Mapping carbon nanotube orientation by fast fourier transform of scanning electron micrographs

Abstract

Please cite this article as: E. Brandley, E.S. Greenhalgh, M.S.P. Shaffer, Q. Li, Mapping carbon nanotube orientation by fast fourier transform of scanning electron micrographs, Carbon (2018), doi: 10.1016/j.carbon.2018.04.063. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractA novel method of applying a two-dimensional Fourier transform (2D-FFT) to SEM was developed to map the CNT orientation in pre-formed arrays. Local 2D-FFTs were integrated azimuthally to determine an orientation distribution function and the associated Herman parameter. This approach provides data rapidly and over a wide range of lengthscales.Although likely to be applicable to a wide range of anisotropic nanoscale structures, the method was specifically developed to study CNT veils, a system in which orientation critically controls mechanical properties. Using this system as a model, key parameters for the 2D-FFT analysis were optimised, including magnification and domain size; a model set of CNT veils were pre-strained to 5%, 10% and 15%, to vary the alignment degree. The algorithm confirmed a narrower orientation distribution function and increasing Herman parameter, with increasing pre-strain.To validate the algorithm, the local orientation was compared to that derived from a common polarised Raman spectroscopy. Orientation maps of the Herman parameter, derived by both methods, showed good agreement. Quantitatively, the mean Herman parameter calculated using the polarised Raman spectroscopy was 0.42±0.004 compared to 0.32±0.002 for the 2D-FFT method, with a correlation coefficient of 0.73. Possible reasons for the modest and systematic discrepancy were discussed.

Melt-Spun Nanocomposite Fibers Reinforced with Aligned Tunicate Nanocrystals

“…Raman spectroscopy is known to be a powerful tool for the determination of the orientation of crystalline structures. It has been employed for the evaluation of the alignment of carbon nanotubes [60,61], crystalline polymers [62][63][64], or cellulose nanocrystals [65][66][67][68]. The most intense band in the cellulose spectrum is located at 1095 cm −1 , arising from the vibrations of the C-C and C-O bonds of the polymer backbone [10,33,69].…”

Chemical and topographical patterns combined with solution shear for selective-area deposition of highly-aligned semiconducting carbon nanotubes

“…Alignment of s-CNTs in these arrays was characterized by two-dimensional fast Fourier transform (2D FFT) analysis of SEM images for the deposited s-CNT arrays. In the literature 2D FFT analysis has been used for characterizing alignment of various types of fibrous materials 46,47 including CNT arrays 48 . Details of the 2D FFT methodology are in ESI Fig.…”

Microstructure-properties relations for hierarchically structured CNT fibres

“…In this regard, polarized Raman spectroscopy has been widely used to measure orientation of CNT based materials [78,103,39,11]. For this purpose, a generalized criteria has been classically established.…”

“…This fact leads to a much more less time consuming experiment which, moreover, allow us to obtain information about orientation from each point of the sample. Thus, orientation mapping has been carried out on CNT films using Liu's approach [11]. Accordingly, it seems logic that Liu's approximation would be used instead of the standard method.…”

“…Therefore, until the problem of measuring orientation by Raman is solved, the use of SAXS or WAXS is necessary. There might be an alternative associated to the use of FFT-SEM pictures during in-situ SEM mechanical tests [11]. However, this technique is in a very preliminary step and it needs to be further studied.…”