Electrical Transport Behaviors of Ni Layer on Carbon Fiber

Recently, carbon materials have been employed for the core of metal wires, contributing to their weight reduction. Low weight is a required characteristic for cables used in air, water, and ground transportations, in order to maximize fuel efficiency. Nowadays, the hybridization of C with metal for the creation of C-based metal wires is achieved through different approaches. A thin metal layer of Ni is usually applied through electroless plating on the surface of C fibers (CFs; diameter = 7 μm). Transport studies conducted on a single strand of Ni-coated CFs (Ni-CF) have indicated that, depending on the grain size, phonon-supported hopping or phonon-driven electron scattering transport can dominate. At a given P concentration (∼11 at.wt.%) and when the average grain size is < 100 nm, phonon-driven electron scattering transport dominates: as the temperature increases, the resistance increases as well, resulting in a positive temperature coefficient of resistance (TCR) (∼1.5 × 10−3/K at 300 K). This is a conduction behavior typically observed in metals. However, when the average grain size is > 100 nm, impurity-related variable range hopping (VRH) transport dominated, leading to a negative TCR (∼1.0 × 10−4/K at 300 K); in this case, the resistance decreases with increasing temperature, as in a semiconductor. Our results imply that, by controlling the plating condition and surface morphology of CF, it is possible to modulate metal properties (i.e., the metal-insulator transition (MIT)).