Microwave Conductivity of Sorted CNT Assemblies

Abstract

Recent progress with tailored growth and post-process sorting enables carbon nanotube (CNT) assemblies with predominantly metallic or semi-conducting concentrations. Cryogenic and microwave measurements performed here show transport dimensionality and overall order increasing with increasing metallic concentration, even in atmospheric doping conditions. By 120 GHz, the conductivity of predominantly semi-conducting assemblies grew to 400% its DC value at an increasing growth rate, while other concentrations a growth rate that tapered off. A generalized Drude model fits to the different frequency dependent behaviors and yields useful quality control parameters such as plasma frequency, mean free path, and degree of localization. As one of the first demonstrations of waveguides fabricated from this material, sorted CNTs from both as-made and post-process sources were inserted into sections of practical micro-strip. With both sources, sorted CNT micro-strip increasingly outperformed the unsorted with increasing frequency-- illustrating that sorted CNT assemblies will be important for high frequency applications.

Investigating the Broadband Microwave Absorption of Nanodiamond Impurities

“…Since bulk carbon is a very good conductor it seems sensible that there may be conduction loss mechanisms. However, at high frequencies the charge transport can be heavily dependent upon the disordered surfaces as opposed to the free or static conductivity measured at low frequencies [22]. Determination of whether free electron conduction or losses from the disorder plays a role in the microwave absorption can be identified using the model relating relative complex permittivity to conductivity, derived from Maxwell's equations (2) where is the effective free electron conductivity, is the effective dielectric constant and is the additional loss contribution related to the disordered surfaces.…”

“…, where in this study the onset frequency and the fitting parameters ( and ) are simply lumped into [22]. Therefore, free electron conductivity shows a characteristic dependence.…”

Electrical sensing of DNA-hybridization using two-port network based on suspended carbon nanotube membrane

“…Only pure semiconducting SWCNT transistors worked well on this mechanism with an acceptable sensitivity because the metallic or mixed CNTs are too conductive to reflect the tiny charge variations brought by DNA hybridization. However, the implementation of pure semiconducting SWCNT was not very feasible due to the limitations of current CNT sorting technology (Bulmer et al 2014;Hui et al 2015).…”

Microwave conductance of aligned multiwall carbon nanotube textile sheets

“…A Drude-like mechanism is also consistent with AC results reported for SWNT "mats." 18 However, AC results on several other SWNT formats [13][14][15][16][17] report an AC conductance having a sub-linear frequency dependence Y(f) / f s for 0 < s < 1 from 1 to 50 GHz. This behavior is interpreted as "universal disorder" AC dynamics 19 27 SWNTs, 28 and SWNT/MWNT mixtures at high densities and low frequencies.…”

“…Microwave conductance has been measured on many types of single wall nanotube (SWNT) materials in the form of self-assembled arrays, 13,14 thin-film networks, 15,16 and semiconducting and metallic SWNT "paper" 17 and "mats." 18 Interestingly, the microwave conductance of SWNTs in the tens of GHz range in most, [13][14][15][16][17] but not all 18 these formats, has been described by a "universal disorder" or glass-like electrodynamic response. 19 Whether a similar AC conduction mechanism holds for MWNT textiles has not been known until now.…”