Microwave absorption properties of carbon fibers with carbon coils of different morphologies (double microcoils and single nanocoils) grown on them

Double-carbon microcoils and single-carbon nanocoils were selectively grown on the surface of carbon fibers (CFs) via decomposition of acetylene at the temperature of 680 °C using Ni and Ni/Al2O3 catalysts, respectively. The morphology and microstructure of the as-prepared carbon coils–CFs were studied by SEM and Raman spectra, and the microwave absorption properties were also examined. Different from the double-carbon microcoils, no catalyst is observed at the growth tip of single-carbon nanocoils. It is considered that the Ni/Al2O3 binary catalysts would induce base growth model where only one remaining side of the catalyst particle contributes to nanofiber’s growth, resulting in the formation of single-carbon nanocoil. The single-carbon nanocoils–CFs composite shows lower complex permittivity, larger chirality admittance, as well as better microwave absorption properties than those of double-carbon microcoils–CFs. The maximum RL of the single-carbon nanocoils–CFs composite is −41.2 dB, and the bandwidth of RL less than −10 dB is up to 9.6 GHz, which are also better than those of other carbon nanomaterials in the literature.