Resonant and Broadband Microwave Permittivity Measurements of Single-walled Carbon Nanotubes
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Resonant and Broadband Microwave Permittivity Measurements of Single-walled Carbon Nanotubes Chinmay D. Darne1,2, Lei-Ming Xie2, Divya Padmaraj1,2, Paul Cherukuri3, Wanda ZagozdzonWosik1,2, and Jarek Wosik1,2 1 Department of Electrical and Computer Engineering, University of Houston, Houston, TX, 77204 2 Texas Center for Superconductivity, University of Houston, Houston, TX, 77204 3 Department of Chemistry, Rice University, Houston, TX, 77005 ABSTRACT We report on complex permittivity measurements of single-walled carbon nanotubes (SWNTs) over the microwave frequency range. The SWNT samples contained a mixture of semiconducting and metallic nanotubes and were homogeneously suspended using surfactant (Pluronic, F108). Other samples that were characterized included a Pluronic powder and a carpet of oriented multi-walled nanotubes (MWNT). Shielded open-circuited transmission line technique was used for broadband frequency measurements. Single frequency (resonant) measurements for SWNT samples were carried out by using two specially designed microwave dielectric resonators (DR). The first DR, with an axial cylindrical hole in the dielectric disk, could excite either TE011 or TM011 mode (3.4 GHz and 6 GHz) and was designed for liquid/powder sample characterization. The second DR used was split-post dielectric resonator (12 GHz). At 3.4 GHz, the real and imaginary parts of permittivity for Pluronic only suspended SWNTs were experimentally found to be 3.5 and 0.72, respectively. From our calculations conductivity of SWNT mixture was 1.16x105 (S/m) and for Pluronic it was 1.6587x10-2 (S/m). INTRODUCTION In the last few years carbon nanotubes emerged as one of the highly investigated materials, primarily due to their quasi-one dimensional structure, superior mechanical and chemical properties and most importantly their tunable electronic nature (by altering their chirality and diameter). Properties of single-walled carbon nanotubes (SWNTs) are of special interest and great consequence because of their potential applications in various microwave frequency ranges as microwave lenses, high-speed nanoelectronic devices, antennas, waveguides, nano-electromechanical systems (NEMS), etc. [1]. Recent studies have shown that high current density combined with flat conductivity response (from dc to 10 GHz) for SWNTs make them an ideal candidate for high-speed transistor applications [2]. Due to their superior conductivity, efforts are being made to incorporate nanotubes as interconnects in future microelectronic devices. SWNTs can also be used as electromagnetic interference (EMI) shields in high-frequency circuits and as low-reflectivity materials for military applications. The excellent conductivity of the nanotubes coupled with their high aspect ratio helps to drastically reduce their loading density in composites and thus make them a very good alternative to the currently employed carbon black [1,3,4]. Theoretical calculations performed for static polarizabilities of metallic SWNTs have shown that the polarizability
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