Ab Initio Study of Iodine-Doped Carbon Nanotube Conductors

Abstract

The widespread use of copper in power and data cabling for aircraft, ships, and ground vehicles imposes significant mass penalties and limits cable ampacity. Experimental research has suggested that iodine-doped carbon nanotubes (CNTs) can serve as energy efficient replacements for copper in mass sensitive cabling applications. The high computational costs of ab initio modeling have limited complimentary modeling research on the development of high specific conductance materials. In recent research, the authors have applied two modeling assumptions, single zeta basis sets and approximate geometric models of the CNT junction structures, to allow an order of magnitude increase in the atom count used to model iodine-doped CNT conductors. This permits the ab initio study of dopant concentration and dopant distribution effects, and the development of a fully quantum based nanowire model which may be compared directly with the results of macroscale experiments. The accuracy of the modeling assumptions is supported by comparisons of ballistic conductance calculations with known quantum solutions and by comparison of the nanowire performance predictions with published experimental data. The validated formulation offers important insights on dopant distribution effects and conduction mechanisms not amenable to direct experimental measurement.

Carbon Nanotube Coated Conductors

“…Included within these processes is the need to functionalize the CNTs to both increase their conductivities and minimize the interfacial resistance between them. 6,7 The process-dependent variability in both of these areas, further coupled with the different types of CNTs that can be employed for conductor fabrication, is responsible for the wide range of resistivity values reported in the literature for various conductor approaches. 5,8−14 Many approaches for full or partial replacement of traditional engineering materials have been demonstrated with CNTs.…”

“…Technologically useful conductors will require material forms where the CNTs are highly aligned and tightly packed together to maximize the amount of active or connected interfacial area within a conductive assembly. Included within these processes is the need to functionalize the CNTs to both increase their conductivities and minimize the interfacial resistance between them. , The process-dependent variability in both of these areas, further coupled with the different types of CNTs that can be employed for conductor fabrication, is responsible for the wide range of resistivity values reported in the literature for various conductor approaches. ,− …”

Potassium-Doped Graphene Nanoribbons for High-Specific Conductivity Wiring

“…The other essential modeling inputs are a geometry model for the "nanowire" and scaling information, since the quantum calculations are made at the nanoscale. This subsection extends previous work 13 (focused on CNT-based nanowires) to the GNR-based nanowire case, adopting the simplest possible set of geometric and scaling assumptions needed to estimate the macroscale (experimentally measured) performance of doped graphene-based conductors. The nanowire modeling results are presented in the form of an expected macroscale performance range, recognizing that macroscale carbon conductors consist of bundles or assemblies of nanowires, as opposed to a uniform crystal.…”

“…Only 6-zGNR junctions were modeled at the higher of the two doping densities discussed in the preceding section. Previous modeling work on both nanotube , and GNR junctions , has suggested that junction conductance can be a sensitive function of nanoconductor overlap and that low junction conductance can severely limit carbon nanowire performance. Hence the effects of potassium doping on the GNR junction conductance, as a function of GNR overlap, are of central interest.…”

“…Despite considerable success in improving the conductivity of CNT-based wiring, the development of high-specific conductivity CNT-based wiring has proven to be very difficult. Recent computational work on CNT-based wiring , indicates that dopant distribution effects, variations in electrical properties with CNT diameter, parasitic mass effects for multiwall tubes, and the conductivity properties of doped CNT interfaces (junctions) are the most important factors limiting the mass specific performance of CNT-based wiring. Note that for the CNT bundles which typically make up the tested cables, direct measurement of the effects of these variables on mass specific conductivity is not possible.…”