The importance of carbon nanotube wire density, structural uniformity, and purity for fabricating homogeneous carbon nanotube–copper wire composites by copper electrodeposition

We present the influence of density, structural regularity, and purity of carbon nanotube wires (CNTWs) used as Cu electrodeposition templates on fabricating homogeneous high-electrical performance CNT–Cu wires lighter than Cu. We show that low-density CNTWs (<0.6 g/cm3 for multiwall nanotube wires) with regular macro- and microstructures and high CNT content (>90 wt %) are essential for making homogeneous CNT–Cu wires. These homogeneous CNT–Cu wires show a continuous Cu matrix with evenly mixed nanotubes of high volume fractions (∼45 vol %) throughout the wire-length. Consequently, the composite wires show densities ∼5.1 g/cm3 (33% lower than Cu) and electrical conductivities ∼6.1 × 104 S/cm (>100 × CNTW conductivity). However, composite wires from templates with higher densities or structural inconsistencies are non-uniform with discontinuous Cu matrices and poor CNT/Cu mixing. These non-uniform CNT–Cu wires show conductivities 2–6 times lower than the homogeneous composite wires.