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Title: Thermal characterization of carbon nanotube fiber by time-domain differential Raman

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Journal Article: Publisher's Accepted Manuscript
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Journal Volume: 103; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-10-04 15:41:32; Journal ID: ISSN 0008-6223
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United Kingdom

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Li, Changzheng, Xu, Shen, Yue, Yanan, Yang, Bing, and Wang, Xinwei. Thermal characterization of carbon nanotube fiber by time-domain differential Raman. United Kingdom: N. p., 2016. Web. doi:10.1016/j.carbon.2016.03.003.
Li, Changzheng, Xu, Shen, Yue, Yanan, Yang, Bing, & Wang, Xinwei. Thermal characterization of carbon nanotube fiber by time-domain differential Raman. United Kingdom. doi:10.1016/j.carbon.2016.03.003.
Li, Changzheng, Xu, Shen, Yue, Yanan, Yang, Bing, and Wang, Xinwei. 2016. "Thermal characterization of carbon nanotube fiber by time-domain differential Raman". United Kingdom. doi:10.1016/j.carbon.2016.03.003.
title = {Thermal characterization of carbon nanotube fiber by time-domain differential Raman},
author = {Li, Changzheng and Xu, Shen and Yue, Yanan and Yang, Bing and Wang, Xinwei},
abstractNote = {},
doi = {10.1016/j.carbon.2016.03.003},
journal = {Carbon},
number = C,
volume = 103,
place = {United Kingdom},
year = 2016,
month = 7

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Publisher's Version of Record at 10.1016/j.carbon.2016.03.003

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  • A novel transient thermal characterization technology is developed based on the principles of transient optical heating and Raman probing: time-domain differential Raman. It employs a square-wave modulated laser of varying duty cycle to realize controlled heating and transient thermal probing. Very well defined extension of the heating time in each measurement changes the temperature evolution profile and the probed temperature field at μs resolution. Using this new technique, the transient thermal response of a tipless Si cantilever is investigated along the length direction. A physical model is developed to reconstruct the Raman spectrum considering the temperature evolution, while taking intomore » account the temperature dependence of the Raman emission. By fitting the variation of the normalized Raman peak intensity, wavenumber, and peak area against the heating time, the thermal diffusivity is determined as 9.17 × 10⁻⁵, 8.14 × 10⁻⁵, and 9.51 × 10⁻⁵ m²/s. These results agree well with the reference value of 8.66 × 10⁻⁵ m²/s considering the 10% fitting uncertainty. The time-domain differential Raman provides a novel way to introduce transient thermal excitation of materials, probe the thermal response, and measure the thermal diffusivity, all with high accuracy.« less
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  • Here, the properties of carbon nanotube (CNT) networks and analogous materials comprising filamentary nanostructures are governed by the intrinsic filament properties and their hierarchical organization and interconnection. As a result, direct knowledge of the collective dynamics of CNT synthesis and self-organization is essential to engineering improved CNT materials for applications such as membranes and thermal interfaces. Here, we use real-time environmental transmission electron microscopy (E-TEM) to observe nucleation and self-organization of CNTs into vertically aligned forests. Upon introduction of the carbon source, we observe a large scatter in the onset of nucleation of individual CNTs and the ensuing growth rates.more » Experiments performed at different temperatures and catalyst particle densities show the critical role of CNT density on the dynamics of self-organization; low-density CNT nucleation results in the CNTs becoming pinned to the substrate and forming random networks, whereas higher density CNT nucleation results in self-organization of the CNTs into bundles that are oriented perpendicular to the substrate. We also find that mechanical coupling between growing CNTs alters their growth trajectory and shape, causing significant deformations, buckling, and defects in the CNT walls. Therefore, it appears that CNT–CNT coupling not only is critical for self-organization but also directly influences CNT quality and likely the resulting properties of the forest. As a result, our findings show that control of the time-distributed kinetics of CNT nucleation and bundle formation are critical to manufacturing well-organized CNT assemblies and that E-TEM can be a powerful tool to investigate the mesoscale dynamics of CNT networks.« less
  • Ion irradiation effects on thermal property changes are compared between aligned carbon nanotube (A-CNT) films and randomly entangled carbon nanotube (R-CNT) films. After H, C, and Fe ion irradiation, a focusing ion beam with sub-mm diameter is used as a heating source, and an infrared signal is recorded to extract thermal conductivity. Ion irradiation decreases thermal conductivity of A-CNT films, but increases that of R-CNT films. We explain the opposite trends by the fact that neighboring CNT bundles are loosely bonded in A-CNT films, which makes it difficult to create inter-tube linkage/bonding upon ion irradiation. In a comparison, in R-CNTmore » films, which have dense tube networking, carbon displacements are easily trapped between touching tubes and act as inter-tube linkage to promote off-axial phonon transport. The enhancement overcomes the phonon transport loss due to phonon-defect scattering along the axial direction. A model is established to explain the dependence of thermal conductivity changes on ion irradiation parameters including ion species, energies, and current.« less