Extreme Magneto-transport of Bulk Carbon Nanotubes in Sorted Electronic Concentrations and Aligned High Performance Fiber

John S Bulmer,Agnieszka Lekawa-Raus,Krzysztof K Koziol,Fedor F Balakirev,Dwight G Rickel

doi:10.1038/s41598-017-12546-6

Abstract

We explored high-field (60 T) magneto-resistance (MR) with two carbon nanotube (CNT) material classes: (1) unaligned single-wall CNTs (SWCNT) films with controlled metallic SWCNT concentrations and doping degree and (2) CNT fiber with aligned, long-length microstructure. All unaligned SWCNT films showed localized hopping transport where high-field MR saturation definitively supports spin polarization instead of a more prevalent wave function shrinking mechanism. Nitric acid exposure induced an insulator to metal transition and reduced the positive MR component. Aligned CNT fiber, already on the metal side of the insulator to metal transition, had positive MR without saturation and was assigned to classical MR involving electronic mobility. Subtracting high-field fits from the aligned fiber’s MR yielded an unconfounded negative MR, which was assigned to weak localization. It is concluded that fluctuation induced tunnelling, an extrinsic transport model accounting for most of the aligned fiber’s room temperature resistance, appears to lack MR field dependence.

Highlights

Compounds, in some cases surpassing the conductivity of copper at room temperature, had a host graphitic structure with a graphitic crystallinity beyond the resolution capability of X-ray diffraction and Raman spectroscopy
In14 we proposed that single-wall CNTs (SWCNT) based textiles may approach this degree of graphitic crystallinity, where Raman spectroscopy looses resolution and other techniques, such as high magnetic field characterization, may become necessary for quality control
This study primarily focused on unaligned films with a metallic SWCNT concentration of 95% and the typical unsorted metallic concentration of 33%, limited transport measurements were accomplished with a 98% semi-conducting SWCNT film

Summary

Introduction

Compounds, in some cases surpassing the conductivity of copper at room temperature, had a host graphitic structure with a graphitic crystallinity beyond the resolution capability of X-ray diffraction and Raman spectroscopy. Note that the drastic difference between films in the zero-field resistance versus temperature plots (to be shown later) qualitatively confirm the sorting process between unsorted, predominantly semi-conducting SWCNTs, and predominantly metallic SWCNTs. As-is samples, taken after initial transport measurements, were chemically treated with 70% nitric acid, a well-established CNT dopant[15,23,24].

Results

Conclusion