Impact of dynamic density decay of growing carbon nanotube forests on electrical resistivity

Abstract

Vertically aligned carbon nanotube (CNT) forests densely formed on diverse metallic substrates are desirable as large-area electrodes and thermal interface materials. In this study, we achieved high-density CNT forests on stainless steel and Cu substrates by preventing the interaction between the metallic elements and Fe catalysts at high temperatures. We found that coating the substrate surface with a combination of Ta and SiO2 effectively suppressed the diffusion of metallic elements of the substrate to the catalytic layer. The macroscopic electrical resistivity of longer forests was found to increase as the number density of CNTs decreased during the growth process. This increase in resistivity was reproduced by the dynamic density decay model in which CNT density decreases with forest growth. We point out the importance of the relationship between the length and density of CNT forests for applications.