Ni nanospheres coated with tunable carbon shell for dielectric-controlled superior electromagnetic wave absorbing

To obtain high-efficiency electromagnetic wave absorbing (EMA) materials with strong reflection loss (RL) and wide effective absorption bandwidth (EAB), Ni particles are successfully prepared in this work by a liquid phase reduction method, and Ni@C is subsequently designed and fabricated through combined polymerization and carbonization process. The pristine Ni exhibits outstanding EMA performances in middle- and high-frequency with a maximum RL (RLmax) of 62.3 dB (2.3 mm) at Ku band and an EAB of 10.9 GHz (5.6-16.5 GHz) at 3.0 mm, covering 75 % Ku (12-18 GHz), 100 % X (8-12 GHz) and 60 % C (4-8 GHz) band. Such a superior performance is attributed to the dielectric loss derived from interface polarization, dipole polarization and conduction loss, along with magnetic loss comes from natural and exchange resonance. The introducing of carbon shells with manipulated thicknesses induce positive enhancement in dielectric loss. Meanwhile, core-shell structures enable multiple scattering and reflection of microwaves. Thus, Ni@C spheres exhibit significantly enhanced EMA performances in low-frequency covering S (2-4 GHz) and C band with an RLmax at 4.4 GHz reaching 64.4 dB (Ni@C-0.4) and an RLmax at 2.6 GHz reaching 59.3 dB (Ni@C-0.6). Therefore, Ni and Ni@C demonstrate a unique blend of favorable EMA performances, which is promising for the next-generation intelligent EMA systems.