Millimeter-Tall Carpets of Vertically Aligned Crystalline Carbon Nanotubes

We synthesized millimeter-tall, dense carpets of crystalline CNTs on nonpolished copper substrates with a thin Al2O3 (below 10 nm) underlayer and Fe (1.2 nm) layer as a catalyst using chemical vapor deposition (CVD). Preheating of the hydrocarbon precursor gases and in-situ formation of controlled amounts of water vapor were critical process parameters. High-resolution microscopy showed that the CNTs were crystalline with lengths up to a millimeter. Electrical conduction between the CNTs and the copper substrate was demonstrated using multiple methods (probe station, electrodeposition, and hydrolysis of water). Through TEM characterizations of cross sections, we demonstrated that copper diffusion into the alumina layer during the thermal process was the key to explain the observed electrical conductivity. Additionally, the high electrical conductivity of a thermally processed sample compared to the insulating behavior of a pristine sample confirmed the mechanistic hypothesis. Adsorption isotherm measurements showed the mesoporous structure of the vertically aligned carbon nanotubes (VACNTs) with a surface area of 342 m2/g. Electrical conduction and high surface area of this nanostructure make it a promising platform to be functionalized for future battery electrodes.