Impedance spectroscopy of short multiwalled carbon nanotube networks deposited on a paper substrate: tracking the evolut
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Impedance spectroscopy of short multiwalled carbon nanotube networks deposited on a paper substrate: tracking the evolution of in-plane and thru-plane electronic properties Rachel L. Muhlbauer1 and Rosario A. Gerhardt1,* 1
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245, USA
Received: 28 July 2020
ABSTRACT
Accepted: 22 October 2020
Multiwalled carbon nanotubes (MWNT) were deposited via dropcasting and dried using vacuum filtration. Because of the slightly larger pore size (5–10 lm) of the paper substrate used as compared to the length of the nanotubes (0.5–2 lm), a variety of MWNT networks were formed both on the surface and through the thickness of the paper. Using a combination of impedance spectroscopy, equivalent circuit modeling, and microscopy techniques, it was possible to describe in detail how the electrical properties change as a function of how the MWNTs are distributed on the porous substrate by varying the number of deposited layers (1–20) as well as the dispersion concentration (0.1–5 mg/ mL). In the in-plane, four different electrical responses were observed and modeled: (1) a substrate dominated spectrum representing unconnected MWNTs, (2) one that included bundle and junction responses as well as some inductances representing sparsely distributed MWNT networks, (3) followed by a parallel RL circuit for partially connected MWNT networks, and (4) finally a series RL circuit for fully connected MWNT networks. In the thru-plane, only two different electrical responses were observed and modeled. The results for the in-plane and thru-plane properties were used to generate percolation curves that show that electrical conductivity can change as much as 10 orders of magnitude for the same exact MWNTs. These results indicate that not only do the characteristics of the nanotubes themselves play a role but also the structure of the underlying substrate and the details of how the films are deposited.
Published online: 2 November 2020
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Springer Science+Business
Media, LLC, part of Springer Nature 2020
Handling Editor: David Cann.
Address correspondence to E-mail: [email protected]
https://doi.org/10.1007/s10853-020-05498-2
3257
J Mater Sci (2021) 56:3256–3267
GRAPHICAL ABSTRACT
Introduction Impedance spectroscopy (IS) is a powerful tool for characterizing the behavior of materials systems. Unlike their DC-based counterparts, AC electrical techniques, including IS, are more sensitive to individual electrical processes present due to the dependence of frequency on the measurement [1]. Because impedance can be measured over a wide range of frequencies (10–3–107 Hz), it is possible to detect different electronic processes active in the material as well as separate the contribution of each process from the overall electronic behavior of the material or film through careful equivalent circuit fitting [2, 3]. It has been previously [4, 5] shown that it is possible to use IS to detect the different electrical processes occurring in carbon
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