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- ItemIn situ tracking of defect healing and purification of single-wall carbon nanotubes with laser radiation by time-resolved Raman spectroscopy(Cambridge : Royal Society of Chemistry, 2015) Souza, N.; Zeiger, M.; Presser, V.; Mücklich, F.Defects and impurities in carbon nanotubes (CNTs), inherent to all synthesis routes, are generally addressed by thermal and/or chemical post treatments. These require atmosphere control, time-consuming temperature ramping, chemical handling, and often incur further defects. Furthermore, certain applications require nanotube treatments, such as dispersion, that cause further unwanted damage. Laser radiation was found to drastically increase purity, crystallinity and mean inter-defect distance while reducing defects, as indicated by Raman spectroscopy, effectively annealing our single-wall CNTs. Laser power density and radiation times, in other words, fluence, were optimised. When applied to CNTs with mechanically induced defects, these were almost fully eliminated. In addition to the tuned annealing of CNTs, unintentional sample modification can occur during Raman measurements if the influence of the power density and the exposure time are underestimated or disregarded. Fast laser radiation times and simple manipulation outdo common purification treatments. Additionally, selective shape and sitespecific parameters come into play such as interference patterns. Such arrangements of alternating tube quality, that is, in a CNT mat, could be interesting for preferred electronic conduction paths and find applications in, for example, interdigitated electrodes or sensors.
- ItemDispersion analysis of carbon nanotubes, carbon onions, and nanodiamonds for their application as reinforcement phase in nickel metal matrix composites(Cambridge : Royal Society of Chemistry, 2015) Reinert, L.; Zeiger, M.; Suárez, S.; Presser, V.; Mücklich, F.Dispersions of multi-wall carbon nanotubes, onion-like carbon, and nanodiamonds in ethylene glycol are produced using a homogenizer and an ultrasonic bath, altering the treatment time. The dispersed particles are then used as reinforcement phase for nickel matrix composites. These nanoparticles are chosen to represent different carbon hybridization states (sp2 vs. sp3) or a different particle geometry (0D vs. 1D). This allows for a systematic investigation of the effect of named differences on the dispersibility in the solvent and in the composite, as well as the mechanical reinforcement effect. A comprehensive suite of complementary analytical methods are employed, including transmission electron microscopy, Raman spectroscopy, dynamic light scattering, sedimentation analysis, zeta-potential measurements, scanning electron microscopy, electron back scatter diffraction, and Vickers microhardness measurements. It can be concluded that the maximum achievable dispersion grade in the solvent is similar, not altering the structural integrity of the particles. However, nanodiamonds show the best dispersion stability, followed by onion-like carbon, and finally multi-walled carbon nanotubes. The distribution and agglomerate sizes of the particles within the composites are in good agreement with the dispersion analysis, which is finally correlated with a maximum grain refinement by a factor of 3 and a maximum mechanical reinforcement effect for nanodiamonds.