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.
Highlights
We introduce a photonic post-process, tailored to floating catalyst derived carbon nanotube (CNT) textiles, that substantially improves purity, internal alignment and graphitic crystallinity
We found that applying acid with the laser treated FWCNT film still stretched and suspended by its ends by a scaffolding condenses the transparent film into an opaque, uniform fiber and assists in maintaining the high degree of microstructure alignment
The most successful CNT laser treatments involved illuminating unaligned SWCNTs in air supported by a substrate, where often the treating laser was used to probe for Raman spectroscopy[9,11,12,13,37,38,39]
Summary
We introduce a photonic post-process, tailored to floating catalyst derived CNT textiles, that substantially improves purity, internal alignment and graphitic crystallinity. The process may be summed up as natural selection; what survives is a transparent FWCNT film with substantially greater internal microstructure alignment, specific conductivity, and a crystallinity maxed to the resolution limits of the Raman spectrometer. With the unique requirement that the CNT material is elevated off the surface, our laser intensity is several orders of magnitude lower (0.05 kW cm−2 versus 1–100 kWcm−2) with far shorter duration (~ms versus seconds to hours) than the other reports. While considerable crystallinity enhancement is a striking effect shared between this study and possibly the others, the photonic process discussed here uniquely aligns the microstructure, preserves the FWCNT distribution, and substantially improves the conductivity. An oven does not replicate the effect because we show the application of heat must be brief and localized to prevent burning away all the material
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