High Conductivity Copper–Carbon Nanotube Hybrids via Site-Specific Chemical Vapor Deposition

Site-selective copper nanometal seeding through chemical vapor deposition (CVD) is demonstrated as a viable method in concert with solution electrodeposition of bulk Cu to enhance the electrical conductivity of a porous, low-density (0.12 g/cm3, ～9 mg/m) CNT roving. An electrical bias applied directly to the CNT roving promotes Joule heating, which provides the thermal energy necessary for the decomposition of a bis(tert-butylacetoacetato)copper (Cu(tBAOAC)2) precursor. Localized changes in the resistance within the bulk CNT conductor were used to selectively deposit the precursor at thermally active sites, which were evaluated through thermal imaging. The deposition varies from localized Cu deposits at currents producing average temperatures of ～225 °C to a consistent deposition of 10–40 nm Cu particles at applied currents producing average temperatures >300 °C, far above the threshold for the decomposition of the Cu(tBAOAC)2 precursor. Scanning electron microscopy of a cross section of the roving reveals Cu depositions on the interior of the roving, demonstrating the penetration of the vapor into the CNT network and subsequent decomposition within the roving. A commercial acid-based Cu electroplating solution was used to deposit bulk Cu onto as-prepared and CVD seeded CNT wires, followed by planar densification and H2/Ar annealing. The finished conductors with Cu loadings from ～30 to 95% w/w which combine CVD Cu seeding and electrodeposition result in specific conductivity values 3–5 times higher than Cu-CNT conductors produced by electrodeposition alone. Ultimately, a CNT hybrid conductor with 94.2% w/w Cu achieved a specific conductivity of 5632 S m2/kg and electrical conductivity of 28.1 MS/m—approaching values previously only seen in metallic conductors. Overall, the present results demonstrate the potential of site-specific CVD toward both seeding metal prior to electroplating and as a possible method toward the enhanced nanometal interconnection of carbon conductors (NICCs)