Nanofabrication by electrochemical routes of Ni-coated ordered arrays of carbon nanotubes

Ordered arrays of carbon nanotubes (CNT) have been coated by Ni nanoparticles and Ni thin films by using the chronoamperometry technique for nickel reduction. Two different kinds of nanotube arrays have been used: aligned bundles of CNT grown on Si substrates by chemical vapour deposition (CVD) and networks of CNT bundles positioned via a dielectrophoretic post-synthesis process between the electrodes of a multifinger device. The morphology and structure of the Ni-coated CNT bundles have been characterized by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). By changing the parameters of the electrochemical process, it is possible to modulate the morphological characteristics of the Ni deposits, which can be obtained in form of nanoparticles uniformly distributed along the whole length of the CNT bundles or of Ni thin films. A qualitative study of the nucleation and growth mechanism of Ni onto CNT has been performed using the theoretical model for diffusion-controlled electrocrystallization, and a correlation between growth mechanism and samples morphology is presented and discussed. The possibility to maintain the architecture of the pristine nanotube deposits after the Ni coating process opens new perspectives for integration of CNT/Ni systems in magnetic and spintronics devices.