Improved Characterization of Aqueous Single-Walled Carbon Nanotube Dispersions Using Dynamic Light Scattering and Analytical Centrifuge Methods

Aqueous dispersions of single-walled carbon nanotubes (SWCNTs) with a surfactant were studied by using a combination of differential sedimentation and dynamic light scattering methods. When applied to elongated particles like SWCNTs, the differential sedimentation method makes it possible to measure their diameters in dispersions, while the dynamic light scattering method allows to measure their lengths. Both methods have logarithmic dependence on the ratio between the length and diameter of the particles, and their simultaneous use improves the accuracy of measuring particles’ dimensions. It was shown that sonication of dispersions leads not only to unbundling of agglomerates into individual nanotubes but also to a decrease in their lengths and the appearance of new defects detectable in increasing the D/G ratio in the Raman spectra. Unbundling into individual nanotubes occurs after exposure to 1 kWh/L energy density, and the single nanotube diameter with SDBS is ca. 3.3 nm larger than that of the naked nanotubes. Conductivity of thin SWCNT films made out of individual nanotubes demonstrates a power law dependence with the exponent close to the theoretical one for rigid rods

n‑Type Doping of Triethylenetetramine on Single-Wall Carbon Nanotubes for Transparent Conducting Cathodes

Transparent conductive electrodes (TCEs) are fundamental components for designing flexible electronics and displays. TCEs should exhibit high electrical conductivity, optical transparency, mechanical flexibility, and a suitable work function (WF) for efficient performance. Because of their unique mechanical, electrical, and optical properties, sparse single-wall carbon nanotube (SWCNT) networks are attractive candidates for TCEs. However, to achieve a highly conductive sparse network, a reduction of the junctions’ resistances between the SWCNTs is required. In addition, SWCNTs inherently possess a high WF, which is fundamental for functional anodes but not suitable for cathodes. In this work, n-type doping of SWCNTs via coordinative bonding of triethylenetetramine (TETA) to their surface is introduced to tune both the WF and the junctions’ resistance. A self-developed conductive atomic force microscopy (cAFM) technique is used to investigate the same individual junctions in SWCNT networks before and after exposure to TETA fumes and post heating. The mechanisms by which TETA doping modifies the “global” properties of SWCNT networks are studied by Kelvin probe microscopy, X-ray photoemission spectroscopy (XPS), Raman spectroscopy, and ultraviolet–visible spectroscopy. Following TETA doping, improved conductivity and reduced WF are achieved, implying n-type charge-transfer doping. These results provide a significant step toward the use of SWCNTs as transparent cathodes in organic-based electronic devices