Microstructure and electromagnetic characteristics of Ni nanoparticle film coated carbon microcoils

Abstract Carbon microcoils (CMCs) have been coated with a Ni nanoparticle film using an electroless plating process. The morphology, the elemental composition and the phases in the coating layer, complex permittivity and permeability of the CMCs and Ni-coated CMCs were, respectively, investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and microwave vector network analysis at room temperature. A homogeneous dispersion of Ni nanoparticles on the outer surface of the CMCs was obtained, with a mean particle size of ∼34.4 nm and the phosphorus content of about 8.5 wt%. When comparing the coated and uncoated CMC samples, the real ( ɛ ′) and imaginary ( ɛ ″) part of the complex permittivity as well as dielectric dissipation factor ( tgδ ɛ  =  ɛ ″/ ɛ ′) of the Ni-coated CMCs were much smaller, while the real ( μ ′) and imaginary ( μ ″) part of the complex permeability and the magnetic dissipation factor ( t g σ μ = μ ″ / μ ′ ) were larger. The enhanced microwave absorption of Ni-coated CMCs resulted from stronger dielectric and magnetic losses. In contrast, the microwave absorption of uncoated CMCs was mainly attributed to the dielectric rather than magnetic losses.