(259f) Electrochemical Synthesis of Bulk Copper-Carbon Nanotube Composites

As electronics are driven towards progressively smaller scales and higher speeds, bulk metals such as copper are reaching their material performance limits. The use of metal composites with ultraconductive nanomaterials, particularly carbon nanotubes (CNTs), is becoming increasingly appealing to make fast, efficient devices with high electrical and thermal performance. However, fully aligned, densely-packed CNT assemblies within metal networks are required to generate optimal wiring and electronic structures. Even small microstructural defects can cause large losses in mechanical strength and electrical/thermal transport, which constrains the range of processing strategies that can be employed. To address this challenge, we are studying the homogeneous nucleation of Cu within preformed CNT mats by electrodeposition.

In this work, we introduce a new method to create a uniform Cu-CNT composite from an isotropic CNT mat in single step electrodeposition using an electrolyte solution modified to have a marginally wetting contact angle. We first describe the requirements to transition from nonwetting to wetting systems using chemical additives to our electrolyte solution, and how these additives influence the Faradaic efficiency of electrodeposition, appearance of copper nucleation, percolation, and final composite conductivity. We describe the limits of Cu penetration into dense initial CNT networks using electron dispersion spectrographs of cross-sections of experimental specimens.

We conclude by introducing a processing diagram mapping of the copper deposition mass and composite conductivity as a function of the input current density and time of application of current. We achieve control of the final conductivity over several orders of magnitude up to 2 MS/m for a lightweight composite with density up to 0.8 g/cm3. We finally discuss the limits to homogeneous Cu concentration and process speed, and reflect on requirements to turn this into a scalable process, e.g., for scalable Cu-CNT wire manufacturing.