High-Aspect-Ratio Metal Microfabrication by Nickel Electroplating of Patterned Carbon Nanotube Forests

High-aspect-ratio metallic microstructures have a variety of potential applications in sensing and actuation. However, fabrication remains a challenge. We have fabricated nickel microstructures with over 20:1 aspect ratios by electroplating patterned carbon-coated carbon-nanotube forests using a nickel chloride bath. Pulse plating allows nickel ions to diffuse into the interior of the forest during off portions of the cycle. Done properly, this solves the problem of the formation of an external crust, which otherwise blocks nickel deposition in the interior of the structures. Thus, densities of 86 ± 3% of bulk Ni for the composite structures are achieved. Cantilever structures do not yield under load, but break. Measurements of the material properties of this composite material indicate an elastic modulus of ∼42 GPa and a strength of 400 MPa. We demonstrate the utility of this method with an external field magnetic actuator consisting of a proof mass and two flexures. We achieved 1-mN actuation forces.