Joining Of Carbon Nanotube Fibers Via Meniscus Confined Electrochemical Deposition

Advances in production techniques of continuous fibers made purely of carbon nanotubes(CNTs),have paved the way for new macroscale applications which utilize the superior performances of individual CNTs.Theses wire-like macroscopic assemblies of axially aligned CNTs have showed significant potential to be used in electrical wires and cables,flexible high-performance supercapacitors and solar cells,and specialty composites.A necessary step for the varieties of electrical and electronic applications of CNT fibers is to join them with other live parts of the circuits electrically and mechanically.However,there have not been any precise and reliable joining methods developed for CNT fibers.Aiming at this key issue,this work developed a novel method that utilizes the meniscus confined electrochemical deposition(MC-ECD)to successfully fabricate low-resistance and mechanically strong connections of CNT fibers to metal substrates or to other CNT fibers in an ambient air environment.The morphologies,microstructures and properties of the joints fabricated were investigated systematically.The key process parameters were settled and the related mechanisms were analysed.The meniscus remained stable during MC-ECD process.The deposited joints have regular shapes with sizes close to the dispensing nozzle sizes of the capillary tube anodes.The copper deposit with a uniform and compact microstructure clings tightly to the fiber surface with a distinct interface forming between the copper deposit and the fiber.The original CNT networks of the fibers can remain largely unchanged after the joining process.The joint between a CNT fiber and a metal substrate consists of four parts: the substrate,the deposition layer,the cladding layer and the CNT fiber.The copper deposit shows columnar growth.The copper grains of the deposition layer grew vertically from the substrate surface,meanwhile the grains of the cladding layer grew along the radial direction of the CNT fiber.The surface roughness value of the joint can be as low as 79.67 nm.The electrical resistance of an individual joint with an average diameter of 725 μm was evaluated to be about 1.35 Ω via a modified transmission line method.Three failure modes were observed from the tensile tests of several joints fabricated under different conditions.If the copper deposit is thick enough,the peak load of the joint approaches that of the fiber.During MC-ECD process,the copper atoms nucleated mainly along the edges of crystal planes and also on the flat crystal planes.The growth and extension of the crystal nuclei at the edges of crystal planes combined with the growth of the two-dimensional crystal nuclei on the crystal planes make the copper grains grow vertically.Meanwhile,the horizontal growth of grains depends on the nucleation and growth at the edges of crystal planes.Two copper deposit cladding layers grew together with a bonding surface to finally form a joint between two CNT fibers.The grains of each deposit cladding layer showed columnar growth along the radial direction of the fiber.There are generally four kinds of joints.Good surface quality can be obtained with a surface roughness value as low as 0.183 μm.The electrical resistance of an individual joint with a length of 365 μm was evaluated to be about 6.5 Ω,which is much lower than that of the fiber with the same length.For the joints fabricated with separation distances and bottom clearances,the fibers fractured at locations away from the joints during tensile tests,and the joints showed peak loads close to those of the fibers.Moreover,in addition to the joints between single CNT fibers with various diameters and metal substrates,the MC-ECD method developed in this study can fabricate the reliable joints between two CNT fibers and metal substrates in different ways and between two CNT fibers with different diameters,which shows a good versatility.