystal graphite. Cryogenic conductivity measurements indicate intrinsic transport enhancement, opposed to simply removing nonconductive carbons/residual catalyst.

Extreme stretching of high G:D ratio carbon nanotube fibers using super-acid

“…From the as-is state, there is an order of magnitude enhancement where now a significant portion of the specific conductivity distribution is above the specific conductivity of single-crystal graphite (1100 Sm 2 kg ─1 ) and at its maximum reaches 45% higher (1595 Sm 2 kg ─1 ). This de-doped conductivity is comparable to the highest reported floating catalyst derived material that is accompanied by some nondoping post-processing, namely: rollers (1700 Sm 2 kg ─1 [36]), drawing dies (1770 Sm 2 kg ─1 [37]), and lasersorting (1500 Sm 2 kg ─1 [38]). Note that the overnight vacuum baking at 300 °C is intended to remove trapped liquid and physisorbed chemical species for better material stability and repeatability.…”

Catalyst-Mediated Enhancement of Carbon Nanotube Textiles by Laser Irradiation: Nanoparticle Sweating and Bundle Alignment

“…In this paper, we present photonic processing as a fast, scalable method to enhance a CNT textile's microstructure, independent of its graphenic crystallinity. Expanding the observations described in [10], we show that the presence and number of metallic nanoparticles in the material determine the success of the laser treatment process. We concentrate on the structural changes of the network under laser irradiation and present a comprehensive interpretation of our results regarding the sample's pre-existing anisotropy, the ratio of sample width to laser spot diameter, and the amount of carbonaceous bundle coating in the material.…”

“…Depending on the thickness and density of other samples, the power applied was adjusted to keep the energy delivered per unit weight constant. For further details on the laser processing, please refer to the methods section below and reference [10]. In contrast to [10], where the laser beam was scanned over entire samples, here, in order to isolate effects of a sustained laser heating, we concentrate on single point irradiation experiments where the laser pulses are fixed on one location on the CNT sample.…”

“…Photonic post-processing, as described in [10], was mainly investigated for its ability to selectively sort the CNTs present in a textile sample. Narrow ribbons of CNT textile were suspended between electrodes and briefly illuminated using a laser, causing a rapid temperature rise.…”

Manufacture of Networks from Large Diameter Single-Walled Carbon Nanotubes of Particular Electrical Character

“…BF 3 improves electrical conductivity most probably by introducing an impurity band to the density of states (DOS) similarly to the action of interhalogen compounds [1], which leads to lowering the bandgap of semiconducting CNTs. The reason why semiconducting-rich CNT films did not show an even larger increase in conductivity (as compared with unsorted samples) may be explained by the fact that the electronic transport in these materials is often limited by the contact resistance between individual CNTs, or caused by other extrinsic factors such as CNT misalignment or presence of impurities, as recently reported by Bulmer et al [26].…”