Electrical transport measurements of highly conductive nitrogen-doped multiwalled carbon nanotubes/poly(bisphenol A carb
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Donghui Zhang Department of Chemistry, Louisiana State University, New Orleans, Louisiana 70803
Seamus A. Curran Department of Physics, University of Houston, Houston, Texas 77004 (Received 2 August 2011; accepted 26 September 2011)
Nitrogen-doped multiwalled carbon nanotubes with poly(bisphenol A carbonate) composites were prepared through simple solution blending. The scaling law, which is based on the percolation theory, is used to describe the electrical conductivities of the composites. Both direct current and alternating current conductivities are in good agreement with the unprecedented high saturated conductivities of the pristine samples (rsat 5 ;734 scm1, pc 5 0.19 wt%). We attributed the high conductivities to the binding of nanotubes into large but tight bundles, which enable the composites to carry more charges. This is notably different from the conventional method, which focuses on forming a well-dispersed three-dimensional network resulting in the conductivities having a lower order of magnitude.
I. INTRODUCTION 1,2
Since the discovery of carbon nanotubes (CNTs), considerable progress has been made toward understanding their unique physical, electrical, and spectral properties.3,4 Owing to these unique properties, CNTs are considered promising materials for various applications.4 Introducing defects or impurities (dopants) into CNTs may manipulate the electronic properties of the CNTs and make them an ideal material for building electronic devices, such as solar cells and field effect transistors.4 Carbon nitride (CNx) nanotubes have received special attention because they retain their metallic properties regardless of their diameter and chirality, as predicted and observed through scanning tunneling microscopy.5–7 For instance, the current–voltage curve of CNx showed higher conductance than that of multiwalled CNTs (MWCNTs).6,7 In addition, both the morphology and chemical composition of CNx nanotubes strongly depend on the syntheses method.4 Although nanotubes cannot be easily doped with nitrogen, many approaches have been used to introduce nitrogen atoms into CNTs, including pyrolysis of nitrogen-rich organic chemicals, magnetron sputtering, and arc discharge in a nitrogen atmosphere.8,9 Different techniques were used to characterize the chemical bonding and electronic structures of CNx nanotubes;
these techniques include atomic force microscopy and Raman spectroscopy.9 In this study, we investigated both direct current (DC) and alternating current (AC) electrical transport properties of nonpurified and chemically purified nitrogendoped MWCNTs (N-MWCNTs) with poly(bisphenol A carbonate) composites at different nanotube weight fractions. II. EXPERIMENTAL
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.355
N-MWCNTs (100 mg) (Wake Forest University, CVD) were refluxed in HNO3/H2O (1:3, v:v, 20 mL) for 8–10 h. The suspension was diluted with deionized (DI) water until its pH 5 5. The filtered N-MWCNTs were then stirred in HCl/H2O (1:3, v:v, 12 mL) for an
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